diff options
| -rw-r--r-- | contrib/pg_buffercache/Makefile | 2 | ||||
| -rw-r--r-- | contrib/pg_buffercache/meson.build | 1 | ||||
| -rw-r--r-- | contrib/pg_buffercache/pg_buffercache--1.4--1.5.sql | 6 | ||||
| -rw-r--r-- | contrib/pg_buffercache/pg_buffercache.control | 2 | ||||
| -rw-r--r-- | contrib/pg_buffercache/pg_buffercache_pages.c | 20 | ||||
| -rw-r--r-- | doc/src/sgml/pgbuffercache.sgml | 39 | ||||
| -rw-r--r-- | src/backend/storage/buffer/bufmgr.c | 63 | ||||
| -rw-r--r-- | src/include/storage/bufmgr.h | 2 |
8 files changed, 127 insertions, 8 deletions
diff --git a/contrib/pg_buffercache/Makefile b/contrib/pg_buffercache/Makefile index d6b58d4da94..eae65ead9e5 100644 --- a/contrib/pg_buffercache/Makefile +++ b/contrib/pg_buffercache/Makefile @@ -8,7 +8,7 @@ OBJS = \ EXTENSION = pg_buffercache DATA = pg_buffercache--1.2.sql pg_buffercache--1.2--1.3.sql \ pg_buffercache--1.1--1.2.sql pg_buffercache--1.0--1.1.sql \ - pg_buffercache--1.3--1.4.sql + pg_buffercache--1.3--1.4.sql pg_buffercache--1.4--1.5.sql PGFILEDESC = "pg_buffercache - monitoring of shared buffer cache in real-time" REGRESS = pg_buffercache diff --git a/contrib/pg_buffercache/meson.build b/contrib/pg_buffercache/meson.build index c86e33cc958..1ca3452918b 100644 --- a/contrib/pg_buffercache/meson.build +++ b/contrib/pg_buffercache/meson.build @@ -22,6 +22,7 @@ install_data( 'pg_buffercache--1.2--1.3.sql', 'pg_buffercache--1.2.sql', 'pg_buffercache--1.3--1.4.sql', + 'pg_buffercache--1.4--1.5.sql', 'pg_buffercache.control', kwargs: contrib_data_args, ) diff --git a/contrib/pg_buffercache/pg_buffercache--1.4--1.5.sql b/contrib/pg_buffercache/pg_buffercache--1.4--1.5.sql new file mode 100644 index 00000000000..0fb18ff786d --- /dev/null +++ b/contrib/pg_buffercache/pg_buffercache--1.4--1.5.sql @@ -0,0 +1,6 @@ +\echo Use "ALTER EXTENSION pg_buffercache UPDATE TO '1.5'" to load this file. \quit + +CREATE FUNCTION pg_buffercache_evict(IN int) +RETURNS bool +AS 'MODULE_PATHNAME', 'pg_buffercache_evict' +LANGUAGE C PARALLEL SAFE VOLATILE STRICT; diff --git a/contrib/pg_buffercache/pg_buffercache.control b/contrib/pg_buffercache/pg_buffercache.control index a82ae5f9bb5..5ee875f77dd 100644 --- a/contrib/pg_buffercache/pg_buffercache.control +++ b/contrib/pg_buffercache/pg_buffercache.control @@ -1,5 +1,5 @@ # pg_buffercache extension comment = 'examine the shared buffer cache' -default_version = '1.4' +default_version = '1.5' module_pathname = '$libdir/pg_buffercache' relocatable = true diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c index 33167323653..3ae0a018e10 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -63,6 +63,7 @@ typedef struct PG_FUNCTION_INFO_V1(pg_buffercache_pages); PG_FUNCTION_INFO_V1(pg_buffercache_summary); PG_FUNCTION_INFO_V1(pg_buffercache_usage_counts); +PG_FUNCTION_INFO_V1(pg_buffercache_evict); Datum pg_buffercache_pages(PG_FUNCTION_ARGS) @@ -347,3 +348,22 @@ pg_buffercache_usage_counts(PG_FUNCTION_ARGS) return (Datum) 0; } + +/* + * Try to evict a shared buffer. + */ +Datum +pg_buffercache_evict(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_evict function"))); + + if (buf < 1 || buf > NBuffers) + elog(ERROR, "bad buffer ID: %d", buf); + + PG_RETURN_BOOL(EvictUnpinnedBuffer(buf)); +} diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml index afe2d978340..4b90eefc0b0 100644 --- a/doc/src/sgml/pgbuffercache.sgml +++ b/doc/src/sgml/pgbuffercache.sgml @@ -11,6 +11,8 @@ <para> The <filename>pg_buffercache</filename> module provides a means for examining what's happening in the shared buffer cache in real time. + It also offers a low-level way to evict data from it, for testing + purposes. </para> <indexterm> @@ -21,11 +23,16 @@ <primary>pg_buffercache_summary</primary> </indexterm> + <indexterm> + <primary>pg_buffercache_evict</primary> + </indexterm> + <para> This module provides the <function>pg_buffercache_pages()</function> function (wrapped in the <structname>pg_buffercache</structname> view), - the <function>pg_buffercache_summary()</function> function, and the - <function>pg_buffercache_usage_counts()</function> function. + the <function>pg_buffercache_summary()</function> function, the + <function>pg_buffercache_usage_counts()</function> function and + the <function>pg_buffercache_evict()</function> function. </para> <para> @@ -47,9 +54,15 @@ </para> <para> - By default, use is restricted to superusers and roles with privileges of the - <literal>pg_monitor</literal> role. Access may be granted to others - using <command>GRANT</command>. + By default, use of the above functions is restricted to superusers and roles + with privileges of the <literal>pg_monitor</literal> role. Access may be + granted to others using <command>GRANT</command>. + </para> + + <para> + The <function>pg_buffercache_evict()</function> function allows a block to + be evicted from the buffer pool given a buffer identifier. Use of this + function is restricted to superusers only. </para> <sect2 id="pgbuffercache-pg-buffercache"> @@ -351,7 +364,21 @@ </para> </sect2> - <sect2 id="pgbuffercache-sample-output"> + <sect2 id="pgbuffercache-pg-buffercache-evict"> + <title>The <structname>pg_buffercache_evict</structname> Function</title> + <para> + The <function>pg_buffercache_evict()</function> function takes a buffer + identifier, as shown in the <structfield>bufferid</structfield> column of + the <structname>pg_buffercache</structname> view. It returns true on success, + and false if the buffer wasn't valid, if it couldn't be evicted because it + was pinned, or if it became dirty again after an attempt to write it out. + The result is immediately out of date upon return, as the buffer might + become valid again at any time due to concurrent activity. The function is + intended for developer testing only. + </para> + </sect2> + +<sect2 id="pgbuffercache-sample-output"> <title>Sample Output</title> <screen> diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 06e9ffd2b00..44836751b71 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -6003,3 +6003,66 @@ ResOwnerPrintBufferPin(Datum res) { return DebugPrintBufferRefcount(DatumGetInt32(res)); } + +/* + * Try to evict the current block in a shared buffer. + * + * 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 again by the time control is returned, potentially + * even by the same block. This inherent raciness without other interlocking + * makes the function unsuitable for non-testing usage. + * + * Returns true if the buffer was valid and it has now been made invalid. + * Returns false if it wasn't valid, if it couldn't be evicted due to a pin, + * or if the buffer becomes dirty again while we're trying to write it out. + */ +bool +EvictUnpinnedBuffer(Buffer buf) +{ + BufferDesc *desc; + uint32 buf_state; + bool result; + + /* Make sure we can pin the buffer. */ + ResourceOwnerEnlarge(CurrentResourceOwner); + ReservePrivateRefCountEntry(); + + Assert(!BufferIsLocal(buf)); + 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 dirty, try to clean it once. */ + if (buf_state & BM_DIRTY) + { + LWLockAcquire(BufferDescriptorGetContentLock(desc), LW_SHARED); + FlushBuffer(desc, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL); + LWLockRelease(BufferDescriptorGetContentLock(desc)); + } + + /* This will return false if it becomes dirty or someone else pins it. */ + result = InvalidateVictimBuffer(desc); + + UnpinBuffer(desc); + + return result; +} diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index 07ba1a60502..42211bfec4f 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -305,6 +305,8 @@ extern bool BgBufferSync(struct WritebackContext *wb_context); extern void LimitAdditionalPins(uint32 *additional_pins); extern void LimitAdditionalLocalPins(uint32 *additional_pins); +extern bool EvictUnpinnedBuffer(Buffer buf); + /* in buf_init.c */ extern void InitBufferPool(void); extern Size BufferShmemSize(void); |