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[PATCH v24 1/5] sequential scan for dshash
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* [PATCH v24 1/5] sequential scan for dshash
@ 2018-06-29 07:41 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2018-06-29 07:41 UTC (permalink / raw)

Add sequential scan feature to dshash.
---
 src/backend/lib/dshash.c | 188 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  23 ++++-
 2 files changed, 206 insertions(+), 5 deletions(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 350f8c0a66..4f0c7ec840 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -112,6 +112,7 @@ struct dshash_table
 	size_t		size_log2;		/* log2(number of buckets) */
 	bool		find_locked;	/* Is any partition lock held by 'find'? */
 	bool		find_exclusively_locked;	/* ... exclusively? */
+	bool		seqscan_running;/* now under sequential scan */
 };
 
 /* Given a pointer to an item, find the entry (user data) it holds. */
@@ -127,6 +128,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +158,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -228,6 +237,7 @@ dshash_create(dsa_area *area, const dshash_parameters *params, void *arg)
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 
 	/*
 	 * Set up the initial array of buckets.  Our initial size is the same as
@@ -279,6 +289,7 @@ dshash_attach(dsa_area *area, const dshash_parameters *params,
 	hash_table->control = dsa_get_address(area, control);
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 	Assert(hash_table->control->magic == DSHASH_MAGIC);
 
 	/*
@@ -324,7 +335,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -549,9 +560,14 @@ dshash_delete_entry(dshash_table *hash_table, void *entry)
 								LW_EXCLUSIVE));
 
 	delete_item(hash_table, item);
-	hash_table->find_locked = false;
-	hash_table->find_exclusively_locked = false;
-	LWLockRelease(PARTITION_LOCK(hash_table, partition));
+
+	/* We need to keep partition lock while sequential scan */
+	if (!hash_table->seqscan_running)
+	{
+		hash_table->find_locked = false;
+		hash_table->find_exclusively_locked = false;
+		LWLockRelease(PARTITION_LOCK(hash_table, partition));
+	}
 }
 
