PostgreSQL DBA(83) - Extension(pg_buffercache)

使用pg_buffercache插件可查看shared buffer中的内容.

安装pg_buffercache

[pg12@localhost pg_buffercache]$ makemake -C ../../src/backend generated-headersmake[1]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend'make -C catalog distprep generated-header-symlinksmake[2]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend/catalog'make[2]: Nothing to be done for `distprep'.make[2]: Nothing to be done for `generated-header-symlinks'.make[2]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend/catalog'make -C utils distprep generated-header-symlinksmake[2]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend/utils'make[2]: Nothing to be done for `distprep'.make[2]: Nothing to be done for `generated-header-symlinks'.make[2]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend/utils'make[1]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend'gcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O0 -DOPTIMIZER_DEBUG -g3 -gdwarf-2 -fPIC -I. -I. -I../../src/include  -D_GNU_SOURCE -I/usr/include/libxml2   -c -o pg_buffercache_pages.o pg_buffercache_pages.c -MMD -MP -MF .deps/pg_buffercache_pages.Pogcc -std=gnu99 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -g -O0 -DOPTIMIZER_DEBUG -g3 -gdwarf-2 -fPIC -shared -o pg_buffercache.so pg_buffercache_pages.o  -L../../src/port -L../../src/common    -Wl,--as-needed -Wl,-rpath,'/appdb/pg12/pg12beta3/lib',--enable-new-dtags  [pg12@localhost pg_buffercache]$ sudo make install[sudo] password for pg12: make -C ../../src/backend generated-headersmake[1]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend'make -C catalog distprep generated-header-symlinksmake[2]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend/catalog'make[2]: Nothing to be done for `distprep'.make[2]: Nothing to be done for `generated-header-symlinks'.make[2]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend/catalog'make -C utils distprep generated-header-symlinksmake[2]: Entering directory `/home/pg12/source/postgresql-12beta3/src/backend/utils'make[2]: Nothing to be done for `distprep'.make[2]: Nothing to be done for `generated-header-symlinks'.make[2]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend/utils'make[1]: Leaving directory `/home/pg12/source/postgresql-12beta3/src/backend'/bin/mkdir -p '/appdb/pg12/pg12beta3/lib/postgresql'/bin/mkdir -p '/appdb/pg12/pg12beta3/share/postgresql/extension'/bin/mkdir -p '/appdb/pg12/pg12beta3/share/postgresql/extension'/bin/install -c -m 755  pg_buffercache.so '/appdb/pg12/pg12beta3/lib/postgresql/pg_buffercache.so'/bin/install -c -m 644 ./pg_buffercache.control '/appdb/pg12/pg12beta3/share/postgresql/extension/'/bin/install -c -m 644 ./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--unpackaged--1.0.sql  '/appdb/pg12/pg12beta3/share/postgresql/extension/'[pg12@localhost pg_buffercache]$

简单使用

[local]:5432 pg12@testdb=# create extension pg_buffercachepg12@testdb-# ;CREATE EXTENSIONTime: 149.794 ms[local]:5432 pg12@testdb=# \d pg_buffercache                 View "public.pg_buffercache"      Column      |   Type   | Collation | Nullable | Default ------------------+----------+-----------+----------+--------- bufferid         | integer  |           |          |  relfilenode      | oid      |           |          |  reltablespace    | oid      |           |          |  reldatabase      | oid      |           |          |  relforknumber    | smallint |           |          |  relblocknumber   | bigint   |           |          |  isdirty          | boolean  |           |          |  usagecount       | smallint |           |          |  pinning_backends | integer  |           |          | [local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# select * from pg_buffercache;-[ RECORD 1 ]----+------bufferid         | 1relfilenode      | 33029reltablespace    | 1664reldatabase      | 0relforknumber    | 0relblocknumber   | 0isdirty          | fusagecount       | 5pinning_backends | 0-[ RECORD 2 ]----+------bufferid         | 2relfilenode      | 32825reltablespace    | 1664reldatabase      | 0relforknumber    | 0relblocknumber   | 0isdirty          | fusagecount       | 4pinning_backends | 0...

