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Commit82a4eda

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hio: Take number of prior relation extensions into account
The new relation extension logic, introduced in00d1e02, could lead toslowdowns in some scenarios. E.g., when loading narrow rows into a table usingCOPY, the caller of RelationGetBufferForTuple() will only request a smallnumber of pages. Without concurrency, we just extended using pwritev() in thatcase. However, if there is *some* concurrency, we switched between extendingby a small number of pages and a larger number of pages, depending on thenumber of waiters for the relation extension logic. However, somefilesystems, XFS in particular, do not perform well when switching betweenextending files using fallocate() and pwritev().To avoid that issue, remember the number of prior relation extensions inBulkInsertState and extend more aggressively if there were prior relationextensions. That not just avoids the aforementioned slowdown, but also leadsto noticeable performance gains in other situations, primarily due toextending more aggressively when there is no concurrency. I should have doneit this way from the get go.Reported-by: Masahiko Sawada <sawada.mshk@gmail.com>Author: Andres Freund <andres@anarazel.de>Discussion:https://postgr.es/m/CAD21AoDvDmUQeJtZrau1ovnT_smN940=Kp6mszNGK3bq9yRN6g@mail.gmail.comBackpatch: 16-, where the new relation extension code was added
1 parent94f9c08 commit82a4eda

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3 files changed

+30
-3
lines changed

3 files changed

+30
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‎src/backend/access/heap/heapam.c

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@@ -1776,6 +1776,7 @@ GetBulkInsertState(void)
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bistate->current_buf=InvalidBuffer;
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bistate->next_free=InvalidBlockNumber;
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bistate->last_free=InvalidBlockNumber;
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bistate->already_extended_by=0;
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returnbistate;
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}
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‎src/backend/access/heap/hio.c

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@@ -283,6 +283,24 @@ RelationAddBlocks(Relation relation, BulkInsertState bistate,
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*/
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extend_by_pages+=extend_by_pages*waitcount;
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/* ---
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* If we previously extended using the same bistate, it's very likely
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* we'll extend some more. Try to extend by as many pages as
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* before. This can be important for performance for several reasons,
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* including:
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*
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* - It prevents mdzeroextend() switching between extending the
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* relation in different ways, which is inefficient for some
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* filesystems.
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*
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* - Contention is often intermittent. Even if we currently don't see
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* other waiters (see above), extending by larger amounts can
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* prevent future contention.
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* ---
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*/
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if (bistate)
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extend_by_pages=Max(extend_by_pages,bistate->already_extended_by);
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/*
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* Can't extend by more than MAX_BUFFERS_TO_EXTEND_BY, we need to pin
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* them all concurrently.
@@ -409,6 +427,7 @@ RelationAddBlocks(Relation relation, BulkInsertState bistate,
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/* maintain bistate->current_buf */
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IncrBufferRefCount(buffer);
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bistate->current_buf=buffer;
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bistate->already_extended_by+=extend_by_pages;
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}
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returnbuffer;

‎src/include/access/hio.h

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Original file line numberDiff line numberDiff line change
@@ -32,15 +32,22 @@ typedef struct BulkInsertStateData
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Buffercurrent_buf;/* current insertion target page */
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/*
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* State for bulk extensions. Further pages that were unused at the time
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* of the extension. They might be in use by the time we use them though,
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* so rechecks are needed.
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* State for bulk extensions.
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*
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* last_free..next_free are further pages that were unused at the time of
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* the last extension. They might be in use by the time we use them
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* though, so rechecks are needed.
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*
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* XXX: Eventually these should probably live in RelationData instead,
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* alongside targetblock.
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*
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* already_extended_by is the number of pages that this bulk inserted
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* extended by. If we already extended by a significant number of pages,
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* we can be more aggressive about extending going forward.
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*/
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BlockNumbernext_free;
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BlockNumberlast_free;
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uint32already_extended_by;
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}BulkInsertStateData;
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