 /*
@@ -568,6 +584,8 @@ dshash_release_lock(dshash_table *hash_table, void *entry)
 	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition_index),
 								hash_table->find_exclusively_locked
 								? LW_EXCLUSIVE : LW_SHARED));
+	/* lock is under control of sequential scan */
+	Assert(!hash_table->seqscan_running);
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
@@ -592,6 +610,168 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan trhough dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should be called if and only if the scan is abandoned
+ * before completion; if dshash_seq_next returns NULL then it has already done
+ * the end-of-scan cleanup.
+ *
+ * On returning element, it is locked as is the case with dshash_find.
+ * However, the caller must not release the lock. The lock is released as
+ * necessary in continued scan.
+ *
+ * As opposed to the equivalent for dynanash, the caller is not supposed to
+ * delete the returned element before continuing the scan.
+ *
+ * If consistent is set for dshash_seq_init, the whole hash table is
+ * non-exclusively locked. Otherwise a part of the hash table is locked in the
+ * same mode (partition lock).
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool consistent, bool exclusive)
+{
+	/* allowed at most one scan at once */
+	Assert(!hash_table->seqscan_running);
+
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->consistent = consistent;
+	status->exclusive = exclusive;
+	hash_table->seqscan_running = true;
+
+	/*
+	 * Protect all partitions from modification if the caller wants a
+	 * consistent result.
+	 */
+	if (consistent)
+	{
+		int i;
+
+		for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+		{
+			Assert(!LWLockHeldByMe(PARTITION_LOCK(hash_table, i)));
+
+			LWLockAcquire(PARTITION_LOCK(hash_table, i),
+						  exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		}
+		ensure_valid_bucket_pointers(hash_table);
+	}
+}
+
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	Assert(status->hash_table->seqscan_running);
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert (status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		if (!status->consistent)
+		{
+			partition =
+				PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+										   status->hash_table->size_log2);
+			LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			status->curpartition = partition;
+
+			/* resize doesn't happen from now until seq scan ends */
+			status->nbuckets =
+				NUM_BUCKETS(status->hash_table->control->size_log2);
+			ensure_valid_bucket_pointers(status->hash_table);
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finsih. */
+			dshash_seq_term(status);
+			return NULL;
+		}
+
+		/* Also move parititon lock if needed */
+		if (!status->consistent)
+		{
+			int next_partition =
+				PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+										   status->hash_table->size_log2);
+
+			/* Move lock along with partition for the bucket */
+			if (status->curpartition != next_partition)
+			{
+				/*
+				 * Take lock on the next partition then release the current,
+				 * not in the reverse order. This is required to avoid
+				 * resizing from happening during a sequential scan. Locks are
+				 * taken in partition order so no dead lock happen with other
+				 * seq scans or resizing.
+				 */
+				LWLockAcquire(PARTITION_LOCK(status->hash_table,
+											 next_partition),
+							  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+				LWLockRelease(PARTITION_LOCK(status->hash_table,
+											 status->curpartition));
+				status->curpartition = next_partition;
+			}
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * This item can be deleted by the caller. Store the next item for the
+	 * next iteration for the occasion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	Assert(status->hash_table->seqscan_running);
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+	status->hash_table->seqscan_running = false;
+
+	if (status->consistent)
+	{
+		int i;
+
+		for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+			LWLockRelease(PARTITION_LOCK(status->hash_table, i));
+	}
+	else if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index fa2e28ff3e..79698a6ad6 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,23 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state of dshash. The detail is exposed since the storage
+ * size should be known to users but it should be considered as an opaque
+ * type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;
+	int					curbucket;
+	int					nbuckets;
+	dshash_table_item  *curitem;
+	dsa_pointer			pnextitem;
+	int					curpartition;
+	bool				consistent;
+	bool				exclusive;
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -70,7 +87,6 @@ extern dshash_table *dshash_attach(dsa_area *area,
 extern void dshash_detach(dshash_table *hash_table);
 extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table);
 extern void dshash_destroy(dshash_table *hash_table);
-
 /* Finding, creating, deleting entries. */
 extern void *dshash_find(dshash_table *hash_table,
 						 const void *key, bool exclusive);
@@ -80,6 +96,11 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool consistent, bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.23.0


----Next_Part(Tue_Dec__3_17_27_59_2019_887)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v24-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH 1/5] sequential scan for dshash
@ 2018-06-29 07:41 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2018-06-29 07:41 UTC (permalink / raw)

Add sequential scan feature to dshash.
---
 src/backend/lib/dshash.c | 185 +++++++++++++++++++++++++++++++++++++--
 src/include/lib/dshash.h |  22 ++++-
 2 files changed, 201 insertions(+), 6 deletions(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index fbdd941325..7675370058 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -112,6 +112,7 @@ struct dshash_table
 	size_t		size_log2;		/* log2(number of buckets) */
 	bool		find_locked;	/* Is any partition lock held by 'find'? */
 	bool		find_exclusively_locked;	/* ... exclusively? */
+	bool		seqscan_running;/* now under sequential scan */
 };
 
 /* Given a pointer to an item, find the entry (user data) it holds. */
@@ -127,6 +128,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +158,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -228,6 +237,7 @@ dshash_create(dsa_area *area, const dshash_parameters *params, void *arg)
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 
 	/*
 	 * Set up the initial array of buckets.  Our initial size is the same as
@@ -279,6 +289,7 @@ dshash_attach(dsa_area *area, const dshash_parameters *params,
 	hash_table->control = dsa_get_address(area, control);
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 	Assert(hash_table->control->magic == DSHASH_MAGIC);
 
