From f57791985ac3d776cb67e9d69befde538cfdf13b Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Fri, 22 Aug 2014 00:28:37 +0200
Subject: [PATCH] Add pinning_backends column to the pg_buffercache extension.
The new column shows how many backends have a buffer pinned. That can
be useful during development or to diagnose production issues
e.g. caused by vacuum waiting for cleanup locks.
To handle upgrades transparently - the extension might be used in
views - deal with callers expecting the old number of columns.
Reviewed by Fujii Masao and Rajeev rastogi.
---
contrib/pg_buffercache/Makefile | 2 +-
.../pg_buffercache--1.0--1.1.sql | 11 ++++++
...cache--1.0.sql => pg_buffercache--1.1.sql} | 5 ++-
contrib/pg_buffercache/pg_buffercache.control | 2 +-
contrib/pg_buffercache/pg_buffercache_pages.c | 37 ++++++++++++++++++-
doc/src/sgml/pgbuffercache.sgml | 7 ++++
6 files changed, 58 insertions(+), 6 deletions(-)
create mode 100644 contrib/pg_buffercache/pg_buffercache--1.0--1.1.sql
rename contrib/pg_buffercache/{pg_buffercache--1.0.sql => pg_buffercache--1.1.sql} (88%)
diff --git a/contrib/pg_buffercache/Makefile b/contrib/pg_buffercache/Makefile
index c5297d98d48..065d3d690a9 100644
--- a/contrib/pg_buffercache/Makefile
+++ b/contrib/pg_buffercache/Makefile
@@ -4,7 +4,7 @@ MODULE_big = pg_buffercache
OBJS = pg_buffercache_pages.o $(WIN32RES)
EXTENSION = pg_buffercache
-DATA = pg_buffercache--1.0.sql pg_buffercache--unpackaged--1.0.sql
+DATA = pg_buffercache--1.1.sql pg_buffercache--1.0--1.1.sql pg_buffercache--unpackaged--1.0.sql
PGFILEDESC = "pg_buffercache - monitoring of shared buffer cache in real-time"
ifdef USE_PGXS
diff --git a/contrib/pg_buffercache/pg_buffercache--1.0--1.1.sql b/contrib/pg_buffercache/pg_buffercache--1.0--1.1.sql
new file mode 100644
index 00000000000..54d02f58c01
--- /dev/null
+++ b/contrib/pg_buffercache/pg_buffercache--1.0--1.1.sql
@@ -0,0 +1,11 @@
+/* contrib/pg_buffercache/pg_buffercache--1.0--1.1.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_buffercache UPDATE TO '1.1'" to load this file. \quit
+
+-- Upgrade view to 1.1. format
+CREATE OR REPLACE VIEW pg_buffercache AS
+ SELECT P.* FROM pg_buffercache_pages() AS P
+ (bufferid integer, relfilenode oid, reltablespace oid, reldatabase oid,
+ relforknumber int2, relblocknumber int8, isdirty bool, usagecount int2,
+ pinning_backends int4);
diff --git a/contrib/pg_buffercache/pg_buffercache--1.0.sql b/contrib/pg_buffercache/pg_buffercache--1.1.sql
similarity index 88%
rename from contrib/pg_buffercache/pg_buffercache--1.0.sql
rename to contrib/pg_buffercache/pg_buffercache--1.1.sql
index 4ca4c44256c..f3b6482fa62 100644
--- a/contrib/pg_buffercache/pg_buffercache--1.0.sql
+++ b/contrib/pg_buffercache/pg_buffercache--1.1.sql
@@ -1,4 +1,4 @@
-/* contrib/pg_buffercache/pg_buffercache--1.0.sql */
+/* contrib/pg_buffercache/pg_buffercache--1.1.sql */
-- complain if script is sourced in psql, rather than via CREATE EXTENSION
\echo Use "CREATE EXTENSION pg_buffercache" to load this file. \quit
@@ -13,7 +13,8 @@ LANGUAGE C;
CREATE VIEW pg_buffercache AS
SELECT P.* FROM pg_buffercache_pages() AS P
(bufferid integer, relfilenode oid, reltablespace oid, reldatabase oid,
- relforknumber int2, relblocknumber int8, isdirty bool, usagecount int2);
+ relforknumber int2, relblocknumber int8, isdirty bool, usagecount int2,
+ pinning_backends int4);
-- Don't want these to be available to public.
