diff --git a/contrib/pg_buffercache/Makefile b/contrib/pg_buffercache/Makefile index d74b3e853c6..d6b58d4da94 100644 --- a/contrib/pg_buffercache/Makefile +++ b/contrib/pg_buffercache/Makefile @@ -7,7 +7,8 @@ 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--1.1--1.2.sql pg_buffercache--1.0--1.1.sql \ + pg_buffercache--1.3--1.4.sql PGFILEDESC = "pg_buffercache - monitoring of shared buffer cache in real-time" REGRESS = pg_buffercache diff --git a/contrib/pg_buffercache/expected/pg_buffercache.out b/contrib/pg_buffercache/expected/pg_buffercache.out index 138556efc9f..635f01e3b21 100644 --- a/contrib/pg_buffercache/expected/pg_buffercache.out +++ b/contrib/pg_buffercache/expected/pg_buffercache.out @@ -8,3 +8,36 @@ from pg_buffercache; t (1 row) +select buffers_used + buffers_unused > 0, + buffers_dirty <= buffers_used, + buffers_pinned <= buffers_used +from pg_buffercache_summary(); + ?column? | ?column? | ?column? +----------+----------+---------- + 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/meson.build b/contrib/pg_buffercache/meson.build index dd9948e5f0b..ff7f9162cee 100644 --- a/contrib/pg_buffercache/meson.build +++ b/contrib/pg_buffercache/meson.build @@ -19,6 +19,7 @@ install_data( 'pg_buffercache--1.1--1.2.sql', 'pg_buffercache--1.2--1.3.sql', 'pg_buffercache--1.2.sql', + 'pg_buffercache--1.3--1.4.sql', 'pg_buffercache.control', kwargs: contrib_data_args, ) diff --git a/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql b/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql new file mode 100644 index 00000000000..8f212dc5e93 --- /dev/null +++ b/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql @@ -0,0 +1,17 @@ +/* contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql */ + +-- 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( + 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.control b/contrib/pg_buffercache/pg_buffercache.control index 8c060ae9abf..a82ae5f9bb5 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 = '1.3' +default_version = '1.4' 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 c5754ea9fa5..1c6a2f22caa 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -17,6 +17,7 @@ #define NUM_BUFFERCACHE_PAGES_MIN_ELEM 8 #define NUM_BUFFERCACHE_PAGES_ELEM 9 +#define NUM_BUFFERCACHE_SUMMARY_ELEM 5 PG_MODULE_MAGIC; @@ -59,6 +60,7 @@ typedef struct * relation node/tablespace/database/blocknum and dirty indicator. */ PG_FUNCTION_INFO_V1(pg_buffercache_pages); +PG_FUNCTION_INFO_V1(pg_buffercache_summary); Datum pg_buffercache_pages(PG_FUNCTION_ARGS) @@ -237,3 +239,68 @@ pg_buffercache_pages(PG_FUNCTION_ARGS) else SRF_RETURN_DONE(funcctx); } + +Datum +pg_buffercache_summary(PG_FUNCTION_ARGS) +{ + Datum result; + TupleDesc tupledesc; + HeapTuple tuple; + Datum values[NUM_BUFFERCACHE_SUMMARY_ELEM]; + bool nulls[NUM_BUFFERCACHE_SUMMARY_ELEM]; + + int32 buffers_used = 0; + int32 buffers_unused = 0; + int32 buffers_dirty = 0; + int32 buffers_pinned = 0; + int64 usagecount_total = 0; + + 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++) + { + BufferDesc *bufHdr; + uint32 buf_state; + + /* + * This function summarizes the state of all headers. Locking the + * buffer headers wouldn't provide an improved result as the state of + * the buffer can still change after we release the lock and it'd + * noticeably increase the cost of the function. + */ + bufHdr = GetBufferDescriptor(i); + buf_state = pg_atomic_read_u32(&bufHdr->state); + + if (buf_state & BM_VALID) + { + buffers_used++; + usagecount_total += BUF_STATE_GET_USAGECOUNT(buf_state); + + if (buf_state & BM_DIRTY) + buffers_dirty++; + } + else + buffers_unused++; + + if (BUF_STATE_GET_REFCOUNT(buf_state) > 0) + buffers_pinned++; + } + + memset(nulls, 0, sizeof(nulls)); + values[0] = Int32GetDatum(buffers_used); + values[1] = Int32GetDatum(buffers_unused); + values[2] = Int32GetDatum(buffers_dirty); + values[3] = Int32GetDatum(buffers_pinned); + + if (buffers_used != 0) + values[4] = Float8GetDatum((double) usagecount_total / buffers_used); + else + nulls[4] = true; + + /* Build and return the tuple. */ + tuple = heap_form_tuple(tupledesc, values, nulls); + result = HeapTupleGetDatum(tuple); + + PG_RETURN_DATUM(result); +} diff --git a/contrib/pg_buffercache/sql/pg_buffercache.sql b/contrib/pg_buffercache/sql/pg_buffercache.sql index e1ba6f7e8d4..2e2e0a74517 100644 --- a/contrib/pg_buffercache/sql/pg_buffercache.sql +++ b/contrib/pg_buffercache/sql/pg_buffercache.sql @@ -4,3 +4,21 @@ select count(*) = (select setting::bigint from pg_settings where name = 'shared_buffers') from pg_buffercache; + +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 a06fd3e26de..8f314ee8ff4 100644 --- a/doc/src/sgml/pgbuffercache.sgml +++ b/doc/src/sgml/pgbuffercache.sgml @@ -16,13 +16,28 @@ pg_buffercache_pages + + pg_buffercache_summary + + - The module provides a C function pg_buffercache_pages - that returns a set of records, plus a view - pg_buffercache that wraps the function for + 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, 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 single + row summarizing the state of the shared buffer cache. + + By default, use is restricted to superusers and roles with privileges of the pg_monitor role. Access may be granted to others @@ -164,6 +179,92 @@ + + The <function>pg_buffercache_summary()</function> Function + + + The definitions of the columns exposed by the function are shown in . + + + + <function>pg_buffercache_summary()</function> Output Columns + + + + + Column Type + + + Description + + + + + + + + buffers_used int4 + + + Number of unused shared buffers + + + + + + buffers_unused int4 + + + Number of unused shared buffers + + + + + + buffers_dirty int4 + + + Number of dirty shared buffers + + + + + + buffers_pinned int4 + + + Number of pinned shared buffers + + + + + + usagecount_avg float8 + + + Average usagecount of used shared buffers + + + + +
+ + + 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. + + + + 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. + + + Sample Output @@ -191,6 +292,13 @@ regression=# SELECT n.nspname, c.relname, count(*) AS buffers public | gin_test_tbl | 188 public | spgist_text_tbl | 182 (10 rows) + + +regression=# SELECT * FROM pg_buffercache_summary(); + buffers_used | buffers_unused | buffers_dirty | buffers_pinned | usagecount_avg +--------------+----------------+---------------+----------------+---------------- + 248 | 2096904 | 39 | 0 | 3.141129 +(1 row)