 	/*
@@ -324,7 +335,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -549,9 +560,14 @@ dshash_delete_entry(dshash_table *hash_table, void *entry)
 								LW_EXCLUSIVE));
 
 	delete_item(hash_table, item);
-	hash_table->find_locked = false;
-	hash_table->find_exclusively_locked = false;
-	LWLockRelease(PARTITION_LOCK(hash_table, partition));
+
+	/* We need to keep partition lock while sequential scan */
+	if (!hash_table->seqscan_running)
+	{
+		hash_table->find_locked = false;
+		hash_table->find_exclusively_locked = false;
+		LWLockRelease(PARTITION_LOCK(hash_table, partition));
+	}
 }
 
 /*
@@ -568,6 +584,8 @@ dshash_release_lock(dshash_table *hash_table, void *entry)
 	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition_index),
 								hash_table->find_exclusively_locked
 								? LW_EXCLUSIVE : LW_SHARED));
+	/* lock is under control of sequential scan */
+	Assert(!hash_table->seqscan_running);
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
@@ -592,6 +610,164 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan trhough dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should be called for incomplete scans and otherwise
+ * shoudln't. Finished scans are cleaned up automatically.
+ *
+ * Returned elements are locked as is the case with dshash_find.  However, the
+ * caller must not release the lock.
+ *
+ * Same as dynanash, the caller may delete returned elements midst of a scan.
+ *
+ * If consistent is set for dshash_seq_init, the all hash table partitions are
+ * locked in the requested mode (as determined by the exclusive flag) during
+ * the scan.  Otherwise partitions are locked in one-at-a-time way during the
+ * scan.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool consistent, bool exclusive)
+{
+	/* allowed at most one scan at once */
+	Assert(!hash_table->seqscan_running);
+
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->consistent = consistent;
+	status->exclusive = exclusive;
+	hash_table->seqscan_running = true;
+
+	/*
+	 * Protect all partitions from modification if the caller wants a
+	 * consistent result.
+	 */
+	if (consistent)
+	{
+		int i;
+
+		for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+		{
+			Assert(!LWLockHeldByMe(PARTITION_LOCK(hash_table, i)));
+
+			LWLockAcquire(PARTITION_LOCK(hash_table, i),
+						  exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		}
+		ensure_valid_bucket_pointers(hash_table);
+	}
+}
+
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	Assert(status->hash_table->seqscan_running);
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert (status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		if (!status->consistent)
+		{
+			partition =
+				PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+										   status->hash_table->size_log2);
+			LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			status->curpartition = partition;
+
+			/* resize doesn't happen from now until seq scan ends */
+			status->nbuckets =
+				NUM_BUCKETS(status->hash_table->control->size_log2);
+			ensure_valid_bucket_pointers(status->hash_table);
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finsih. */
+			dshash_seq_term(status);
+			return NULL;
+		}
+
+		/* Also move parititon lock if needed */
+		if (!status->consistent)
+		{
+			int next_partition =
+				PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+										   status->hash_table->size_log2);
+
+			/* Move lock along with partition for the bucket */
+			if (status->curpartition != next_partition)
+			{
+				/*
+				 * Lock the next partition then release the current, not in the
+				 * reverse order to to avoid concurrent resizing. Partitions
+				 * are locked in the same order with resize() so dead locks
+				 * won't happen.
+				 */
+				LWLockAcquire(PARTITION_LOCK(status->hash_table,
+											 next_partition),
+							  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+				LWLockRelease(PARTITION_LOCK(status->hash_table,
+											 status->curpartition));
+				status->curpartition = next_partition;
+			}
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	Assert(status->hash_table->seqscan_running);
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+	status->hash_table->seqscan_running = false;
+
+	if (status->consistent)
+	{
+		int i;
+
+		for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i)
+			LWLockRelease(PARTITION_LOCK(status->hash_table, i));
+	}
+	else if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
@@ -673,7 +849,6 @@ delete_item(dshash_table *hash_table, dshash_table_item *item)
 /*
  * Grow the hash table if necessary to the requested number of buckets.  The
  * requested size must be double some previously observed size.
- *
  * Must be called without any partition lock held.
  */
 static void
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..ad88f32cdd 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,22 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;
+	int					curbucket;
+	int					nbuckets;
+	dshash_table_item  *curitem;
+	dsa_pointer			pnextitem;
+	int					curpartition;
+	bool				consistent;
+	bool				exclusive;
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -70,7 +86,6 @@ extern dshash_table *dshash_attach(dsa_area *area,
 extern void dshash_detach(dshash_table *hash_table);
 extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table);
 extern void dshash_destroy(dshash_table *hash_table);
-
 /* Finding, creating, deleting entries. */
 extern void *dshash_find(dshash_table *hash_table,
 						 const void *key, bool exclusive);
@@ -80,6 +95,11 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool consistent, bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.23.0


