From 19b0a56e72525ee1c9754fb06ab5f31d41e43ca7 Mon Sep 17 00:00:00 2001 From: Nazir Bilal Yavuz Date: Wed, 25 Dec 2024 15:46:10 +0300 Subject: [PATCH v1 2/2] Add pg_buffercache_mark_dirty[_all]() functions for testing This commit introduces two new functions for marking shared buffers as dirty: pg_buffercache_mark_dirty(): Marks a specific shared buffer as dirty. pg_buffercache_mark_dirty_all(): Marks all shared buffers as dirty in a single operation. The pg_buffercache_mark_dirty_all() function provides an efficient way to dirty the entire buffer pool (e.g., ~550ms vs. ~70ms for 16GB of shared buffers), complementing pg_buffercache_mark_dirty() for more granular control. These functions are intended for developer testing and debugging scenarios, enabling users to simulate various buffer pool states and test write-back behavior. Both functions are superuser-only. --- src/include/storage/bufmgr.h | 1 + src/backend/storage/buffer/bufmgr.c | 62 +++++++++++++++++++ doc/src/sgml/pgbuffercache.sgml | 40 +++++++++++- .../pg_buffercache--1.5--1.6.sql | 10 +++ contrib/pg_buffercache/pg_buffercache_pages.c | 43 +++++++++++++ 5 files changed, 154 insertions(+), 2 deletions(-) diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 7f4eeca4afd..ac077402dd9 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -298,6 +298,7 @@ extern void LimitAdditionalPins(uint32 *additional_pins); extern void LimitAdditionalLocalPins(uint32 *additional_pins); extern bool EvictUnpinnedBuffer(Buffer buf, bool *flushed); +extern bool MarkUnpinnedBufferDirty(Buffer buf); /* in buf_init.c */ extern void BufferManagerShmemInit(void); diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index d2a93cf7cc0..7ab8bcaa228 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -6146,3 +6146,65 @@ EvictUnpinnedBuffer(Buffer buf, bool *flushed) return result; } + +/* + * MarkUnpinnedBufferDirty + * + * This function is intended for testing/development use only! + * + * To succeed, the buffer must not be pinned on entry, so if the caller had a + * particular block in mind, it might already have been replaced by some other + * block by the time this function runs. It's also unpinned on return, so the + * buffer might be occupied and flushed by the time control is returned. This + * inherent raciness without other interlocking makes the function unsuitable + * for non-testing usage. + * + * Returns true if the buffer was not dirty and it has now been marked as + * dirty. Returns false if it wasn't valid, if it couldn't be marked as dirty + * due to a pin, or if the buffer was already dirty. + */ +bool +MarkUnpinnedBufferDirty(Buffer buf) +{ + BufferDesc *desc; + uint32 buf_state; + bool result = false; + + Assert(!BufferIsLocal(buf)); + + /* Make sure we can pin the buffer. */ + ResourceOwnerEnlarge(CurrentResourceOwner); + ReservePrivateRefCountEntry(); + + desc = GetBufferDescriptor(buf - 1); + + /* Lock the header and check if it's valid. */ + buf_state = LockBufHdr(desc); + if ((buf_state & BM_VALID) == 0) + { + UnlockBufHdr(desc, buf_state); + return false; + } + + /* Check that it's not pinned already. */ + if (BUF_STATE_GET_REFCOUNT(buf_state) > 0) + { + UnlockBufHdr(desc, buf_state); + return false; + } + + PinBuffer_Locked(desc); /* releases spinlock */ + + /* If it was not already dirty, mark it as dirty. */ + if (!