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
t | t | t
(1 row)
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
+ ?column?
+----------
+ 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;
ERROR: permission denied for function pg_buffercache_pages
SELECT * FROM pg_buffercache_summary();
ERROR: permission denied for function pg_buffercache_summary
+SELECT * FROM pg_buffercache_usage_counts();
+ERROR: permission denied for function pg_buffercache_usage_counts
RESET role;
-- Check that pg_monitor is allowed to query view / function
SET ROLE pg_monitor;
t
(1 row)
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts();
+ ?column?
+----------
+ t
+(1 row)
+
AS 'MODULE_PATHNAME', 'pg_buffercache_summary'
LANGUAGE C PARALLEL SAFE;
+CREATE FUNCTION pg_buffercache_usage_counts(
+ OUT usage_count int4,
+ OUT buffers int4,
+ OUT dirty int4,
+ OUT pinned int4)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_buffercache_usage_counts'
+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;
+REVOKE ALL ON FUNCTION pg_buffercache_usage_counts() FROM PUBLIC;
+GRANT EXECUTE ON FUNCTION pg_buffercache_usage_counts() TO pg_monitor;
#define NUM_BUFFERCACHE_PAGES_MIN_ELEM 8
#define NUM_BUFFERCACHE_PAGES_ELEM 9
#define NUM_BUFFERCACHE_SUMMARY_ELEM 5
+#define NUM_BUFFERCACHE_USAGE_COUNTS_ELEM 4
PG_MODULE_MAGIC;
*/
PG_FUNCTION_INFO_V1(pg_buffercache_pages);
PG_FUNCTION_INFO_V1(pg_buffercache_summary);
+PG_FUNCTION_INFO_V1(pg_buffercache_usage_counts);
Datum
pg_buffercache_pages(PG_FUNCTION_ARGS)
PG_RETURN_DATUM(result);
}
+
+Datum
+pg_buffercache_usage_counts(PG_FUNCTION_ARGS)
+{
+ ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+ int usage_counts[BM_MAX_USAGE_COUNT + 1] = {0};
+ int dirty[BM_MAX_USAGE_COUNT + 1] = {0};
+ int pinned[BM_MAX_USAGE_COUNT + 1] = {0};
+ Datum values[NUM_BUFFERCACHE_USAGE_COUNTS_ELEM];
+ bool nulls[NUM_BUFFERCACHE_USAGE_COUNTS_ELEM] = {0};
+
+ InitMaterializedSRF(fcinfo, 0);
+
+ for (int i = 0; i < NBuffers; i++)
+ {
+ BufferDesc *bufHdr = GetBufferDescriptor(i);
+ uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
+ int usage_count;
+
+ usage_count = BUF_STATE_GET_USAGECOUNT(buf_state);
+ usage_counts[usage_count]++;
+
+ if (buf_state & BM_DIRTY)
+ dirty[usage_count]++;
+
+ if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
+ pinned[usage_count]++;
+ }
+
+ for (int i = 0; i < BM_MAX_USAGE_COUNT + 1; i++)
+ {
+ values[0] = Int32GetDatum(i);
+ values[1] = Int32GetDatum(usage_counts[i]);
+ values[2] = Int32GetDatum(dirty[i]);
+ values[3] = Int32GetDatum(pinned[i]);
+
+ tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+ }
+
+ return (Datum) 0;
+}
buffers_pinned <= buffers_used
from pg_buffercache_summary();
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
+
-- 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();
+SELECT * FROM pg_buffercache_usage_counts();
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();
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts();
- The module provides the pg_buffercache_pages()
- function, wrapped in the pg_buffercache view, and
- the pg_buffercache_summary() function.
+ This module provides the pg_buffercache_pages()
+ function (wrapped in the pg_buffercache view),
+ the pg_buffercache_summary() function, and the
+ pg_buffercache_usage_counts() function.
row summarizing the state of the shared buffer cache.
+ The pg_buffercache_usage_counts() function returns a set
+ of records, each row describing the number of buffers with a given usage
+ count.
+
+
By default, use is restricted to superusers and roles with privileges of the
pg_monitor role. Access may be granted to others
usagecount_avg float8
- Average usagecount of used shared buffers
+ Average usage count of used shared buffers
+
+
The <function>pg_buffercache_usage_counts()</function> Function
+
+ The definitions of the columns exposed by the function are shown in
+ .
+
+
+
<function>pg_buffercache_usage_counts()</function> Output Columns
+
+
+ |
+ Column Type
+
+ Description
+
+
+
+
+
+ |
+ usage_count int4
+
+ A possible buffer usage count
+
+
+
+ |
+ buffers int4
+
+ Number of buffers with the usage count
+
+
+
+ |
+ dirty int4
+
+ Number of dirty buffers with the usage count
+
+
+
+ |
+ pinned int4
+
+ Number of pinned buffers with the usage count
+
+
+
+
+
+
+ The pg_buffercache_usage_counts() function returns a
+ set of rows summarizing the states of all shared buffers, aggregated over
+ the possible usage count values. Similar and more detailed information is
+ provided by the pg_buffercache view, but
+ pg_buffercache_usage_counts() is significantly cheaper.
+
+
+ Like the pg_buffercache view,
+ pg_buffercache_usage_counts() does not acquire buffer
+ manager locks. Therefore concurrent activity can lead to minor inaccuracies
+ in the result.
+
+
+
Sample Output
--------------+----------------+---------------+----------------+----------------
248 | 2096904 | 39 | 0 | 3.141129
(1 row)
+
+
+regression=# SELECT * FROM pg_buffercache_usage_counts();
+ usage_count | buffers | dirty | pinned
+-------------+---------+-------+--------
+ 0 | 14650 | 0 | 0
+ 1 | 1436 | 671 | 0
+ 2 | 102 | 88 | 0
+ 3 | 23 | 21 | 0
+ 4 | 9 | 7 | 0
+ 5 | 164 | 106 | 0
+(6 rows)
projects / postgresql.git / commitdiff