From 99354adda53d07d28940810b429648a855eeaf12 Mon Sep 17 00:00:00 2001 From: Soumya Date: Fri, 23 Jan 2026 12:24:11 +0530 Subject: [PATCH] Batch buffer writebacks during checkpoints Signed-off-by: Soumya --- src/backend/storage/buffer/bufmgr.c | 77 ++++++++++++++++++++++++++--- 1 file changed, 71 insertions(+), 6 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 6f935648ae9..c92d638f804 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -3467,6 +3467,15 @@ BufferSync(int flags) int i; uint64 mask = BM_DIRTY; WritebackContext wb_context; + uint64 ckpt_write_count = 0; + uint64 ckpt_issue_writeback_calls = 0; + + /* --- checkpoint write batching --- */ + #define CHECKPOINT_WRITE_BATCH 16 + + int batch_bufs[CHECKPOINT_WRITE_BATCH]; + int batch_count = 0; + /* --- checkpoint write batching --- */ /* * Unless this is a shutdown checkpoint or we have been explicitly told, @@ -3666,12 +3675,37 @@ BufferSync(int flags) */ if (pg_atomic_read_u64(&bufHdr->state) & BM_CHECKPOINT_NEEDED) { - if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN) - { - TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id); - PendingCheckpointerStats.buffers_written++; - num_written++; - } + /* + * Collect buffer into a small local batch. + * Phase 1: batch size is 1, so this is behavior-neutral. + */ + batch_bufs[batch_count++] = buf_id; + + /* + * Flush batch if full. + */ + if (batch_count == CHECKPOINT_WRITE_BATCH) + { + int j; + + for (j = 0; j < batch_count; j++) + { + if (SyncOneBuffer(batch_bufs[j], false, &wb_context) & BUF_WRITTEN) + { + TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(batch_bufs[j]); + PendingCheckpointerStats.buffers_written++; + num_written++; + ckpt_write_count++; + } + } + /* + * Issue writeback for this batch to amortize syscall cost. + * This does NOT change durability semantics. + */ + ckpt_issue_writeback_calls++; + IssuePendingWritebacks(&wb_context, IOCONTEXT_NORMAL); + batch_count = 0; + } } /* @@ -3701,6 +3735,31 @@ BufferSync(int flags) CheckpointWriteDelay(flags, (double) num_processed / num_to_scan); } + /* + * Flush any remaining buffers in the batch. + */ + if (batch_count > 0) + { + int j; + + for (j = 0; j < batch_count; j++) + { + if (SyncOneBuffer(batch_bufs[j], false, &wb_context) & BUF_WRITTEN) + { + TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(batch_bufs[j]); + PendingCheckpointerStats.buffers_written++; + num_written++; + ckpt_write_count++; + } + } + ckpt_issue_writeback_calls++; + IssuePendingWritebacks(&wb_context, IOCONTEXT_NORMAL); + batch_count = 0; + } + + /* --- checkpoint instrumentation --- */ + ckpt_issue_writeback_calls++; + /* * Issue all pending flushes. Only checkpointer calls BufferSync(), so * IOContext will always be IOCONTEXT_NORMAL. @@ -3717,6 +3776,12 @@ BufferSync(int flags) */ CheckpointStats.ckpt_bufs_written += num_written; + ereport(DEBUG1, + (errmsg("checkpoint BufferSync stats: buffers_written=%lu, " + "writeback_calls=%lu", + ckpt_write_count, + ckpt_issue_writeback_calls))); + TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_scan); } -- 2.34.1