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Subject: [PATCH v1 06/14] heapam: Add batch mode mvcc check and use it in page mode
Date: Thu, 17 Oct 2024 13:16:36 -0400
There are two reasons for doing so:
1) It is generally faster to perform checks in a batched fashion and making
sequential scans faster is nice.
2) We would like to stop setting hint bits while pages are being written
out. The necessary locking becomes visible for page mode scans if done for
every tuple. With batching the overhead can be amortized to only happen
once per page.
There are substantial further optimization opportunities along these
lines:
- Right now HeapTupleSatisfiesMVCCBatch() simply uses the single-tuple
HeapTupleSatisfiesMVCC(), relying on the compiler to inline it. We could
instead write an explicitly optimized version that avoids repeated xid
tests.
- Introduce batched version of the serializability test
- Introduce batched version of HeapTupleSatisfiesVacuum
Author:
Reviewed-by:
Discussion: https://postgr.es/m/
Backpatch:
---
src/include/access/heapam.h | 28 +++++
src/backend/access/heap/heapam.c | 110 ++++++++++++++++----
src/backend/access/heap/heapam_visibility.c | 50 +++++++++
src/tools/pgindent/typedefs.list | 1 +
4 files changed, 166 insertions(+), 23 deletions(-)
diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 96cf82f97b7..d4a790251cc 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -417,6 +417,34 @@ extern bool HeapTupleHeaderIsOnlyLocked(HeapTupleHeader tuple);
extern bool HeapTupleIsSurelyDead(HeapTuple htup,
struct GlobalVisState *vistest);
+/*
+ * FIXME: define to be removed
+ *
+ * Without this I see worse performance. But it's a bit ugly, so I thought
+ * it'd be useful to leave a way in for others to experiment with this.
+ */
+#define BATCHMVCC_FEWER_ARGS
+
+#ifdef BATCHMVCC_FEWER_ARGS
+typedef struct BatchMVCCState
+{
+ HeapTupleData tuples[MaxHeapTuplesPerPage];
+ bool visible[MaxHeapTuplesPerPage];
+} BatchMVCCState;
+#endif
+
+extern int HeapTupleSatisfiesMVCCBatch(Snapshot snapshot, Buffer buffer,
+ int ntups,
+#ifdef BATCHMVCC_FEWER_ARGS
+ BatchMVCCState *batchmvcc,
+#else
+ HeapTupleData *tuples,
+ bool *visible,
+#endif
+ OffsetNumber *vistuples_dense);
+
+
+
/*
* To avoid leaking too much knowledge about reorderbuffer implementation
* details this is implemented in reorderbuffer.c not heapam_visibility.c
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index d0cb4b1e29b..99656a1aac5 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -437,42 +437,106 @@ page_collect_tuples(HeapScanDesc scan, Snapshot snapshot,
BlockNumber block, int lines,
bool all_visible, bool check_serializable)
{
+ Oid relid = RelationGetRelid(scan->rs_base.rs_rd);
+#ifdef BATCHMVCC_FEWER_ARGS
+ BatchMVCCState batchmvcc;
+#else
+ HeapTupleData tuples[MaxHeapTuplesPerPage];
+ bool visible[MaxHeapTuplesPerPage];
+#endif
int ntup = 0;
- OffsetNumber lineoff;
+ int nvis = 0;
- for (lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++)
+ /* page at a time should have been disabled otherwise */
+ Assert(IsMVCCSnapshot(snapshot));
+
+ /* first find all tuples on the page */
+ for (OffsetNumber lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++)
{
ItemId lpp = PageGetItemId(page, lineoff);
- HeapTupleData loctup;
- bool valid;
+ HeapTuple tup;
- if (!ItemIdIsNormal(lpp))
+ if (unlikely(!ItemIdIsNormal(lpp)))
continue;
- loctup.t_data = (HeapTupleHeader) PageGetItem(page, lpp);
- loctup.t_len = ItemIdGetLength(lpp);
- loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd);
- ItemPointerSet(&(loctup.t_self), block, lineoff);
-
- if (all_visible)
- valid = true;
- else
- valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
-
- if (check_serializable)
- HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd,
- &loctup, buffer, snapshot);
-
- if (valid)
+ /*
+ * If the page is not all-visible or we need to check serializability,
+ * maintain enough state to be able to refind the tuple efficiently,
+ * without again needing to extract it from the page.
