From 642e563a1aa8a4c27be2792dde558730edc79900 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Mon, 8 Apr 2024 19:59:45 +1200 Subject: [PATCH v7 3/3] Use contiguous memory for bulk_write.c. Instead of allocating buffers one at a time with palloc(), allocate an array full of them up front, and then manage them in a FIFO freelist. Aside from avoiding repeated allocator overheads, this means that callers that tend to write sequential blocks will tend to fill up sequential memory, which hopefully generates more efficient vectored writes or simple non-vectored writes. This implements an idea described in the comments of commit 8af25652. Reviewed-by: Heikki Linnakangas Discussion: https://postgr.es/m/CA%2BhUKGLx5bLwezZKAYB2O_qHj%3Dov10RpgRVY7e8TSJVE74oVjg%40mail.gmail.com --- src/backend/storage/smgr/bulk_write.c | 66 +++++++++++++++++++-------- src/tools/pgindent/typedefs.list | 1 + 2 files changed, 48 insertions(+), 19 deletions(-) diff --git a/src/backend/storage/smgr/bulk_write.c b/src/backend/storage/smgr/bulk_write.c index 45d66245860..6d16619f6be 100644 --- a/src/backend/storage/smgr/bulk_write.c +++ b/src/backend/storage/smgr/bulk_write.c @@ -36,6 +36,7 @@ #include "access/xloginsert.h" #include "access/xlogrecord.h" +#include "lib/ilist.h" #include "storage/bufmgr.h" #include "storage/bufpage.h" #include "storage/bulk_write.h" @@ -47,9 +48,15 @@ static const PGIOAlignedBlock zero_buffer = {{0}}; /* worth BLCKSZ */ +typedef union BufferSlot +{ + PGIOAlignedBlock buffer; + dlist_node freelist_node; +} BufferSlot; + typedef struct PendingWrite { - BulkWriteBuffer buf; + BufferSlot *slot; BlockNumber blkno; bool page_std; } PendingWrite; @@ -59,6 +66,14 @@ typedef struct PendingWrite */ struct BulkWriteState { + /* + * This must come first so that it is correctly aligned for I/O. We have + * one extra slot for the write that has been allocated but not yet + * submitted to smgr_bulk_write() yet. + */ + BufferSlot buffer_slots[MAX_PENDING_WRITES + 1]; + dlist_head buffer_slots_freelist; + /* Information about the target relation we're writing */ SMgrRelation smgr; ForkNumber forknum; @@ -73,8 +88,6 @@ struct BulkWriteState /* The RedoRecPtr at the time that the bulk operation started */ XLogRecPtr start_RedoRecPtr; - - MemoryContext memcxt; }; static void smgr_bulk_flush(BulkWriteState *bulkstate); @@ -100,7 +113,7 @@ smgr_bulk_start_smgr(SMgrRelation smgr, ForkNumber forknum, bool use_wal) { BulkWriteState *state; - state = palloc(sizeof(BulkWriteState)); + state = palloc_aligned(sizeof(BulkWriteState), PG_IO_ALIGN_SIZE, 0); state->smgr = smgr; state->forknum = forknum; state->use_wal = use_wal; @@ -110,11 +123,11 @@ smgr_bulk_start_smgr(SMgrRelation smgr, ForkNumber forknum, bool use_wal) state->start_RedoRecPtr = GetRedoRecPtr(); - /* - * Remember the memory context. We will use it to allocate all the - * buffers later. - */ - state->memcxt = CurrentMemoryContext; + /* Set up the free-list of buffers. */ + dlist_init(&state->buffer_slots_freelist); + for (int i = 0; i < lengthof(state->buffer_slots); ++i) + dlist_push_tail(&state->buffer_slots_freelist, + &state->buffer_slots[i].freelist_node); return state; } @@ -208,7 +221,7 @@ smgr_bulk_flush(BulkWriteState *bulkstate) for (int i = 0; i < npending; i++) { blknos[i] = pending_writes[i].blkno; - pages[i] = pending_writes[i].buf->data; + pages[i] = pending_writes[i].slot->buffer.data; /* * If any of the pages use !page_std, we log them all as such. @@ -233,7 +246,7 @@ smgr_bulk_flush(BulkWriteState *bulkstate) /* Prepare to write the first block. */ blkno = pending_writes[i].blkno; - page = pending_writes[i].buf->data; + page = pending_writes[i].slot->buffer.data; PageSetChecksumInplace(page, blkno); pages[0] = page; nblocks = 1; @@ -275,7 +288,7 @@ smgr_bulk_flush(BulkWriteState *bulkstate) pending_writes[i + 1].blkno == blkno + nblocks && nblocks < max_nblocks) { - page = pending_writes[++i].buf->data; + page = pending_writes[++i].slot->buffer.data; PageSetChecksumInplace(page, pending_writes[i].blkno); pages[nblocks++] = page; } @@ -296,8 +309,14 @@ smgr_bulk_flush(BulkWriteState *bulkstate) SMGR_WRITE_SKIP_FSYNC); } - for (int j = 0; j < nblocks; ++j) - pfree(pending_writes[i - j].buf->data); + /* + * Maintain FIFO ordering in the free list, so that users who write + * blocks in sequential order tend to get sequential chunks of buffer + * memory, which may be slight more efficient for vectored writes. + */ + for (int j = i - nblocks + 1; j <= i; ++j) + dlist_push_tail(&bulkstate->buffer_slots_freelist, + &pending_writes[j].slot->freelist_node); } bulkstate->npending = 0; @@ -317,7 +336,7 @@ smgr_bulk_write(BulkWriteState *bulkstate, BlockNumber blocknum, BulkWriteBuffer PendingWrite *w; w = &bulkstate->pending_writes[bulkstate->npending++]; - w->buf = buf; + w->slot = (BufferSlot *) buf; w->blkno = blocknum; w->page_std = page_std; @@ -332,12 +351,21 @@ smgr_bulk_write(BulkWriteState *bulkstate, BlockNumber blocknum, BulkWriteBuffer * There is no function to free the buffer. When you pass it to * smgr_bulk_write(), it takes ownership and frees it when it's no longer * needed. - * - * This is currently implemented as a simple palloc, but could be implemented - * using a ring buffer or larger chunks in the future, so don't rely on it. */ BulkWriteBuffer smgr_bulk_get_buf(BulkWriteState *bulkstate) { - return MemoryContextAllocAligned(bulkstate->memcxt, BLCKSZ, PG_IO_ALIGN_SIZE, 0); + BufferSlot *slot; + + if (dlist_is_empty(&bulkstate->buffer_slots_freelist)) + { + smgr_bulk_flush(bulkstate); + if (dlist_is_empty(&bulkstate->buffer_slots_freelist)) + elog(ERROR, "too many bulk write buffers used but not yet written"); + } + + slot = dlist_head_element(BufferSlot, freelist_node, &bulkstate->buffer_slots_freelist); + dlist_pop_head_node(&bulkstate->buffer_slots_freelist); + + return &slot->buffer; } diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index 704e61dcaa2..05669916c78 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -328,6 +328,7 @@ BufferDescPadded BufferHeapTupleTableSlot BufferLookupEnt BufferManagerRelation +BufferSlot BufferStrategyControl BufferTag BufferUsage -- 2.44.0