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Cherry-pick: Add pg_buffercache_usage_counts() to contrib/pg_buffercache. (#1492)
Turns out, `CREATE EXTENSION pg_buffercache` does not work on main. It is failing due pg_buffercache_usage_counts function is missing. This function was committed to PostgreSQL as part of postgres/postgres@f3fa313 Extension sql 1.4.1 version was cherry-picked to Cloudberry as part of #883 (see commit 79f2d28) ``` CREATE EXTENSION pg_buffercache; +ERROR: function pg_buffercache_usage_counts() does not exist ``` This pr fixes cherry-pick issues, and adds this extension to `ic-contrib` check Found during PG16 rebase work Original commit msg: It was pointed out that pg_buffercache_summary()'s report of the overall average usage count isn't that useful, and what would be more helpful in many cases is to report totals for each possible usage count. Add a new function to do it like that. Since pg_buffercache 1.4 is already new for v16, we don't need to create a new extension version; we'll just define this as part of 1.4. Nathan Bossart Discussion: https://postgr.es/m/20230130233040.GA2800702@nathanxps13
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‎.github/workflows/build-cloudberry.yml‎

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@@ -298,6 +298,7 @@ jobs:
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"contrib/pgcrypto:installcheck",
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"contrib/tablefunc:installcheck",
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"contrib/passwordcheck:installcheck",
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"contrib/pg_buffercache:installcheck",
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"contrib/sslinfo:installcheck"]
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},
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{"test":"ic-gpcontrib",

‎.github/workflows/build-deb-cloudberry.yml‎

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@@ -237,6 +237,7 @@ jobs:
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"contrib/pgcrypto:installcheck",
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"contrib/tablefunc:installcheck",
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"contrib/passwordcheck:installcheck",
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"contrib/pg_buffercache:installcheck",
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"contrib/sslinfo:installcheck"]
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},
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{"test":"ic-deb-gpcontrib",

‎contrib/pg_buffercache/expected/pg_buffercache.out‎

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@@ -17,9 +17,24 @@ from pg_buffercache_summary();
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t | t | t
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(1 row)
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SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
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?column?
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----------
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t
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(1 row)
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-- Check that the functions / views can't be accessed by default. To avoid
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-- having to create a dedicated user, use the pg_database_owner pseudo-role.
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SET ROLE pg_database_owner;
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SELECT * FROM pg_buffercache;
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ERROR: permission denied for view pg_buffercache
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SELECT * FROM pg_buffercache_pages() AS p (wrong int);
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ERROR: permission denied for function pg_buffercache_pages
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SELECT * FROM pg_buffercache_summary();
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ERROR: permission denied for function pg_buffercache_summary
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SELECT * FROM pg_buffercache_usage_counts();
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ERROR: permission denied for function pg_buffercache_usage_counts
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RESET role;
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SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
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?column?
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----------
@@ -72,17 +87,7 @@ SELECT count(*) > 0 FROM gp_buffercache_usage_counts_aggregated WHERE buffers >=
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(1 row)
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-- Check that the functions / views can't be accessed by default.
75-
CREATE ROLE buffercache_test;
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SET ROLE buffercache_test;
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SELECT * FROM pg_buffercache;
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ERROR: permission denied for view pg_buffercache
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SELECT * FROM pg_buffercache_pages() AS p (wrong int);
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ERROR: permission denied for function pg_buffercache_pages
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SELECT * FROM pg_buffercache_summary();
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ERROR: permission denied for function pg_buffercache_summary
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RESET role;
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SELECT * FROM pg_buffercache_usage_counts();
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ERROR: permission denied for function pg_buffercache_usage_counts
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SET ROLE pg_database_owner;
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-- GPDB
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SELECT * FROM pg_buffercache_summary;
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ERROR: permission denied for view pg_buffercache_summary
@@ -166,4 +171,3 @@ SELECT count(*) > 0 FROM gp_buffercache_usage_counts_aggregated;
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(1 row)
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RESET ROLE;
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DROP ROLE buffercache_test;

‎contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql‎

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Original file line numberDiff line numberDiff line change
@@ -12,6 +12,17 @@ CREATE FUNCTION pg_buffercache_summary(
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AS 'MODULE_PATHNAME', 'pg_buffercache_summary'
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LANGUAGE C PARALLEL SAFE;
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CREATE FUNCTION pg_buffercache_usage_counts(
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OUT usage_count int4,
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OUT buffers int4,
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OUT dirty int4,
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OUT pinned int4)
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RETURNS SETOF record
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AS 'MODULE_PATHNAME', 'pg_buffercache_usage_counts'
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LANGUAGE C PARALLEL SAFE;
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-- Don't want these to be available to public.
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REVOKE ALL ON FUNCTION pg_buffercache_summary() FROM PUBLIC;
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GRANT EXECUTE ON FUNCTION pg_buffercache_summary() TO pg_monitor;
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REVOKE ALL ON FUNCTION pg_buffercache_usage_counts() FROM PUBLIC;
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GRANT EXECUTE ON FUNCTION pg_buffercache_usage_counts() TO pg_monitor;