----Next_Part(Wed_Jan_22_17_24_04_2020_620)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v49 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_16_53_11_2021_575)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v49-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v46 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_14_15_14_25_2021_903)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v46-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v51 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_12_10_39_2021_432)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v51-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v45 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Fri_Jan__8_10_24_34_2021_185)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v45-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v38 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 78ccf03217..b829167872 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..c337099061 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.18.4


----Next_Part(Thu_Oct__1_09_07_22_2020_252)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v38-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v51 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_12_10_39_2021_432)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v51-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v49 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_16_53_11_2021_575)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v49-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v50 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_18_29_34_2021_806)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v50-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v49 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_16_53_11_2021_575)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v49-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v52 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e4d2debb3c..21fd98af66 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_17_51_37_2021_192)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v52-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v31 2/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 149 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  21 ++++++
 2 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 78ccf03217..1ef093e2e9 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,145 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..0ca9514021 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,12 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.18.2


----Next_Part(Fri_Apr__3_17_31_17_2020_104)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v31-0003-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v25 2/8] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 162 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  21 +++++
 2 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 78ccf03217..2086bdbea9 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -112,6 +112,7 @@ struct dshash_table
 	size_t		size_log2;		/* log2(number of buckets) */
 	bool		find_locked;	/* Is any partition lock held by 'find'? */
 	bool		find_exclusively_locked;	/* ... exclusively? */
+	bool		seqscan_running;/* now under sequential scan */
 };
 
 /* Given a pointer to an item, find the entry (user data) it holds. */
@@ -127,6 +128,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +158,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -228,6 +237,7 @@ dshash_create(dsa_area *area, const dshash_parameters *params, void *arg)
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 
 	/*
 	 * Set up the initial array of buckets.  Our initial size is the same as
@@ -279,6 +289,7 @@ dshash_attach(dsa_area *area, const dshash_parameters *params,
 	hash_table->control = dsa_get_address(area, control);
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
+	hash_table->seqscan_running = false;
 	Assert(hash_table->control->magic == DSHASH_MAGIC);
 
 	/*
@@ -324,7 +335,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -568,6 +579,8 @@ dshash_release_lock(dshash_table *hash_table, void *entry)
 	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition_index),
 								hash_table->find_exclusively_locked
 								? LW_EXCLUSIVE : LW_SHARED));
+	/* lock is under control of sequential scan */
+	Assert(!hash_table->seqscan_running);
 
 	hash_table->find_locked = false;
 	hash_table->find_exclusively_locked = false;
@@ -592,6 +605,153 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	/* allowed at most one scan at once */
+	Assert(!hash_table->seqscan_running);
+
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+	hash_table->seqscan_running = true;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	Assert(status->hash_table->seqscan_running);
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert (status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Also move parititon lock if needed */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		/* Move lock along with partition for the bucket */
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Lock the next partition then release the current, not in the
+			 * reverse order to avoid concurrent resizing. Partitions are
+			 * locked in the same order with resize() so dead locks won't
+			 * happen.
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	Assert(status->hash_table->seqscan_running);
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+	status->hash_table->seqscan_running = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..81a929b8d9 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;
+	int					curbucket;
+	int					nbuckets;
+	dshash_table_item  *curitem;
+	dsa_pointer			pnextitem;
+	int					curpartition;
+	bool				exclusive;
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,12 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.18.2