直接查询pg_buffercache可获得shared buffer的相关信息.
创建统计视图

create or replace view vw_buffercache_hogs asselect case       when pg_buffercache.reldatabase = 0            then '- global'       when pg_buffercache.reldatabase <> (select pg_database.oid from pg_database where pg_database.datname = current_database())            then '- database ' || quote_literal(pg_database.datname)       when pg_namespace.nspname = 'pg_catalog'            then '- system catalogues'       when pg_class.oid is null and pg_buffercache.relfilenode > 0            then '- unknown file ' || pg_buffercache.relfilenode       when pg_namespace.nspname = 'pg_toast' and pg_class.relname ~ '^pg_toast_[0-9]+$'            then (substring(pg_class.relname, 10)::oid)::regclass || ' TOAST'::text       when pg_namespace.nspname = 'pg_toast' and pg_class.relname ~ '^pg_toast_[0-9]+_index$'            then ((rtrim(substring(pg_class.relname, 10), '_index'))::oid)::regclass || ' TOAST index'       else pg_class.oid::regclass::text       end as key,       count(*) as buffers, sum(case when pg_buffercache.isdirty then 1 else 0 end) as dirty_buffers,       round(count(*) / (SELECT pg_settings.setting FROM pg_settings WHERE pg_settings.name = 'shared_buffers')::numeric, 4) as hog_factorfrom pg_buffercache     left join pg_database on pg_database.oid = pg_buffercache.reldatabase     left join pg_class on pg_class.relfilenode = pg_buffercache.relfilenode     left join pg_namespace on pg_namespace.oid = pg_class.relnamespacegroup by 1order by 2 desc;

查询该视图

[local]:5432 pg12@testdb=# create or replace view vw_buffercache_hogs aspg12@testdb-# select casepg12@testdb-#        when pg_buffercache.reldatabase = 0pg12@testdb-#             then '- global'pg12@testdb-#        when pg_buffercache.reldatabase <> (select pg_database.oid from pg_database where pg_database.datname = current_database())pg12@testdb-#             then '- database ' || quote_literal(pg_database.datname)pg12@testdb-#        when pg_namespace.nspname = 'pg_catalog'pg12@testdb-#             then '- system catalogues'pg12@testdb-#        when pg_class.oid is null and pg_buffercache.relfilenode > 0pg12@testdb-#             then '- unknown file ' || pg_buffercache.relfilenodepg12@testdb-#        when pg_namespace.nspname = 'pg_toast' and pg_class.relname ~ '^pg_toast_[0-9]+$'pg12@testdb-#             then (substring(pg_class.relname, 10)::oid)::regclass || ' TOAST'::textpg12@testdb-#        when pg_namespace.nspname = 'pg_toast' and pg_class.relname ~ '^pg_toast_[0-9]+_index$'pg12@testdb-#             then ((rtrim(substring(pg_class.relname, 10), '_index'))::oid)::regclass || ' TOAST index'pg12@testdb-#        else pg_class.oid::regclass::textpg12@testdb-#        end as key,pg12@testdb-#        count(*) as buffers, sum(case when pg_buffercache.isdirty then 1 else 0 end) as dirty_buffers,pg12@testdb-#        round(count(*) / (SELECT pg_settings.setting FROM pg_settings WHERE pg_settings.name = 'shared_buffers')::numeric, 4) as hog_factorpg12@testdb-# from pg_buffercachepg12@testdb-#      left join pg_database on pg_database.oid = pg_buffercache.reldatabasepg12@testdb-#      left join pg_class on pg_class.relfilenode = pg_buffercache.relfilenodepg12@testdb-#      left join pg_namespace on pg_namespace.oid = pg_class.relnamespacepg12@testdb-# group by 1pg12@testdb-# order by 2 desc;CREATE VIEWTime: 69.892 ms[local]:5432 pg12@testdb=# select * from vw_buffercache_hogs;           key            | buffers | dirty_buffers | hog_factor --------------------------+---------+---------------+------------                          |   65187 |             0 |     0.9947 - system catalogues      |     174 |            22 |     0.0027 - unknown file 32856     |      32 |             1 |     0.0005 - unknown file 32861     |      28 |             2 |     0.0004 - global                 |      19 |             0 |     0.0003 - unknown file 32869     |      15 |             4 |     0.0002 - unknown file 32868     |      11 |             1 |     0.0002 t_copy                   |       8 |             0 |     0.0001 - unknown file 32867     |       8 |             1 |     0.0001 - unknown file 32860     |       8 |             1 |     0.0001 - unknown file 32873     |       7 |             2 |     0.0001 - unknown file 32809     |       7 |             1 |     0.0001 - unknown file 32816     |       6 |             3 |     0.0001 - unknown file 32872     |       5 |             1 |     0.0001 pg_rewrite TOAST         |       4 |             3 |     0.0001 - unknown file 32815     |       4 |             1 |     0.0001 - unknown file 32874     |       4 |             1 |     0.0001 - unknown file 32859     |       3 |             1 |     0.0000 pg_rewrite TOAST index   |       2 |             1 |     0.0000 pg_statistic TOAST index |       2 |             0 |     0.0000 t_import                 |       1 |             0 |     0.0000 pg_statistic TOAST       |       1 |             0 |     0.0000(22 rows)Time: 201.894 ms

