From 2c93894c3f7924161ad5c0c1284f26d9a2620bed Mon Sep 17 00:00:00 2001 From: Melih Mutlu Date: Tue, 9 Aug 2022 16:42:23 +0300 Subject: [PATCH v3] Added pg_buffercache_summary function Adds pg_buffercache_summary() function into pg_buffercache extension for retrieving summary information about overall shared_buffer usage. Author: Melih Mutlu Reviewed-by: Aleksander Alekseev Discussion: https://postgr.es/m/CAGPVpCQAXYo54Q%3D8gqBsS%3Du0uk9qhnnq4%2B710BtUhUisX1XGEg%40mail.gmail.com --- contrib/pg_buffercache/Makefile | 3 +- .../expected/pg_buffercache.out | 9 ++ .../pg_buffercache--1.3--1.4.sql | 13 +++ contrib/pg_buffercache/pg_buffercache.control | 2 +- contrib/pg_buffercache/pg_buffercache_pages.c | 79 ++++++++++++- contrib/pg_buffercache/sql/pg_buffercache.sql | 5 + doc/src/sgml/pgbuffercache.sgml | 110 +++++++++++++++++- 7 files changed, 213 insertions(+), 8 deletions(-) create mode 100644 contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql diff --git a/contrib/pg_buffercache/Makefile b/contrib/pg_buffercache/Makefile index d74b3e853c..d6b58d4da9 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 138556efc9..6994761d0a 100644 --- a/contrib/pg_buffercache/expected/pg_buffercache.out +++ b/contrib/pg_buffercache/expected/pg_buffercache.out @@ -8,3 +8,12 @@ from pg_buffercache; t (1 row) +select used_buffers + unused_buffers > 0, + dirty_buffers < used_buffers, + pinned_buffers < used_buffers +from pg_buffercache_summary(); + ?column? | ?column? | ?column? +----------+----------+---------- + t | t | 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 new file mode 100644 index 0000000000..02800dbf18 --- /dev/null +++ b/contrib/pg_buffercache/pg_buffercache--1.3--1.4.sql @@ -0,0 +1,13 @@ +/* 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() +RETURNS TABLE (used_buffers int4, unused_buffers int4, dirty_buffers int4, + pinned_buffers int4, avg_usagecount real) +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; diff --git a/contrib/pg_buffercache/pg_buffercache.control b/contrib/pg_buffercache/pg_buffercache.control index 8c060ae9ab..a82ae5f9bb 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 c5754ea9fa..867f148598 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; @@ -43,7 +44,6 @@ typedef struct int32 pinning_backends; } BufferCachePagesRec; - /* * Function context for data persisting over repeated calls. */ @@ -53,12 +53,12 @@ typedef struct BufferCachePagesRec *record; } BufferCachePagesContext; - /* * Function returning data from the shared buffer cache - buffer number, * 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 +237,78 @@ 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 used_buffers = 0; + int32 unused_buffers = 0; + int32 dirty_buffers = 0; + int32 pinned_buffers = 0; + float avg_usagecount = 0; + + /* Construct a tuple descriptor for the result rows. */ + tupledesc = CreateTemplateTupleDesc(NUM_BUFFERCACHE_SUMMARY_ELEM); + TupleDescInitEntry(tupledesc, (AttrNumber) 1, "used_buffers", + INT4OID, -1, 0); + TupleDescInitEntry(tupledesc, (AttrNumber) 2, "unused_buffers", + INT4OID, -1, 0); + TupleDescInitEntry(tupledesc, (AttrNumber) 3, "dirty_buffers", + INT4OID, -1, 0); + TupleDescInitEntry(tupledesc, (AttrNumber) 4, "pinned_buffers", + INT4OID, -1, 0); + TupleDescInitEntry(tupledesc, (AttrNumber) 5, "avg_usagecount", + FLOAT4OID, -1, 0); + + BlessTupleDesc(tupledesc); + + for (int i = 0; i < NBuffers; i++) + { + BufferDesc *bufHdr; + uint32 buf_state; + + /* + * No need to get locks on buffer headers as we don't rely on the + * results in detail. Therefore, we don't get a consistent snapshot + * across all buffers and it is not guaranteed that the information of + * each buffer is self-consistent as opposed to pg_buffercache_pages. + */ + bufHdr = GetBufferDescriptor(i); + buf_state = pg_atomic_read_u32(&bufHdr->state); + + /* Invalid RelFileNumber means the buffer is unused */ + if (RelFileNumberIsValid(BufTagGetRelNumber(bufHdr))) + { + used_buffers++; + avg_usagecount += BUF_STATE_GET_USAGECOUNT(buf_state); + + if (buf_state & BM_DIRTY) + dirty_buffers++; + } + else + unused_buffers++; + + if (BUF_STATE_GET_REFCOUNT(buf_state) > 0) + pinned_buffers++; + } + avg_usagecount /= used_buffers; + + memset(nulls, 0, sizeof(nulls)); + values[0] = Int32GetDatum(used_buffers); + values[1] = Int32GetDatum(unused_buffers); + values[2] = Int32GetDatum(dirty_buffers); + values[3] = Int32GetDatum(pinned_buffers); + values[4] = Float4GetDatum(avg_usagecount); + + /* 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 e1ba6f7e8d..04e78b1faf 100644 --- a/contrib/pg_buffercache/sql/pg_buffercache.sql +++ b/contrib/pg_buffercache/sql/pg_buffercache.sql @@ -4,3 +4,8 @@ select count(*) = (select setting::bigint from pg_settings where name = 'shared_buffers') from pg_buffercache; + +select used_buffers + unused_buffers > 0, + dirty_buffers < used_buffers, + pinned_buffers < used_buffers +from pg_buffercache_summary(); \ No newline at end of file diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml index a06fd3e26d..6cf3d56c99 100644 --- a/doc/src/sgml/pgbuffercache.sgml +++ b/doc/src/sgml/pgbuffercache.sgml @@ -17,10 +17,19 @@ - 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 - convenient use. + The module provides C functions pg_buffercache_pages + and pg_buffercache_summary. + + + + pg_buffercache_pages function + returns a set of records, plus a view pg_buffercache that wraps the function for + convenient use is provided. + + + + pg_buffercache_summary function returns a table with a single row + that contains summarized and aggregated information about shared buffer caches. @@ -164,6 +173,92 @@ + + The <structname>pg_buffercache_summary</structname> Function + + + The definitions of the columns exposed by the function are shown in . + + + + <structname>pg_buffercachesummary</structname> Columns + + + + + Column Type + + + Description + + + + + + + + used_buffers int4 + + + Number of shared buffers currently being used + + + + + + unused_buffers int4 + + + Number of shared buffers that not currently being used + + + + + + dirty_buffers int4 + + + Number of dirty shared buffer caches + + + + + + pinned_buffers int4 + + + Number of shared buffers that has a pinned backend + + + + + + avg_usagecount float + + + Average usagecount of used shared buffers + + + + +
+ + + 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. + + + + Unlike pg_buffercache_pages function + pg_buffercache_summary doesn't take buffer manager + locks and buffer headers locks, thus the result is not consistent. 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. + + + Sample Output @@ -191,6 +286,13 @@ 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(); + used_buffers | unused_buffers | dirty_buffers | pinned_buffers | avg_usagecount +--------------+----------------+---------------+----------------+---------------- + 248 | 2096904 | 39 | 0 | 3.141129 +(1 row) -- 2.37.2