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[PATCH v49 2/7] Add conditional lock feature to dshash 4+ messages / 4 participants [nested] [flat]
* [PATCH v49 2/7] Add conditional lock feature to dshash @ 2020-03-13 07:58 Kyotaro Horiguchi <[email protected]> 0 siblings, 0 replies; 4+ messages in thread From: Kyotaro Horiguchi @ 2020-03-13 07:58 UTC (permalink / raw) Dshash currently waits for lock unconditionally. It is inconvenient when we want to avoid being blocked by other processes. This commit adds alternative functions of dshash_find and dshash_find_or_insert that allows immediate return on lock failure. --- src/backend/lib/dshash.c | 98 +++++++++++++++++++++------------------- src/include/lib/dshash.h | 3 ++ 2 files changed, 55 insertions(+), 46 deletions(-) diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c index 520bfa0979..853d78b528 100644 --- a/src/backend/lib/dshash.c +++ b/src/backend/lib/dshash.c @@ -383,6 +383,10 @@ dshash_get_hash_table_handle(dshash_table *hash_table) * the caller must take care to ensure that the entry is not left corrupted. * The lock mode is either shared or exclusive depending on 'exclusive'. * + * If found is not NULL, *found is set to true if the key is found in the hash + * table. If the key is not found, *found is set to false and a pointer to a + * newly created entry is returned. + * * The caller must not lock a lock already. * * Note that the lock held is in fact an LWLock, so interrupts will be held on @@ -392,36 +396,7 @@ dshash_get_hash_table_handle(dshash_table *hash_table) void * dshash_find(dshash_table *hash_table, const void *key, bool exclusive) { - dshash_hash hash; - size_t partition; - dshash_table_item *item; - - hash = hash_key(hash_table, key); - partition = PARTITION_FOR_HASH(hash); - - Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); - - LWLockAcquire(PARTITION_LOCK(hash_table, partition), - exclusive ? LW_EXCLUSIVE : LW_SHARED); - ensure_valid_bucket_pointers(hash_table); - - /* Search the active bucket. */ - item = find_in_bucket(hash_table, key, BUCKET_FOR_HASH(hash_table, hash)); - - if (!item) - { - /* Not found. */ - LWLockRelease(PARTITION_LOCK(hash_table, partition)); - return NULL; - } - else - { - /* The caller will free the lock by calling dshash_release_lock. */ - hash_table->find_locked = true; - hash_table->find_exclusively_locked = exclusive; - return ENTRY_FROM_ITEM(item); - } + return dshash_find_extended(hash_table, key, exclusive, false, false, NULL); } /* @@ -439,31 +414,60 @@ dshash_find_or_insert(dshash_table *hash_table, const void *key, bool *found) { - dshash_hash hash; - size_t partition_index; - dshash_partition *partition; + return dshash_find_extended(hash_table, key, true, false, true, found); +} + + +/* + * Find the key in the hash table. + * + * "exclusive" is the lock mode in which the partition for the returned item + * is locked. If "nowait" is true, the function immediately returns if + * required lock was not acquired. "insert" indicates insert mode. In this + * mode new entry is inserted and set *found to false. *found is set to true if + * found. "found" must be non-null in this mode. + */ +void * +dshash_find_extended(dshash_table *hash_table, const void *key, + bool exclusive, bool nowait, bool insert, bool *found) +{ + dshash_hash hash = hash_key(hash_table, key); + size_t partidx = PARTITION_FOR_HASH(hash); + dshash_partition *partition = &hash_table->control->partitions[partidx]; + LWLockMode lockmode = exclusive ? LW_EXCLUSIVE : LW_SHARED; dshash_table_item *item; - hash = hash_key(hash_table, key); - partition_index = PARTITION_FOR_HASH(hash); - partition = &hash_table->control->partitions[partition_index]; - - Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); + /* must be exclusive when insert allowed */ + Assert(!insert || (exclusive && found != NULL)); restart: - LWLockAcquire(PARTITION_LOCK(hash_table, partition_index), - LW_EXCLUSIVE); + if (!nowait) + LWLockAcquire(PARTITION_LOCK(hash_table, partidx), lockmode); + else if (!LWLockConditionalAcquire(PARTITION_LOCK(hash_table, partidx), + lockmode)) + return NULL; + ensure_valid_bucket_pointers(hash_table); /* Search the active bucket. */ item = find_in_bucket(hash_table, key, BUCKET_FOR_HASH(hash_table, hash)); if (item) - *found = true; + { + if (found) + *found = true; + } else { - *found = false; + if (found) + *found = false; + + if (!insert) + { + /* The caller didn't told to add a new entry. */ + LWLockRelease(PARTITION_LOCK(hash_table, partidx)); + return NULL; + } /* Check if we are getting too full. */ if (partition->count > MAX_COUNT_PER_PARTITION(hash_table)) @@ -479,7 +483,8 @@ restart: * Give up our existing lock first, because resizing needs to * reacquire all the locks in the right order to avoid deadlocks. */ - LWLockRelease(PARTITION_LOCK(hash_table, partition_index)); + LWLockRelease(PARTITION_LOCK(hash_table, partidx)); + resize(hash_table, hash_table->size_log2 + 1); goto restart; @@ -493,12 +498,13 @@ restart: ++partition->count; } - /* The caller must release the lock with dshash_release_lock. */ + /* The caller will free the lock by calling dshash_release_lock. */ hash_table->find_locked = true; - hash_table->find_exclusively_locked = true; + hash_table->find_exclusively_locked = exclusive; return ENTRY_FROM_ITEM(item); } + /* * Remove an entry by key. Returns true if the key was found and the * corresponding entry was removed. diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h index a6ea377173..5b8114d041 100644 --- a/src/include/lib/dshash.h +++ b/src/include/lib/dshash.h @@ -91,6 +91,9 @@ extern void *dshash_find(dshash_table *hash_table, const void *key, bool exclusive); extern void *dshash_find_or_insert(dshash_table *hash_table, const void *key, bool *found); +extern void *dshash_find_extended(dshash_table *hash_table, const void *key, + bool exclusive, bool nowait, bool insert, + bool *found); 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); -- 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="v49-0003-Make-archiver-process-an-auxiliary-process.patch" ^ permalink raw reply [nested|flat] 4+ messages in thread
* Limit of WAL LSN value of type pg_lsn @ 2022-10-31 05:33 Shubham Shingne <[email protected]> 0 siblings, 1 reply; 4+ messages in thread From: Shubham Shingne @ 2022-10-31 05:33 UTC (permalink / raw) To: [email protected] Hi all, I am trying to determine optimal standby for automatic failover based on pg_last_wal_recieve_lsn() value of all slaves. But what if max_wal_size is reached, is LSN value reset to zero. Please share some documentation that mentions clarification. Also suggest if there is any better approach to get node with best RPO out of all slaves. Thanks & regards, Shubham ^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: Limit of WAL LSN value of type pg_lsn @ 2022-10-31 12:55 Ashutosh Bapat <[email protected]> parent: Shubham Shingne <[email protected]> 0 siblings, 0 replies; 4+ messages in thread From: Ashutosh Bapat @ 2022-10-31 12:55 UTC (permalink / raw) To: Shubham Shingne <[email protected]>; +Cc: [email protected] Hi Shubham, On Mon, Oct 31, 2022 at 11:04 AM Shubham Shingne <[email protected]> wrote: > > Hi all, > > I am trying to determine optimal standby for automatic failover based on pg_last_wal_recieve_lsn() value of all slaves. > > But what if max_wal_size is reached, is LSN value reset to zero. Per https://www.postgresql.org/docs/current/runtime-config-wal.html max_wal_size affects how frequently checkpoints are run. It doesn't specify the limit on WAL produced by a given server. Probably max_wal_size is a misnomer. LSN is never reset to zero AFAIU. > > Please share some documentation that mentions clarification. > > Also suggest if there is any better approach to get node with best RPO out of all slaves. It depends upon the method used to maintain slaves. Googling "RPO postgresql" provides a lot of links. I found http://www.postgresql-blog.com/postgresql-backup-strategy-recovery-pitr-wal/ to be a good start. But there are many others which seem to be useful too. -- Best Wishes, Ashutosh Bapat ^ permalink raw reply [nested|flat] 4+ messages in thread