另外,关于索引创建后,索引数据是否已缓存在shared buffer,答案是否定的.

[local]:5432 pg12@testdb=# create index idx_t_prewarm_id on t_prewarm(id);CREATE INDEXTime: 578.582 ms[local]:5432 pg12@testdb=# select * from vw_buffercache_hogs;          key           | buffers | dirty_buffers | hog_factor ------------------------+---------+---------------+------------                        |   59920 |             0 |     0.9143 t_prewarm              |    5406 |             0 |     0.0825 - system catalogues    |      82 |             6 |     0.0013 - unknown file 32856   |      32 |             2 |     0.0005 - unknown file 32861   |      19 |             0 |     0.0003 - unknown file 32869   |      14 |             1 |     0.0002 - global               |      14 |             0 |     0.0002 - unknown file 32867   |       8 |             0 |     0.0001 - unknown file 32860   |       8 |             1 |     0.0001 - unknown file 32872   |       5 |             1 |     0.0001 - unknown file 32873   |       4 |             1 |     0.0001 - unknown file 32816   |       4 |             0 |     0.0001 - unknown file 32868   |       4 |             0 |     0.0001 - unknown file 32859   |       3 |             1 |     0.0000 - unknown file 32809   |       3 |             0 |     0.0000 - unknown file 32815   |       3 |             0 |     0.0000 - unknown file 32874   |       3 |             1 |     0.0000 pg_rewrite TOAST index |       2 |             0 |     0.0000 pg_rewrite TOAST       |       2 |             0 |     0.0000(19 rows)Time: 221.542 ms

在预热后才会在内存中

[local]:5432 pg12@testdb=# select pg_prewarm('idx_t_prewarm_id'); pg_prewarm ------------       2745(1 row)Time: 51.211 ms[local]:5432 pg12@testdb=# select * from vw_buffercache_hogs;          key           | buffers | dirty_buffers | hog_factor ------------------------+---------+---------------+------------                        |   62601 |             0 |     0.9552 idx_t_prewarm_id       |    2745 |             0 |     0.0419 - system catalogues    |      69 |             0 |     0.0011 - unknown file 32856   |      31 |             0 |     0.0005 - unknown file 32861   |      18 |             0 |     0.0003 - global               |      14 |             0 |     0.0002 - unknown file 32869   |      11 |             0 |     0.0002 - unknown file 32860   |       8 |             0 |     0.0001 - unknown file 32867   |       8 |             0 |     0.0001 - unknown file 32872   |       5 |             0 |     0.0001 - unknown file 32816   |       4 |             0 |     0.0001 t_prewarm              |       4 |             0 |     0.0001 - unknown file 32873   |       4 |             0 |     0.0001 - unknown file 32815   |       3 |             0 |     0.0000 - unknown file 32868   |       3 |             0 |     0.0000 - unknown file 32809   |       3 |             0 |     0.0000 pg_rewrite TOAST index |       2 |             0 |     0.0000 pg_rewrite TOAST       |       2 |             0 |     0.0000 - unknown file 32874   |       1 |             0 |     0.0000(19 rows)Time: 131.575 ms

参考资料
Postgresql cache (memory) performance + how to warm up the cache