----Next_Part(Thu_Mar_19_20_30_04_2020_284)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v25-0003-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v51 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_12_10_39_2021_432)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v51-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v47 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_21_12_03_48_2021_284)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v47-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v46 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_14_15_14_25_2021_903)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v46-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v41 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 78ccf03217..b829167872 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..c337099061 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.18.4


----Next_Part(Fri_Nov__6_09_27_56_2020_738)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v41-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v52 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e4d2debb3c..21fd98af66 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_17_51_37_2021_192)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v52-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v45 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Fri_Jan__8_10_24_34_2021_185)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v45-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v47 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_21_12_03_48_2021_284)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v47-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v37 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 149 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  21 ++++++
 2 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 78ccf03217..1ef093e2e9 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,145 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index b86df68e77..0ca9514021 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,12 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.18.4


----Next_Part(Fri_Sep_25_09_27_26_2020_419)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v37-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v46 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_14_15_14_25_2021_903)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v46-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v50 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_18_29_34_2021_806)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v50-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v47 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Thu_Jan_21_12_03_48_2021_284)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v47-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v45 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c | 160 ++++++++++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h |  22 ++++++
 2 files changed, 181 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
-- 
2.27.0


----Next_Part(Fri_Jan__8_10_24_34_2021_185)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v45-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v52 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e4d2debb3c..21fd98af66 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_17_51_37_2021_192)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v52-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v52 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e4d2debb3c..21fd98af66 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_17_51_37_2021_192)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v52-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v52 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index e4d2debb3c..21fd98af66 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Wed_Mar_10_17_51_37_2021_192)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v52-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v56 1/6] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This commit
adds the functionality.  The interface is similar but a bit different
both from that of dynahash and simple dshash search functions.  One of
the most significant differences is the sequential scan interface of
dshash always needs a call to dshash_seq_term when scan ends. Another
is locking.  Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a scan.
The seqscan interface allows entry deletion while a scan is in
progress. The in-scan deletion should be performed by
dshash_delete_current().
---
 src/backend/lib/dshash.c         | 161 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 183 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..29ad767618 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,157 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition PG_USED_FOR_ASSERTS_ONLY
+		= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 61cf4eae1f..78e852569e 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2958,6 +2958,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar_16_10_27_55_2021_500)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v56-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v50 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


----Next_Part(Tue_Mar__9_18_29_34_2021_806)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v50-0002-Add-conditional-lock-feature-to-dshash.patch"



^ permalink  raw  reply  [nested|flat] 230+ messages in thread

* [PATCH v50 1/7] sequential scan for dshash
@ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]>
  0 siblings, 0 replies; 230+ messages in thread

From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw)

Dshash did not allow scan the all entries sequentially. This adds the
functionality. The interface is similar but a bit different both from
that of dynahash and simple dshash search functions. One of the most
significant differences is the sequential scan interface of dshash
always needs a call to dshash_seq_term when scan ends. Another is
locking. Dshash holds partition lock when returning an entry,
dshash_seq_next() also holds lock when returning an entry but callers
shouldn't release it, since the lock is essential to continue a
scan. The seqscan interface allows entry deletion while a scan. The
in-scan deletion should be performed by dshash_delete_current().
---
 src/backend/lib/dshash.c         | 160 ++++++++++++++++++++++++++++++-
 src/include/lib/dshash.h         |  22 +++++
 src/tools/pgindent/typedefs.list |   1 +
 3 files changed, 182 insertions(+), 1 deletion(-)

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index e0c763be32..520bfa0979 100644
--- a/src/backend/lib/dshash.c
+++ b/src/backend/lib/dshash.c
@@ -127,6 +127,10 @@ struct dshash_table
 #define NUM_SPLITS(size_log2)					\
 	(size_log2 - DSHASH_NUM_PARTITIONS_LOG2)
 