* [PATCH v20 3/6] Refactor index_concurrently_create_copy() for use with REPACK (CONCURRENTLY). @ 2025-08-11 13:31 Antonin Houska <[email protected]> 0 siblings, 0 replies; 4+ messages in thread From: Antonin Houska @ 2025-08-11 13:31 UTC (permalink / raw) This patch moves the code to index_create_copy() and adds a "concurrently" parameter so it can be used by REPACK (CONCURRENTLY). With the CONCURRENTLY option, REPACK cannot simply swap the heap file and rebuild its indexes. Instead, it needs to build a separate set of indexes (including system catalog entries) *before* the actual swap, to reduce the time AccessExclusiveLock needs to be held for. --- src/backend/catalog/index.c | 36 ++++++++++++++++++++++++++++-------- src/include/catalog/index.h | 3 +++ 2 files changed, 31 insertions(+), 8 deletions(-) diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c index 3063abff9a5..0dee1b1a9d8 100644 --- a/src/backend/catalog/index.c +++ b/src/backend/catalog/index.c @@ -1290,15 +1290,31 @@ index_create(Relation heapRelation, /* * index_concurrently_create_copy * - * Create concurrently an index based on the definition of the one provided by - * caller. The index is inserted into catalogs and needs to be built later - * on. This is called during concurrent reindex processing. - * - * "tablespaceOid" is the tablespace to use for this index. + * Variant of index_create_copy(), called during concurrent reindex + * processing. */ Oid index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, Oid tablespaceOid, const char *newName) +{ + return index_create_copy(heapRelation, oldIndexId, tablespaceOid, newName, + true); +} + +/* + * index_create_copy + * + * Create an index based on the definition of the one provided by caller. The + * index is inserted into catalogs and needs to be built later on. + * + * "tablespaceOid" is the tablespace to use for this index. + * + * The actual implementation of index_concurrently_create_copy(), reusable for + * other purposes. + */ +Oid +index_create_copy(Relation heapRelation, Oid oldIndexId, Oid tablespaceOid, + const char *newName, bool concurrently) { Relation indexRelation; IndexInfo *oldInfo, @@ -1317,6 +1333,7 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, List *indexColNames = NIL; List *indexExprs = NIL; List *indexPreds = NIL; + int flags = 0; indexRelation = index_open(oldIndexId, RowExclusiveLock); @@ -1325,9 +1342,9 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, /* * Concurrent build of an index with exclusion constraints is not - * supported. + * supported. If !concurrently, ii_ExclusinOps is currently not needed. */ - if (oldInfo->ii_ExclusionOps != NULL) + if (oldInfo->ii_ExclusionOps != NULL && concurrently) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("concurrent index creation for exclusion constraints is not supported"))); @@ -1435,6 +1452,9 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, stattargets[i].isnull = isnull; } + if (concurrently) + flags = INDEX_CREATE_SKIP_BUILD | INDEX_CREATE_CONCURRENT; + /* * Now create the new index. * @@ -1458,7 +1478,7 @@ index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, indcoloptions->values, stattargets, reloptionsDatum, - INDEX_CREATE_SKIP_BUILD | INDEX_CREATE_CONCURRENT, + flags, 0, true, /* allow table to be a system catalog? */ false, /* is_internal? */ diff --git a/src/include/catalog/index.h b/src/include/catalog/index.h index 4daa8bef5ee..063a891351a 100644 --- a/src/include/catalog/index.h +++ b/src/include/catalog/index.h @@ -99,6 +99,9 @@ extern Oid index_concurrently_create_copy(Relation heapRelation, Oid oldIndexId, Oid tablespaceOid, const char *newName); +extern Oid index_create_copy(Relation heapRelation, Oid oldIndexId, + Oid tablespaceOid, const char *newName, + bool concurrently); extern void index_concurrently_build(Oid heapRelationId, Oid indexRelationId); -- 2.39.5 --3q6txozlgl6t37td Content-Type: text/x-diff; charset=utf-8 Content-Disposition: attachment; filename="v20-0004-Move-conversion-of-a-historic-to-MVCC-snapshot-t.patch" ^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2025-08-11 13:31 UTC | newest] Thread overview: 4+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2020-03-13 07:58 [PATCH v49 2/7] Add conditional lock feature to dshash Kyotaro Horiguchi <[email protected]> 2022-10-31 05:33 Limit of WAL LSN value of type pg_lsn Shubham Shingne <[email protected]> 2022-10-31 12:55 ` Re: Limit of WAL LSN value of type pg_lsn Ashutosh Bapat <[email protected]> 2025-08-11 13:31 [PATCH v20 3/6] Refactor index_concurrently_create_copy() for use with REPACK (CONCURRENTLY). Antonin Houska <[email protected]>
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