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Commitf5930f9

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Improve accounting for memory used by shared hash tables
pg_shmem_allocations tracks the memory allocated by ShmemInitStruct(),but for shared hash tables that covered only the header and hashdirectory. The remaining parts (segments and buckets) were allocatedlater using ShmemAlloc(), which does not update the shmem accounting.Thus, these allocations were not shown in pg_shmem_allocations.This commit improves the situation by allocating all the hash tableparts at once, using a single ShmemInitStruct() call. This way theShmemIndex entries (and thus pg_shmem_allocations) better reflect theproper size of the hash table.This affects allocations for private (non-shared) hash tables too, asthe hash_create() code is shared. For non-shared tables this howevermakes no practical difference.This changes the alignment a bit. ShmemAlloc() aligns the chunks usingCACHELINEALIGN(), which means some parts (header, directory, segments)were aligned this way. Allocating all parts as a single chunk removesthis (implicit) alignment. We've considered adding explicit alignment,but we've decided not to - it seems to be merely a coincidence due tousing the ShmemAlloc() API, not due to necessity.Author: Rahila Syed <rahilasyed90@gmail.com>Reviewed-by: Andres Freund <andres@anarazel.de>Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>Reviewed-by: Tomas Vondra <tomas@vondra.me>Discussion:https://postgr.es/m/CAH2L28vHzRankszhqz7deXURxKncxfirnuW68zD7+hVAqaS5GQ@mail.gmail.com
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3 files changed

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3 files changed

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‎src/backend/storage/ipc/shmem.c‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -73,6 +73,7 @@
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#include"storage/shmem.h"
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#include"storage/spin.h"
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#include"utils/builtins.h"
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#include"utils/dynahash.h"
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staticvoid*ShmemAllocRaw(Sizesize,Size*allocated_size);
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@@ -346,7 +347,8 @@ ShmemInitHash(const char *name,/* table string name for shmem index */
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/* look it up in the shmem index */
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location=ShmemInitStruct(name,
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hash_get_shared_size(infoP,hash_flags),
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hash_get_size(infoP,hash_flags,
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init_size, true),
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&found);
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/*

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