+/* How many buckets are there in a given size? */
+#define NUM_BUCKETS(size_log2)		\
+	(((size_t) 1) << (size_log2))
+
 /* How many buckets are there in each partition at a given size? */
 #define BUCKETS_PER_PARTITION(size_log2)		\
 	(((size_t) 1) << NUM_SPLITS(size_log2))
@@ -153,6 +157,10 @@ struct dshash_table
 #define BUCKET_INDEX_FOR_PARTITION(partition, size_log2)	\
 	((partition) << NUM_SPLITS(size_log2))
 
+/* Choose partition based on bucket index. */
+#define PARTITION_FOR_BUCKET_INDEX(bucket_idx, size_log2)				\
+	((bucket_idx) >> NUM_SPLITS(size_log2))
+
 /* The head of the active bucket for a given hash value (lvalue). */
 #define BUCKET_FOR_HASH(hash_table, hash)								\
 	(hash_table->buckets[												\
@@ -324,7 +332,7 @@ dshash_destroy(dshash_table *hash_table)
 	ensure_valid_bucket_pointers(hash_table);
 
 	/* Free all the entries. */
-	size = ((size_t) 1) << hash_table->size_log2;
+	size = NUM_BUCKETS(hash_table->size_log2);
 	for (i = 0; i < size; ++i)
 	{
 		dsa_pointer item_pointer = hash_table->buckets[i];
@@ -592,6 +600,156 @@ dshash_memhash(const void *v, size_t size, void *arg)
 	return tag_hash(v, size);
 }
 
+/*
+ * dshash_seq_init/_next/_term
+ *           Sequentially scan through dshash table and return all the
+ *           elements one by one, return NULL when no more.
+ *
+ * dshash_seq_term should always be called when a scan finished.
+ * The caller may delete returned elements midst of a scan by using
+ * dshash_delete_current(). exclusive must be true to delete elements.
+ */
+void
+dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+				bool exclusive)
+{
+	status->hash_table = hash_table;
+	status->curbucket = 0;
+	status->nbuckets = 0;
+	status->curitem = NULL;
+	status->pnextitem = InvalidDsaPointer;
+	status->curpartition = -1;
+	status->exclusive = exclusive;
+}
+
+/*
+ * Returns the next element.
+ *
+ * Returned elements are locked and the caller must not explicitly release
+ * it. It is released at the next call to dshash_next().
+ */
+void *
+dshash_seq_next(dshash_seq_status *status)
+{
+	dsa_pointer next_item_pointer;
+
+	if (status->curitem == NULL)
+	{
+		int partition;
+
+		Assert(status->curbucket == 0);
+		Assert(!status->hash_table->find_locked);
+
+		/* first shot. grab the first item. */
+		partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+		LWLockAcquire(PARTITION_LOCK(status->hash_table, partition),
+					  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+		status->curpartition = partition;
+
+		/* resize doesn't happen from now until seq scan ends */
+		status->nbuckets =
+			NUM_BUCKETS(status->hash_table->control->size_log2);
+		ensure_valid_bucket_pointers(status->hash_table);
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+	else
+		next_item_pointer = status->pnextitem;
+
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(status->hash_table,
+											   status->curpartition),
+								status->exclusive ? LW_EXCLUSIVE : LW_SHARED));
+
+	/* Move to the next bucket if we finished the current bucket */
+	while (!DsaPointerIsValid(next_item_pointer))
+	{
+		int next_partition;
+
+		if (++status->curbucket >= status->nbuckets)
+		{
+			/* all buckets have been scanned. finish. */
+			return NULL;
+		}
+
+		/* Check if move to the next partition */
+		next_partition =
+			PARTITION_FOR_BUCKET_INDEX(status->curbucket,
+									   status->hash_table->size_log2);
+
+		if (status->curpartition != next_partition)
+		{
+			/*
+			 * Move to the next partition. Lock the next partition then release
+			 * the current, not in the reverse order to avoid concurrent
+			 * resizing.  Avoid dead lock by taking lock in the same order
+			 * with resize().
+			 */
+			LWLockAcquire(PARTITION_LOCK(status->hash_table,
+										 next_partition),
+						  status->exclusive ? LW_EXCLUSIVE : LW_SHARED);
+			LWLockRelease(PARTITION_LOCK(status->hash_table,
+										 status->curpartition));
+			status->curpartition = next_partition;
+		}
+
+		next_item_pointer = status->hash_table->buckets[status->curbucket];
+	}
+
+	status->curitem =
+		dsa_get_address(status->hash_table->area, next_item_pointer);
+	status->hash_table->find_locked = true;
+	status->hash_table->find_exclusively_locked = status->exclusive;
+
+	/*
+	 * The caller may delete the item. Store the next item in case of deletion.
+	 */
+	status->pnextitem = status->curitem->next;
+
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
+/*
+ * Terminates the seqscan and release all locks.
+ *
+ * Should be always called when finishing or exiting a seqscan.
+ */
+void
+dshash_seq_term(dshash_seq_status *status)
+{
+	status->hash_table->find_locked = false;
+	status->hash_table->find_exclusively_locked = false;
+
+	if (status->curpartition >= 0)
+		LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
+}
+
+/* Remove the current entry while a seq scan. */
+void
+dshash_delete_current(dshash_seq_status *status)
+{
+	dshash_table	   *hash_table	= status->hash_table;
+	dshash_table_item  *item		= status->curitem;
+	size_t				partition	= PARTITION_FOR_HASH(item->hash);
+
+	Assert(status->exclusive);
+	Assert(hash_table->control->magic == DSHASH_MAGIC);
+	Assert(hash_table->find_locked);
+	Assert(hash_table->find_exclusively_locked);
+	Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition),
+								LW_EXCLUSIVE));
+
+	delete_item(hash_table, item);
+}
+
+/* Get the current entry while a seq scan. */
+void *
+dshash_get_current(dshash_seq_status *status)
+{
+	return ENTRY_FROM_ITEM(status->curitem);
+}
+
 /*
  * Print debugging information about the internal state of the hash table to
  * stderr.  The caller must hold no partition locks.
diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index c069ec9de7..a6ea377173 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -59,6 +59,21 @@ typedef struct dshash_parameters
 struct dshash_table_item;
 typedef struct dshash_table_item dshash_table_item;
 