REVOKE ALL ON FUNCTION pg_buffercache_pages() FROM PUBLIC;
diff --git a/contrib/pg_buffercache/pg_buffercache.control b/contrib/pg_buffercache/pg_buffercache.control
index 709513c334e..5494e2fae52 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 = '1.0'
+default_version = '1.1'
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 b205683bffc..d3b1ba3245d 100644
--- a/contrib/pg_buffercache/pg_buffercache_pages.c
+++ b/contrib/pg_buffercache/pg_buffercache_pages.c
@@ -15,7 +15,8 @@
#include "storage/bufmgr.h"
-#define NUM_BUFFERCACHE_PAGES_ELEM 8
+#define NUM_BUFFERCACHE_PAGES_MIN_ELEM 8
+#define NUM_BUFFERCACHE_PAGES_ELEM 9
PG_MODULE_MAGIC;
@@ -33,6 +34,12 @@ typedef struct
bool isvalid;
bool isdirty;
uint16 usagecount;
+ /*
+ * An int32 is sufficiently large, as MAX_BACKENDS prevents a buffer from
+ * being pinned by too many backends and each backend will only pin once
+ * because of bufmgr.c's PrivateRefCount array.
+ */
+ int32 pinning_backends;
} BufferCachePagesRec;
@@ -60,6 +67,7 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
MemoryContext oldcontext;
BufferCachePagesContext *fctx; /* User function context. */
TupleDesc tupledesc;
+ TupleDesc expected_tupledesc;
HeapTuple tuple;
if (SRF_IS_FIRSTCALL())
@@ -75,8 +83,23 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
/* Create a user function context for cross-call persistence */
fctx = (BufferCachePagesContext *) palloc(sizeof(BufferCachePagesContext));
+ /*
+ * To smoothly support upgrades from version 1.0 of this extension
+ * transparently handle the (non-)existance of the pinning_backends
+ * column. We unfortunately have to get the result type for that... -
+ * we can't use the result type determined by the function definition
+ * without potentially crashing when somebody uses the old (or even
+ * wrong) function definition though.
+ */
+ if (get_call_result_type(fcinfo, NULL, &expected_tupledesc) != TYPEFUNC_COMPOSITE)
+ elog(ERROR, "return type must be a row type");
+
+ if (expected_tupledesc->natts < NUM_BUFFERCACHE_PAGES_MIN_ELEM ||
+ expected_tupledesc->natts > NUM_BUFFERCACHE_PAGES_ELEM)
+ elog(ERROR, "incorrect number of output arguments");
+
/* Construct a tuple descriptor for the result rows. */
- tupledesc = CreateTemplateTupleDesc(NUM_BUFFERCACHE_PAGES_ELEM, false);
+ tupledesc = CreateTemplateTupleDesc(expected_tupledesc->natts, false);
TupleDescInitEntry(tupledesc, (AttrNumber) 1, "bufferid",
INT4OID, -1, 0);
TupleDescInitEntry(tupledesc, (AttrNumber) 2, "relfilenode",
@@ -94,6 +117,10 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
TupleDescInitEntry(tupledesc, (AttrNumber) 8, "usage_count",
INT2OID, -1, 0);
+ if (expected_tupledesc->natts == NUM_BUFFERCACHE_PAGES_ELEM)
+ TupleDescInitEntry(tupledesc, (AttrNumber) 9, "pinning_backends",
+ INT4OID, -1, 0);
+
fctx->tupdesc = BlessTupleDesc(tupledesc);
/* Allocate NBuffers worth of BufferCachePagesRec records. */
@@ -131,6 +158,7 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
fctx->record[i].forknum = bufHdr->tag.forkNum;
fctx->record[i].blocknum = bufHdr->tag.blockNum;
fctx->record[i].usagecount = bufHdr->usage_count;
+ fctx->record[i].pinning_backends = bufHdr->refcount;
if (bufHdr->flags & BM_DIRTY)
fctx->record[i].isdirty = true;
@@ -185,6 +213,8 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
nulls[5] = true;
nulls[6] = true;
nulls[7] = true;
+ /* unused for v1.0 callers, but the array is always long enough */
+ nulls[8] = true;
}
else
{
@@ -202,6 +232,9 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
nulls[6] = false;
values[7] = Int16GetDatum(fctx->record[i].usagecount);
nulls[7] = false;
+ /* unused for v1.0 callers, but the array is always long enough */
+ values[8] = Int32GetDatum(fctx->record[i].pinning_backends);
+ nulls[8] = false;
}
/* Build and return the tuple. */
diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml
index 4eb02c06239..f379be225f0 100644
--- a/doc/src/sgml/pgbuffercache.sgml
+++ b/doc/src/sgml/pgbuffercache.sgml
@@ -106,6 +106,13 @@
<entry>Clock-sweep access count</entry>
</row>
+ <row>
+ <entry><structfield>pinning_backends</structfield></entry>
+ <entry><type>integer</type></entry>
+ <entry></entry>
+ <entry>Number of backends pinning this buffer</entry>
+ </row>
+
</tbody>
</tgroup>
</table>
--
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