[Sorry to those who received this message twice -- the first time got
bounced by the list because of a defunct email address in the CC
list.]
Here is a rebase of Palak's v2 patch. I didn't change anything except
for the required resource manager API change, a pgindent run, and
removal of a stray file, and there is still some feedback to be
addressed before we can get this in, but I wanted to fix the bitrot
and re-open this CF item because this is very useful work. It's
essential for testing the prefetching-related stuff happening in
various other threads, where you want to be able to get the buffer
pool into various interesting states.
From 911776e07a767e8775f9e43948f4145f72d1de65 Mon Sep 17 00:00:00 2001
From: Palak <palakchaturvedi2...@gmail.com>
Date: Fri, 30 Jun 2023 08:21:06 +0000
Subject: [PATCH v3] Invalidate Buffer By Bufnum
---
contrib/pg_buffercache/Makefile | 2 +-
contrib/pg_buffercache/meson.build | 1 +
.../pg_buffercache--1.4--1.5.sql | 6 ++
contrib/pg_buffercache/pg_buffercache.control | 2 +-
contrib/pg_buffercache/pg_buffercache_pages.c | 35 +++++++++
src/backend/storage/buffer/bufmgr.c | 74 +++++++++++++++++++
src/include/storage/bufmgr.h | 2 +
7 files changed, 120 insertions(+), 2 deletions(-)
create mode 100644 contrib/pg_buffercache/pg_buffercache--1.4--1.5.sql
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..c96848c77d8
--- /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_invalidate(IN int, IN bool default true)
+RETURNS bool
+AS 'MODULE_PATHNAME', 'pg_buffercache_invalidate'
+LANGUAGE C PARALLEL SAFE;
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..485cd988dd4 100644
--- a/contrib/pg_buffercache/pg_buffercache_pages.c
+++ b/contrib/pg_buffercache/pg_buffercache_pages.c
@@ -64,6 +64,41 @@ 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_invalidate);
+Datum
+pg_buffercache_invalidate(PG_FUNCTION_ARGS)
+{
+ Buffer bufnum;
+ bool result;
+ bool force;
+
+ if (PG_ARGISNULL(0))
+ {
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("buffernum cannot be NULL")));
+ }
+
+ bufnum = PG_GETARG_INT32(0);
+ if (bufnum <= 0 || bufnum > NBuffers)
+ {
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("buffernum is not valid")));
+
+ }
+
+ /*
+ * Check whether to force invalidate the dirty buffer. The default value
+ * of force is true.
+ */
+
+ force = PG_GETARG_BOOL(1);
+
+ result = TryInvalidateBuffer(bufnum, force);
+ PG_RETURN_BOOL(result);
+}
+
Datum
pg_buffercache_pages(PG_FUNCTION_ARGS)
{
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index bdf89bbc4dc..1d0f185edbc 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -5705,3 +5705,77 @@ ResOwnerPrintBufferPin(Datum res)
{
return DebugPrintBufferRefcount(DatumGetInt32(res));
}
+
+/*
+ * Try Invalidating a buffer using bufnum.
+ * If the buffer is invalid, the function returns false.
+ * The function checks for dirty buffer and flushes the dirty buffer before invalidating.
+ * If the buffer is still dirty it returns false.
+ */
+bool
+TryInvalidateBuffer(Buffer bufnum, bool force)
+{
+ BufferDesc *bufHdr = GetBufferDescriptor(bufnum - 1);
+ uint32 buf_state;
+
+ ReservePrivateRefCountEntry();
+
+ buf_state = LockBufHdr(bufHdr);
+ if ((buf_state & BM_VALID) == BM_VALID)
+ {
+ /*
+ * The buffer is pinned therefore cannot invalidate.
+ */
+ if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
+ {
+ UnlockBufHdr(bufHdr, buf_state);
+ return false;
+ }
+ if ((buf_state & BM_DIRTY) == BM_DIRTY)
+ {
+ /*
+ * If the buffer is dirty and the user has not asked to clear the
+ * dirty buffer return false. Otherwise clear the dirty buffer.
+ */
+ if (!force)
+ {
+ return false;
+ }
+
+ /*
+ * Try once to flush the dirty buffer.
+ */
+ ResourceOwnerEnlarge(CurrentResourceOwner);
+ PinBuffer_Locked(bufHdr);
+ LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
+ FlushBuffer(bufHdr, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
+ LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
+ UnpinBuffer(bufHdr);
+ buf_state = LockBufHdr(bufHdr);
+ if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
+ {
+ UnlockBufHdr(bufHdr, buf_state);
+ return false;
+ }
+
+ /*
+ * If its dirty again or not valid anymore give up.
+ */
+
+ if ((buf_state & (BM_DIRTY | BM_VALID)) != (BM_VALID))
+ {
+ UnlockBufHdr(bufHdr, buf_state);
+ return false;
+ }
+
+ }
+
+ InvalidateBuffer(bufHdr);
+ return true;
+ }
+ else
+ {
+ UnlockBufHdr(bufHdr, buf_state);
+ return false;
+ }
+}
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index d51d46d3353..a7d2dd2de0a 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -250,6 +250,8 @@ extern bool HoldingBufferPinThatDelaysRecovery(void);
extern bool BgBufferSync(struct WritebackContext *wb_context);
+extern bool TryInvalidateBuffer(Buffer bufnum, bool force);
+
/* in buf_init.c */
extern void InitBufferPool(void);
extern Size BufferShmemSize(void);
--
2.39.2