‎contrib/pg_buffercache/pg_buffercache_pages.c‎

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Original file line numberDiff line numberDiff line change
@@ -18,6 +18,7 @@
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#define NUM_BUFFERCACHE_PAGES_MIN_ELEM 8
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#define NUM_BUFFERCACHE_PAGES_ELEM 9
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#define NUM_BUFFERCACHE_SUMMARY_ELEM 5
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#define NUM_BUFFERCACHE_USAGE_COUNTS_ELEM 4
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PG_MODULE_MAGIC;
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@@ -61,6 +62,7 @@ typedef struct
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*/
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PG_FUNCTION_INFO_V1(pg_buffercache_pages);
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PG_FUNCTION_INFO_V1(pg_buffercache_summary);
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PG_FUNCTION_INFO_V1(pg_buffercache_usage_counts);
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Datum
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pg_buffercache_pages(PG_FUNCTION_ARGS)
@@ -304,3 +306,44 @@ pg_buffercache_summary(PG_FUNCTION_ARGS)
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PG_RETURN_DATUM(result);
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}
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Datum
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pg_buffercache_usage_counts(PG_FUNCTION_ARGS)
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{
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ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
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int usage_counts[BM_MAX_USAGE_COUNT + 1] = {0};
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int dirty[BM_MAX_USAGE_COUNT + 1] = {0};
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int pinned[BM_MAX_USAGE_COUNT + 1] = {0};
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Datum values[NUM_BUFFERCACHE_USAGE_COUNTS_ELEM];
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bool nulls[NUM_BUFFERCACHE_USAGE_COUNTS_ELEM] = {0};
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InitMaterializedSRF(fcinfo, 0);
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for (int i = 0; i < NBuffers; i++)
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{
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BufferDesc *bufHdr = GetBufferDescriptor(i);
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uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
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int usage_count;
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usage_count = BUF_STATE_GET_USAGECOUNT(buf_state);
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usage_counts[usage_count]++;
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if (buf_state & BM_DIRTY)
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dirty[usage_count]++;
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if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
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pinned[usage_count]++;
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}
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for (int i = 0; i < BM_MAX_USAGE_COUNT + 1; i++)
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{
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values[0] = Int32GetDatum(i);
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values[1] = Int32GetDatum(usage_counts[i]);
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values[2] = Int32GetDatum(dirty[i]);
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values[3] = Int32GetDatum(pinned[i]);
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tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
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}
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return (Datum) 0;
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}

‎contrib/pg_buffercache/sql/pg_buffercache.sql‎

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@@ -10,12 +10,15 @@ select buffers_used + buffers_unused > 0,
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buffers_pinned <= buffers_used
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from pg_buffercache_summary();
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SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
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-- Check that the functions / views can't be accessed by default. To avoid
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-- having to create a dedicated user, use the pg_database_owner pseudo-role.
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SET ROLE pg_database_owner;
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SELECT * FROM pg_buffercache;
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SELECT * FROM pg_buffercache_pages() AS p (wrong int);
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SELECT * FROM pg_buffercache_summary();
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SELECT * FROM pg_buffercache_usage_counts();
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RESET role;
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SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
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@@ -42,12 +45,7 @@ SELECT count(*) > 0 FROM gp_buffercache_usage_counts WHERE buffers >= 0;
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SELECT count(*) > 0 FROM gp_buffercache_usage_counts_aggregated WHERE buffers >= 0;
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-- Check that the functions / views can't be accessed by default.
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CREATE ROLE buffercache_test;
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SET ROLE buffercache_test;
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SELECT * FROM pg_buffercache;
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SELECT * FROM pg_buffercache_pages() AS p (wrong int);
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SELECT * FROM pg_buffercache_summary();
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SELECT * FROM pg_buffercache_usage_counts();
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SET ROLE pg_database_owner;
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-- GPDB
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SELECT * FROM pg_buffercache_summary;
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SELECT * FROM pg_buffercache_usage_counts;
@@ -73,5 +71,3 @@ SELECT buffers_used + buffers_unused > 0 FROM gp_buffercache_summary_aggregated;
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SELECT count(*) > 0 FROM gp_buffercache_usage_counts;
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SELECT count(*) > 0 FROM gp_buffercache_usage_counts_aggregated;
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RESET ROLE;
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DROP ROLE buffercache_test;