(buf_state & BM_DIRTY)) + { + LWLockAcquire(BufferDescriptorGetContentLock(desc), LW_EXCLUSIVE); + MarkBufferDirty(buf); + LWLockRelease(BufferDescriptorGetContentLock(desc)); + result = true; + } + + UnpinBuffer(desc); + + return result; +} diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml index df4d90a650a..a1c5036a383 100644 --- a/doc/src/sgml/pgbuffercache.sgml +++ b/doc/src/sgml/pgbuffercache.sgml @@ -32,8 +32,10 @@ function (wrapped in the pg_buffercache view), the pg_buffercache_summary() function, the pg_buffercache_usage_counts() function, the - pg_buffercache_evict() and the - pg_buffercache_evict_all() function. + pg_buffercache_evict() the + pg_buffercache_evict_all(), the + pg_buffercache_mark_dirty() and the + pg_buffercache_mark_dirty_all() function. @@ -72,6 +74,18 @@ evicted and flushed. Use of this function is restricted to superusers only. + + The pg_buffercache_mark_dirty() function allows a block + to be marked as dirty from the buffer pool given a buffer identifier. Use of + this function is restricted to superusers only. + + + + The pg_buffercache_mark_dirty_all() function tries to + mark all buffers dirty in the buffer pool. It returns how many buffers are + dirtied. Use of this function is restricted to superusers only. + + The <structname>pg_buffercache</structname> View @@ -396,6 +410,28 @@ + + The <structname>pg_buffercache_mark_dirty</structname> Function + + The pg_buffercache_mark_dirty() function takes a buffer + identifier, as shown in the bufferid column of + the pg_buffercache view. It returns true on success, + and false if the buffer wasn't valid or if it couldn't be marked as dirty + because it was pinned. The function is intended for developer testing only. + + + + + The <structname>pg_buffercache_mark_dirty_all</structname> Function + + The pg_buffercache_mark_dirty_all() function is very similar + to pg_buffercache_mark_dirty() function. The difference is, + the pg_buffercache_mark_dirty_all() does not take argument; + instead it tries to mark all buffers dirty in the buffer pool. The function is + intended for developer testing only. + + + Sample Output diff --git a/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql b/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql index c08b799be94..e725fef1247 100644 --- a/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql +++ b/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql @@ -5,3 +5,13 @@ CREATE FUNCTION pg_buffercache_evict_all( OUT buffers_flushed int4) AS 'MODULE_PATHNAME', 'pg_buffercache_evict_all' LANGUAGE C PARALLEL SAFE VOLATILE; + +CREATE FUNCTION pg_buffercache_mark_dirty(IN int) +RETURNS bool +AS 'MODULE_PATHNAME', 'pg_buffercache_mark_dirty' +LANGUAGE C PARALLEL SAFE VOLATILE STRICT; + +CREATE FUNCTION pg_buffercache_mark_dirty_all() +RETURNS INT4 +AS 'MODULE_PATHNAME', 'pg_buffercache_mark_dirty_all' +LANGUAGE C PARALLEL SAFE VOLATILE; diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c index ea7c0e6934c..1a0992467b2 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -66,6 +66,8 @@ PG_FUNCTION_INFO_V1(pg_buffercache_summary); PG_FUNCTION_INFO_V1(pg_buffercache_usage_counts); PG_FUNCTION_INFO_V1(pg_buffercache_evict); PG_FUNCTION_INFO_V1(pg_buffercache_evict_all); +PG_FUNCTION_INFO_V1(pg_buffercache_mark_dirty); +PG_FUNCTION_INFO_V1(pg_buffercache_mark_dirty_all); Datum pg_buffercache_pages(PG_FUNCTION_ARGS) @@ -412,3 +414,44 @@ pg_buffercache_evict_all(PG_FUNCTION_ARGS) PG_RETURN_DATUM(result); } + +/* + * Try to mark dirty a shared buffer. + */ +Datum +pg_buffercache_mark_dirty(PG_FUNCTION_ARGS) +{ + Buffer buf = PG_GETARG_INT32(0); + + if (!superuser()) + ereport(ERROR, + (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), + errmsg("must be superuser to use pg_buffercache_mark_dirty function"))); + + if (buf < 1 || buf > NBuffers) + elog(ERROR, "bad buffer ID: %d", buf); + + PG_RETURN_BOOL(MarkUnpinnedBufferDirty(buf)); +} + +/* + * Try to mark dirty all shared buffers. + */ +Datum +pg_buffercache_mark_dirty_all(PG_FUNCTION_ARGS) +{ + int32 buffers_dirtied = 0; + + if (!superuser()) + ereport(ERROR, + (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), + errmsg("must be superuser to use pg_buffercache_mark_dirty_all function"))); + + for (int buf = 1; buf < NBuffers; buf++) + { + if (MarkUnpinnedBufferDirty(buf)) + buffers_dirtied++; + } + + PG_RETURN_INT32(buffers_dirtied); +} -- 2.45.2