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Get rid of WALBufMappingLock

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Allow multiple backends to initialize WAL buffers concurrently.  This way
`MemSet((char *) NewPage, 0, XLOG_BLCKSZ);` can run in parallel without
taking a single LWLock in exclusive mode.

The new algorithm works as follows:
 * reserve a page for initialization using XLogCtl->InitializeReserved,
 * ensure the page is written out,
 * once the page is initialized, try to advance XLogCtl->InitializedUpTo and
   signal to waiters using XLogCtl->InitializedUpToCondVar condition
   variable,
 * repeat previous steps until we reserve initialization up to the target
   WAL position,
 * wait until concurrent initialization finishes using a
   XLogCtl->InitializedUpToCondVar.

Now, multiple backends can, in parallel, concurrently reserve pages,
initialize them, and advance XLogCtl->InitializedUpTo to point to the latest
initialized page.

Author: Yura Sokolov <y.sokolov@postgrespro.ru>
Co-authored-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Pavel Borisov <pashkin.elfe@gmail.com>
This commit is contained in:
Alexander Korotkov
2025-02-17 04:19:01 +02:00
parent fbc0fe9a2e
commit 6a2275b895
3 changed files with 132 additions and 48 deletions
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2
src/include/storage/lwlocklist.h
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@@ -37,7 +37,7 @@ PG_LWLOCK(3, XidGen)
PG_LWLOCK(4, ProcArray)
PG_LWLOCK(5, SInvalRead)
PG_LWLOCK(6, SInvalWrite)
PG_LWLOCK(7, WALBufMapping)
/* 7 was WALBufMapping */
PG_LWLOCK(8, WALWrite)
PG_LWLOCK(9, ControlFile)
/* 10 was CheckpointLock */