‎doc/src/sgml/pgbuffercache.sgml‎

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@@ -21,9 +21,10 @@
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</indexterm>
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<para>
24-
The module provides the <function>pg_buffercache_pages()</function>
25-
function, wrapped in the <structname>pg_buffercache</structname> view, and
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the <function>pg_buffercache_summary()</function> function.
24+
This module provides the <function>pg_buffercache_pages()</function>
25+
function (wrapped in the <structname>pg_buffercache</structname> view),
26+
the <function>pg_buffercache_summary()</function> function, and the
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<function>pg_buffercache_usage_counts()</function> function.
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</para>
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<para>
@@ -38,6 +39,12 @@
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row summarizing the state of the shared buffer cache.
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</para>
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<para>
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The <function>pg_buffercache_usage_counts()</function> function returns a set
44+
of records, each row describing the number of buffers with a given usage
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count.
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</para>
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<para>
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By default, use is restricted to superusers and roles with privileges of the
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<literal>pg_monitor</literal> role. Access may be granted to others
@@ -242,7 +249,7 @@
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<structfield>usagecount_avg</structfield> <type>float8</type>
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</para>
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<para>
245-
Average usagecount of used shared buffers
252+
Average usage count of used shared buffers
246253
</para></entry>
247254
</row>
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</tbody>
@@ -266,6 +273,84 @@
266273
</sect2>
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<sect2>
276+
<title>The <function>pg_buffercache_usage_counts()</function> Function</title>
277+
278+
<para>
279+
The definitions of the columns exposed by the function are shown in
280+
<xref linkend="pgbuffercache_usage_counts-columns"/>.
281+
</para>
282+
283+
<table id="pgbuffercache_usage_counts-columns">
284+
<title><function>pg_buffercache_usage_counts()</function> Output Columns</title>
285+
<tgroup cols="1">
286+
<thead>
287+
<row>
288+
<entry role="catalog_table_entry"><para role="column_definition">
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Column Type
290+
</para>
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<para>
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Description
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</para></entry>
294+
</row>
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</thead>
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297+
<tbody>
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<row>
299+
<entry role="catalog_table_entry"><para role="column_definition">
300+
<structfield>usage_count</structfield> <type>int4</type>
301+
</para>
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<para>
303+
A possible buffer usage count
304+
</para></entry>
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</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
309+
<structfield>buffers</structfield> <type>int4</type>
310+
</para>
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<para>
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Number of buffers with the usage count
313+
</para></entry>
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</row>
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316+
<row>
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<entry role="catalog_table_entry"><para role="column_definition">
318+
<structfield>dirty</structfield> <type>int4</type>
319+
</para>
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<para>
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Number of dirty buffers with the usage count
322+
</para></entry>
323+
</row>
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<row>
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<entry role="catalog_table_entry"><para role="column_definition">
327+
<structfield>pinned</structfield> <type>int4</type>
328+
</para>
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<para>
330+
Number of pinned buffers with the usage count
331+
</para></entry>
332+
</row>
333+
</tbody>
334+
</tgroup>
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</table>
336+
337+
<para>
338+
The <function>pg_buffercache_usage_counts()</function> function returns a
339+
set of rows summarizing the states of all shared buffers, aggregated over
340+
the possible usage count values. Similar and more detailed information is
341+
provided by the <structname>pg_buffercache</structname> view, but
342+
<function>pg_buffercache_usage_counts()</function> is significantly cheaper.
343+
</para>
344+
345+
<para>
346+
Like the <structname>pg_buffercache</structname> view,
347+
<function>pg_buffercache_usage_counts()</function> does not acquire buffer
348+
manager locks. Therefore concurrent activity can lead to minor inaccuracies
349+
in the result.
350+
</para>
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</sect2>
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353+
<sect2 id="pgbuffercache-sample-output">
269354
<title>Sample Output</title>
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271356
<screen>
@@ -299,6 +384,18 @@ regression=# SELECT * FROM pg_buffercache_summary();
299384
--------------+----------------+---------------+----------------+----------------
300385
248 | 2096904 | 39 | 0 | 3.141129
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(1 row)
387+
388+
389+
regression=# SELECT * FROM pg_buffercache_usage_counts();
390+
usage_count | buffers | dirty | pinned
391+
-------------+---------+-------+--------
392+
0 | 14650 | 0 | 0
393+
1 | 1436 | 671 | 0
394+
2 | 102 | 88 | 0
395+
3 | 23 | 21 | 0
396+
4 | 9 | 7 | 0
397+
5 | 164 | 106 | 0
398+
(6 rows)
302399
</screen>
303400
</sect2>
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