From 40597bd30c6c9c4ef9a87864d4f6e2b2b0d7548f Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Wed, 12 Oct 2022 12:20:43 -0700 Subject: [PATCH v15 2/2] fixup! pg_buffercache: Add pg_buffercache_summary() --- .../expected/pg_buffercache.out | 24 ++++++++ .../pg_buffercache--1.3--1.4.sql | 10 +++- contrib/pg_buffercache/pg_buffercache_pages.c | 27 ++------- contrib/pg_buffercache/sql/pg_buffercache.sql | 13 +++++ doc/src/sgml/pgbuffercache.sgml | 55 +++++++++++-------- 5 files changed, 80 insertions(+), 49 deletions(-) diff --git a/contrib/pg_buffercache/expected/pg_buffercache.out b/contrib/pg_buffercache/expected/pg_buffercache.out index 6798eb74322..635f01e3b21 100644 --- a/contrib/pg_buffercache/expected/pg_buffercache.out +++ b/contrib/pg_buffercache/expected/pg_buffercache.out @@ -17,3 +17,27 @@ from pg_buffercache_summary(); t | t | t (1 row) +-- Check that the functions / views can't be accessed by default. To avoid +-- having to create a dedicated user, use the pg_database_owner pseudo-role. +SET ROLE pg_database_owner; +SELECT * FROM pg_buffercache; +ERROR: permission denied for view pg_buffercache +SELECT * FROM pg_buffercache_pages() AS p (wrong int); +ERROR: permission denied for function pg_buffercache_pages +SELECT * FROM pg_buffercache_summary(); +ERROR: permission denied for function pg_buffercache_summary +RESET role; +-- Check that pg_monitor is allowed to query view / function +SET ROLE pg_monitor; +SELECT count(*) > 0 FROM pg_buffercache; + ?column? +---------- + t +(1 row) + +SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary(); + ?column? +---------- + t +(1 row) + diff --git a/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql b/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql index 77e250b430f..8f212dc5e93 100644 --- a/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql +++ b/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql @@ -3,11 +3,15 @@ -- complain if script is sourced in psql, rather than via ALTER EXTENSION \echo Use "ALTER EXTENSION pg_buffercache UPDATE TO '1.4'" to load this file. \quit -CREATE FUNCTION pg_buffercache_summary() -RETURNS TABLE (buffers_used int4, buffers_unused int4, buffers_dirty int4, - buffers_pinned int4, usagecount_avg real) +CREATE FUNCTION pg_buffercache_summary( + OUT buffers_used int4, + OUT buffers_unused int4, + OUT buffers_dirty int4, + OUT buffers_pinned int4, + OUT usagecount_avg float8) AS 'MODULE_PATHNAME', 'pg_buffercache_summary' LANGUAGE C PARALLEL SAFE; -- Don't want these to be available to public. REVOKE ALL ON FUNCTION pg_buffercache_summary() FROM PUBLIC; +GRANT EXECUTE ON FUNCTION pg_buffercache_summary() TO pg_monitor; diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c index a8f9750ac42..1c6a2f22caa 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -253,22 +253,10 @@ pg_buffercache_summary(PG_FUNCTION_ARGS) int32 buffers_unused = 0; int32 buffers_dirty = 0; int32 buffers_pinned = 0; - float usagecount_avg = 0; + int64 usagecount_total = 0; - /* Construct a tuple descriptor for the result rows. */ - tupledesc = CreateTemplateTupleDesc(NUM_BUFFERCACHE_SUMMARY_ELEM); - TupleDescInitEntry(tupledesc, (AttrNumber) 1, "buffers_used", - INT4OID, -1, 0); - TupleDescInitEntry(tupledesc, (AttrNumber) 2, "buffers_unused", - INT4OID, -1, 0); - TupleDescInitEntry(tupledesc, (AttrNumber) 3, "buffers_dirty", - INT4OID, -1, 0); - TupleDescInitEntry(tupledesc, (AttrNumber) 4, "buffers_pinned", - INT4OID, -1, 0); - TupleDescInitEntry(tupledesc, (AttrNumber) 5, "usagecount_avg", - FLOAT4OID, -1, 0); - - BlessTupleDesc(tupledesc); + if (get_call_result_type(fcinfo, NULL, &tupledesc) != TYPEFUNC_COMPOSITE) + elog(ERROR, "return type must be a row type"); for (int i = 0; i < NBuffers; i++) { @@ -287,7 +275,7 @@ pg_buffercache_summary(PG_FUNCTION_ARGS) if (buf_state & BM_VALID) { buffers_used++; - usagecount_avg += BUF_STATE_GET_USAGECOUNT(buf_state); + usagecount_total += BUF_STATE_GET_USAGECOUNT(buf_state); if (buf_state & BM_DIRTY) buffers_dirty++; @@ -306,14 +294,9 @@ pg_buffercache_summary(PG_FUNCTION_ARGS) values[3] = Int32GetDatum(buffers_pinned); if (buffers_used != 0) - { - usagecount_avg = usagecount_avg / buffers_used; - values[4] = Float4GetDatum(usagecount_avg); - } + values[4] = Float8GetDatum((double) usagecount_total / buffers_used); else - { nulls[4] = true; - } /* Build and return the tuple. */ tuple = heap_form_tuple(tupledesc, values, nulls); diff --git a/contrib/pg_buffercache/sql/pg_buffercache.sql b/contrib/pg_buffercache/sql/pg_buffercache.sql index 897dfbc9245..2e2e0a74517 100644 --- a/contrib/pg_buffercache/sql/pg_buffercache.sql +++ b/contrib/pg_buffercache/sql/pg_buffercache.sql @@ -9,3 +9,16 @@ select buffers_used + buffers_unused > 0, buffers_dirty <= buffers_used, buffers_pinned <= buffers_used from pg_buffercache_summary(); + +-- Check that the functions / views can't be accessed by default. To avoid +-- having to create a dedicated user, use the pg_database_owner pseudo-role. +SET ROLE pg_database_owner; +SELECT * FROM pg_buffercache; +SELECT * FROM pg_buffercache_pages() AS p (wrong int); +SELECT * FROM pg_buffercache_summary(); +RESET role; + +-- Check that pg_monitor is allowed to query view / function +SET ROLE pg_monitor; +SELECT count(*) > 0 FROM pg_buffercache; +SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary(); diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml index 6c38ee5d5eb..8f314ee8ff4 100644 --- a/doc/src/sgml/pgbuffercache.sgml +++ b/doc/src/sgml/pgbuffercache.sgml @@ -9,27 +9,33 @@ The pg_buffercache module provides a means for - examining what's happening in the shared buffer in real time. + examining what's happening in the shared buffer cache in real time. pg_buffercache_pages + + pg_buffercache_summary + + - The module provides C functions pg_buffercache_pages - and pg_buffercache_summary. + The module provides the pg_buffercache_pages() + function, wrapped in the pg_buffercache view, and + the pg_buffercache_summary() function. - The pg_buffercache_pages function - returns a set of records, plus a view pg_buffercache that wraps the function for - convenient use is provided. + The pg_buffercache_pages() function returns a set of + records, each row describing the state of one shared buffer entry. The + pg_buffercache view wraps the function for + convenient use. - The pg_buffercache_summary function returns a table with a single row - that contains summarized and aggregated information about shared buffer. + The pg_buffercache_summary() function returns a single + row summarizing the state of the shared buffer cache. @@ -174,14 +180,14 @@ - The <structname>pg_buffercache_summary</structname> Function + The <function>pg_buffercache_summary()</function> Function - The definitions of the columns exposed by the function are shown in . + The definitions of the columns exposed by the function are shown in . - - <structname>pg_buffercachesummary</structname> Columns +
+ <function>pg_buffercache_summary()</function> Output Columns @@ -200,7 +206,7 @@ buffers_used int4 - Number of shared buffers currently being used + Number of unused shared buffers @@ -209,7 +215,7 @@ buffers_unusedint4 - Number of shared buffers that not currently being used + Number of unused shared buffers @@ -227,13 +233,13 @@ buffers_pinnedint4 - Number of shared buffers that has a pinned backend + Number of pinned shared buffers - usagecount_avg float + usagecount_avg float8 Average usagecount of used shared buffers @@ -244,17 +250,18 @@
- There is a single row to show summarized information of all shared buffers. - pg_buffercache_summary is not interested - in the state of each shared buffer, only shows aggregated information. + The pg_buffercache_summary() function returns a + single row summarizing the state of all shared buffers. Similar and more + detailed information is provided by the + pg_buffercache view, but + pg_buffercache_summary() is significantly cheaper. - The pg_buffercache_summary doesn't provide a result - that is consistent across all buffers. This is intentional. The purpose - of this function is to provide a general idea about the state of shared - buffers as fast as possible. Additionally, pg_buffercache_summary - allocates much less memory. + Like the pg_buffercache view, + pg_buffercache_summary() does not acquire buffer + manager locks. Therefore concurrent activity can lead to minor inaccuracies + in the result. -- 2.38.0