+/*
+ * Sequential scan state. The detail is exposed to let users know the storage
+ * size but it should be considered as an opaque type by callers.
+ */
+typedef struct dshash_seq_status
+{
+	dshash_table	   *hash_table;	/* dshash table working on */
+	int					curbucket;	/* bucket number we are at */
+	int					nbuckets;	/* total number of buckets in the dshash */
+	dshash_table_item  *curitem;	/* item we are currently at */
+	dsa_pointer			pnextitem;	/* dsa-pointer to the next item */
+	int					curpartition;	/* partition number we are at */
+	bool				exclusive;	/* locking mode */
+} dshash_seq_status;
+
 /* Creating, sharing and destroying from hash tables. */
 extern dshash_table *dshash_create(dsa_area *area,
 								   const dshash_parameters *params,
@@ -80,6 +95,13 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* seq scan support */
+extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
+							bool exclusive);
+extern void *dshash_seq_next(dshash_seq_status *status);
+extern void dshash_seq_term(dshash_seq_status *status);
+extern void dshash_delete_current(dshash_seq_status *status);
+extern void *dshash_get_current(dshash_seq_status *status);
 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */
 extern int	dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8bd95aefa1..2b591e94e6 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2954,6 +2954,7 @@ dshash_hash
 dshash_hash_function
 dshash_parameters
 dshash_partition
+dshash_seq_status
 dshash_table
 dshash_table_control
 dshash_table_handle
-- 
2.27.0


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Content-Transfer-Encoding: 7bit
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 filename="v50-0002-Add-conditional-lock-feature-to-dshash.patch"



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