From 05ce938fef85a5f23407d6977165319650b05d63 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Thu, 25 Mar 2021 10:11:31 +1300 Subject: [PATCH v14 1/2] Add a buffer mapping table for SLRUs. Instead of doing a linear search for the buffer holding a given page number, use a hash table. This will allow us to increase the size of these caches. Reviewed-by: Andrey M. Borodin Discussion: https://postgr.es/m/2BEC2B3F-9B61-4C1D-9FB5-5FAB0F05EF86%40yandex-team.ru --- src/backend/access/transam/slru.c | 110 +++++++++++++++++++++++++----- src/include/access/slru.h | 2 + 2 files changed, 95 insertions(+), 17 deletions(-) diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c index 82149ad782..a88e7a38a3 100644 --- a/src/backend/access/transam/slru.c +++ b/src/backend/access/transam/slru.c @@ -58,6 +58,7 @@ #include "pgstat.h" #include "storage/fd.h" #include "storage/shmem.h" +#include "utils/hsearch.h" #define SlruFileName(ctl, path, seg) \ snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir, seg) @@ -79,6 +80,12 @@ typedef struct SlruWriteAllData typedef struct SlruWriteAllData *SlruWriteAll; +typedef struct SlruMappingTableEntry +{ + int pageno; + int slotno; +} SlruMappingTableEntry; + /* * Populate a file tag describing a segment file. We only use the segment * number, since we can derive everything else we need by having separate @@ -146,6 +153,9 @@ static int SlruSelectLRUPage(SlruCtl ctl, int pageno); static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data); static void SlruInternalDeleteSegment(SlruCtl ctl, int segno); +static void SlruMappingAdd(SlruCtl ctl, int pageno, int slotno); +static void SlruMappingRemove(SlruCtl ctl, int pageno); +static int SlruMappingFind(SlruCtl ctl, int pageno); /* * Initialization of shared memory @@ -168,7 +178,8 @@ SimpleLruShmemSize(int nslots, int nlsns) if (nlsns > 0) sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); /* group_lsn[] */ - return BUFFERALIGN(sz) + BLCKSZ * nslots; + return BUFFERALIGN(sz) + BLCKSZ * nslots + + hash_estimate_size(nslots, sizeof(SlruMappingTableEntry)); } /* @@ -187,6 +198,9 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, LWLock *ctllock, const char *subdir, int tranche_id, SyncRequestHandler sync_handler) { + char mapping_table_name[SHMEM_INDEX_KEYSIZE]; + HASHCTL mapping_table_info; + HTAB *mapping_table; SlruShared shared; bool found; @@ -258,11 +272,21 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, else Assert(found); + /* Create or find the buffer mapping table. */ + memset(&mapping_table_info, 0, sizeof(mapping_table_info)); + mapping_table_info.keysize = sizeof(int); + mapping_table_info.entrysize = sizeof(SlruMappingTableEntry); + snprintf(mapping_table_name, sizeof(mapping_table_name), + "%s Lookup Table", name); + mapping_table = ShmemInitHash(mapping_table_name, nslots, nslots, + &mapping_table_info, HASH_ELEM | HASH_BLOBS); + /* * Initialize the unshared control struct, including directory path. We * assume caller set PagePrecedes. */ ctl->shared = shared; + ctl->mapping_table = mapping_table; ctl->sync_handler = sync_handler; strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir)); } @@ -289,6 +313,9 @@ SimpleLruZeroPage(SlruCtl ctl, int pageno) shared->page_number[slotno] == pageno); /* Mark the slot as containing this page */ + if (shared->page_status[slotno] != SLRU_PAGE_EMPTY) + SlruMappingRemove(ctl, shared->page_number[slotno]); + SlruMappingAdd(ctl, pageno, slotno); shared->page_number[slotno] = pageno; shared->page_status[slotno] = SLRU_PAGE_VALID; shared->page_dirty[slotno] = true; @@ -362,7 +389,10 @@ SimpleLruWaitIO(SlruCtl ctl, int slotno) { /* indeed, the I/O must have failed */ if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS) + { + SlruMappingRemove(ctl, shared->page_number[slotno]); shared->page_status[slotno] = SLRU_PAGE_EMPTY; + } else /* write_in_progress */ { shared->page_status[slotno] = SLRU_PAGE_VALID; @@ -436,6 +466,9 @@ SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok, !shared->page_dirty[slotno])); /* Mark the slot read-busy */ + if (shared->page_status[slotno] != SLRU_PAGE_EMPTY) + SlruMappingRemove(ctl, shared->page_number[slotno]); + SlruMappingAdd(ctl, pageno, slotno); shared->page_number[slotno] = pageno; shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS; shared->page_dirty[slotno] = false; @@ -459,7 +492,13 @@ SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok, shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS && !shared->page_dirty[slotno]); - shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY; + if (ok) + shared->page_status[slotno] = SLRU_PAGE_VALID; + else + { + SlruMappingRemove(ctl, pageno); + shared->page_status[slotno] = SLRU_PAGE_EMPTY; + } LWLockRelease(&shared->buffer_locks[slotno].lock); @@ -500,20 +539,20 @@ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid) LWLockAcquire(shared->ControlLock, LW_SHARED); /* See if page is already in a buffer */ - for (slotno = 0; slotno < shared->num_slots; slotno++) + slotno = SlruMappingFind(ctl, pageno); + if (slotno >= 0 && + shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS) { - if (shared->page_number[slotno] == pageno && - shared->page_status[slotno] != SLRU_PAGE_EMPTY && - shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS) - { - /* See comments for SlruRecentlyUsed macro */ - SlruRecentlyUsed(shared, slotno); + Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY); + Assert(shared->page_number[slotno] == pageno); - /* update the stats counter of pages found in the SLRU */ - pgstat_count_slru_page_hit(shared->slru_stats_idx); + /* See comments for SlruRecentlyUsed macro */ + SlruRecentlyUsed(shared, slotno); - return slotno; - } + /* update the stats counter of pages found in the SLRU */ + pgstat_count_slru_page_hit(shared->slru_stats_idx); + + return slotno; } /* No luck, so switch to normal exclusive lock and do regular read */ @@ -1029,11 +1068,12 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno) int best_invalid_page_number = 0; /* keep compiler quiet */ /* See if page already has a buffer assigned */ - for (slotno = 0; slotno < shared->num_slots; slotno++) + slotno = SlruMappingFind(ctl, pageno); + if (slotno >= 0) { - if (shared->page_number[slotno] == pageno && - shared->page_status[slotno] != SLRU_PAGE_EMPTY) - return slotno; + Assert(shared->page_number[slotno] == pageno); + Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY); + return slotno; } /* @@ -1266,6 +1306,7 @@ restart:; if (shared->page_status[slotno] == SLRU_PAGE_VALID && !shared->page_dirty[slotno]) { + SlruMappingRemove(ctl, shared->page_number[slotno]); shared->page_status[slotno] = SLRU_PAGE_EMPTY; continue; } @@ -1348,6 +1389,7 @@ restart: if (shared->page_status[slotno] == SLRU_PAGE_VALID && !shared->page_dirty[slotno]) { + SlruMappingRemove(ctl, shared->page_number[slotno]); shared->page_status[slotno] = SLRU_PAGE_EMPTY; continue; } @@ -1609,3 +1651,37 @@ SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path) errno = save_errno; return result; } + +static int +SlruMappingFind(SlruCtl ctl, int pageno) +{ + SlruMappingTableEntry *mapping; + + mapping = hash_search(ctl->mapping_table, &pageno, HASH_FIND, NULL); + if (mapping) + return mapping->slotno; + + return -1; +} + +static void +SlruMappingAdd(SlruCtl ctl, int pageno, int slotno) +{ + SlruMappingTableEntry *mapping; + bool found PG_USED_FOR_ASSERTS_ONLY; + + mapping = hash_search(ctl->mapping_table, &pageno, HASH_ENTER, &found); + mapping->slotno = slotno; + + Assert(!found); +} + +static void +SlruMappingRemove(SlruCtl ctl, int pageno) +{ + bool found PG_USED_FOR_ASSERTS_ONLY; + + hash_search(ctl->mapping_table, &pageno, HASH_REMOVE, &found); + + Assert(found); +} diff --git a/src/include/access/slru.h b/src/include/access/slru.h index dd52e8cec7..8aa3efc0ee 100644 --- a/src/include/access/slru.h +++ b/src/include/access/slru.h @@ -16,6 +16,7 @@ #include "access/xlogdefs.h" #include "storage/lwlock.h" #include "storage/sync.h" +#include "utils/hsearch.h" /* @@ -110,6 +111,7 @@ typedef SlruSharedData *SlruShared; typedef struct SlruCtlData { SlruShared shared; + HTAB *mapping_table; /* * Which sync handler function to use when handing sync requests over to -- 2.30.2