+ */
+ if (!all_visible || check_serializable)
{
- scan->rs_vistuples[ntup] = lineoff;
- ntup++;
+#ifdef BATCHMVCC_FEWER_ARGS
+ tup = &batchmvcc.tuples[ntup];
+#else
+ tup = &tuples[ntup];
+#endif
+
+ tup->t_data = (HeapTupleHeader) PageGetItem(page, lpp);
+ tup->t_len = ItemIdGetLength(lpp);
+ tup->t_tableOid = relid;
+ ItemPointerSet(&(tup->t_self), block, lineoff);
}
+
+ /*
+ * If the page is all visible, these fields won'otherwise wont be
+ * populated in loop below.
+ */
+ if (all_visible)
+ {
+ if (check_serializable)
+ {
+#ifdef BATCHMVCC_FEWER_ARGS
+ batchmvcc.visible[ntup] = true;
+#else
+ visible[ntup] = true;
+#endif
+ }
+ scan->rs_vistuples[ntup] = lineoff;
+ }
+
+ ntup++;
}
Assert(ntup <= MaxHeapTuplesPerPage);
- return ntup;
+ /* unless the page is all visible, test visibility for all tuples one go */
+ if (all_visible)
+ nvis = ntup;
+ else
+ nvis = HeapTupleSatisfiesMVCCBatch(snapshot, buffer,
+ ntup,
+#ifdef BATCHMVCC_FEWER_ARGS
+ &batchmvcc,
+#else
+ tuples, visible,
+#endif
+ scan->rs_vistuples
+ );
+
+ /*
+ * So far we don't have batch API for testing serializabilty, so do so
+ * one-by-one.
+ */
+ if (check_serializable)
+ {
+ for (int i = 0; i < ntup; i++)
+ {
+#ifdef BATCHMVCC_FEWER_ARGS
+ HeapCheckForSerializableConflictOut(batchmvcc.visible[i],
+ scan->rs_base.rs_rd,
+ &batchmvcc.tuples[i],
+ buffer, snapshot);
+#else
+ HeapCheckForSerializableConflictOut(visible[i],
+ scan->rs_base.rs_rd,
+ &tuples[i],
+ buffer, snapshot);
+#endif
+ }
+ }
+
+ return nvis;
}
/*
diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c
index b7aa8bb7a52..4baafc01a2c 100644
--- a/src/backend/access/heap/heapam_visibility.c
+++ b/src/backend/access/heap/heapam_visibility.c
@@ -1575,6 +1575,56 @@ HeapTupleSatisfiesHistoricMVCC(HeapTuple htup, Snapshot snapshot,
return true;
}
+/*
+ * Perform HeaptupleSatisfiesMVCC() on each passed in tuple. This is more
+ * efficient than doing HeapTupleSatisfiesMVCC() one-by-one.
+ *
+ * To be checked tuples are passed via BatchMVCCState->tuples. Each tuple's
+ * visibility is set in batchmvcc->visible[]. In addition, ->vistuples_dense
+ * is set to contain the offsets of visible tuples.
+ *
+ * Returns the number of visible tuples.
+ */
+int
+HeapTupleSatisfiesMVCCBatch(Snapshot snapshot, Buffer buffer,
+ int ntups,
+#ifdef BATCHMVCC_FEWER_ARGS
+ BatchMVCCState *batchmvcc,
+#else
+ HeapTupleData *tuples,
+ bool *visible,
+#endif
+ OffsetNumber *vistuples_dense)
+{
+ int nvis = 0;
+
+ Assert(IsMVCCSnapshot(snapshot));
+
+ for (int i = 0; i < ntups; i++)
+ {
+ bool valid;
+#ifdef BATCHMVCC_FEWER_ARGS
+ HeapTuple tup = &batchmvcc->tuples[i];
+#else
+ HeapTuple tup = &tuples[i];
+#endif
+
+ valid = HeapTupleSatisfiesMVCC(tup, snapshot, buffer);
+#ifdef BATCHMVCC_FEWER_ARGS
+ batchmvcc->visible[i] = valid;
+#else
+ visible[i] = valid;
+#endif
+ if (likely(valid))
+ {
+ vistuples_dense[nvis] = tup->t_self.ip_posid;
+ nvis++;
+ }
+ }
+
+ return nvis;
+}
+
/*
* HeapTupleSatisfiesVisibility
* True iff heap tuple satisfies a time qual.
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 171a7dd5d2b..15c7673465b 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -244,6 +244,7 @@ Barrier
BaseBackupCmd
BaseBackupTargetHandle
BaseBackupTargetType
+BatchMVCCState
BeginDirectModify_function
BeginForeignInsert_function
BeginForeignModify_function
--
2.46.0.519.g2e7b89e038
--gpbnw6zzq3spol54
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="v1-0007-bufmgr-Make-it-easier-to-change-number-of-buffer-.patch"
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Subject: Re: [PATCH v1 06/14] heapam: Add batch mode mvcc check and use it in page mode
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