os: centos 7.4
db: postgresql 10.11
pg_qualstats 是 postgresql 的一個 extension，用於保存"where"語句和"join"子句中謂詞的統計信息。
版本
# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core)
#
#
# yum list installed |grep -i postgresql
postgresql10.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-contrib.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-debuginfo.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-devel.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-docs.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-libs.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-odbc.x86_64 12.00.0000-1PGDG.rhel7 @pgdg10
postgresql10-plperl.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-plpython.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-pltcl.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-server.x86_64 10.11-2PGDG.rhel7 @pgdg10
postgresql10-tcl.x86_64 2.4.0-1.rhel7 @pgdg10
postgresql10-tcl-debuginfo.x86_64 2.3.1-1.rhel7 @pgdg10
postgresql10-test.x86_64 10.11-2PGDG.rhel7 @pgdg10
# su - postgres
Last login: Wed Jan 15 18:34:12 CST 2020 on pts/0
$
$
$ psql -c "select version();"
version
----------------------------------------------------------------------------------------------------------
PostgreSQL 10.11 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)
下載安裝
# yum list all |grep -i pg_qualstats
Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
pg_qualstats10.x86_64 1.0.9-1.rhel7.1 pgdg10
# yum install pg_qualstats10
# repoquery -ql pg_qualstats10
/usr/pgsql-10/doc/extension/README-pg_qualstats.md
/usr/pgsql-10/lib/pg_qualstats.so
/usr/pgsql-10/share/extension/pg_qualstats--2.0.1.sql
/usr/pgsql-10/share/extension/pg_qualstats.control
/usr/share/licenses/pg_qualstats10-2.0.1
/usr/share/licenses/pg_qualstats10-2.0.1/LICENSE
修改配置文件 shared_preload_libraries
# vi /var/lib/pgsql/10/data/postgresql.conf
shared_preload_libraries = 'pg_stat_statements, pg_qualstats'
# systemctl restart postgresql-10.service
初步使用
創建 extension pg_qualstats pg_stat_statements
# su - postgres
$ psql
postgres=# create extension pg_stat_statements;
postgres=# create extension pg_qualstats;
postgres=#
postgres=# \dx
List of installed extensions
Name | Version | Schema | Description
--------------------+---------+------------+-------------------------------------------------------------------
pg_qualstats | 2.0.1 | public | An extension collecting statistics about quals
pg_stat_statements | 1.6 | public | track execution statistics of all SQL statements executed
plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language
(3 rows)
postgres=# \dx+ pg_qualstats
Objects in extension "pg_qualstats"
Object description
-------------------------------------------------------------
function pg_qualstats()
function pg_qualstats_deparse_qual(qual)
function pg_qualstats_example_queries()
function pg_qualstats_example_query(bigint)
function pg_qualstats_get_idx_col(bigint,boolean)
function pg_qualstats_get_qualnode_rel(bigint)
function pg_qualstats_index_advisor(integer,integer,text[])
function pg_qualstats_names()
function pg_qualstats_reset()
type qual
type qualname
view pg_qualstats
view pg_qualstats_all
view pg_qualstats_by_query
view pg_qualstats_pretty
(15 rows)
postgres=# select name,setting from pg_settings where name like 'pg_qualstats%';
name | setting
-------------------------------------+---------
pg_qualstats.enabled | on
pg_qualstats.max | 1000
pg_qualstats.min_err_estimate_num | 0
pg_qualstats.min_err_estimate_ratio | 0
pg_qualstats.resolve_oids | off
pg_qualstats.sample_rate | 0.001
pg_qualstats.track_constants | on
pg_qualstats.track_pg_catalog | off
(8 rows)
postgres=# select name,setting from pg_settings where name like 'pg_stat_statements%';
name | setting
----------------------------------+---------
pg_stat_statements.max | 5000
pg_stat_statements.save | on
pg_stat_statements.track | top
pg_stat_statements.track_utility | on
(4 rows)
pg_qualstats.enabled (boolean, default true): whether or not pg_qualstats should be enabled
pg_qualstats.max: the maximum number of predicated and query text tracked (defaults to 1000)
pg_qualstats.resolve_oids (boolean, default false): whether or not pg_qualstats should resolve oids at query time, or juste store the oids. Enabling this parameter makes the data analysis much more easy, since a connection to the database where the query was executed won’t be necessary, but it will eat much more space (624 bytes per entry instead of 176). Additionnaly, this will require some catalog lookups, which aren’t free.
pg_qualstats.sample_rate (double, default -1): the fraction of queries that should be sampled. For example, 0.1 means that only one out of ten queries will be sampled. The default (-1) means automatic, and results in a value of 1 / max_connections, so that statiscally, concurrency issues will be rare.
pg_qualstats.track_constants (bolean, default true): whether or not pg_qualstats should keep track of each constant value individually. Disabling this GUC will considerably reduce the number of entries necessary to keep track of predicates.
pg_qualstats.track_pg_catalog (boolean, default false): whether or not pg_qualstats should compute predicates on object in pg_catalog schema.
生成測試表
postgres=# create table tmp_t0(id int8,name1 varchar(100),name2 varchar(100));
postgres=# create table tmp_t1(id int8,name1 varchar(100),name2 varchar(100));
postgres=#
postgres=# insert into tmp_t0
select id,md5(id::varchar),md5(md5(id::varchar)) from generate_series(1,1000000) as id;
postgres=# insert into tmp_t1
select id,md5(id::varchar),md5(md5(id::varchar)) from generate_series(1,1000000) as id;
postgres=# set pg_qualstats.sample_rate=1;
postgres=# select t0.*,t1.* from tmp_t0 t0,tmp_t1 t1 where t0.id=t1.id and t0.id<=10;
pg_qualstats.sample_rate=1 會確保所有的query都會被抓取到.
查看 pg_stat_statements
postgres=# \x
postgres=# select * from pg_stat_statements where query like '%t0.id%';
-[ RECORD 1 ]-------+--------------------------------------------------------------------------
userid | 10
dbid | 13808
queryid | 3486472503
query | select t0.*,t1.* from tmp_t0 t0,tmp_t1 t1 where t0.id=t1.id and t0.id<=$1
calls | 6
total_time | 1877.331149
min_time | 299.02719
max_time | 336.694227
mean_time | 312.888524833333
stddev_time | 12.7704381729133
rows | 150
shared_blks_hit | 321027
shared_blks_read | 0
shared_blks_dirtied | 0
shared_blks_written | 0
local_blks_hit | 0
local_blks_read | 0
local_blks_dirtied | 0
local_blks_written | 0
temp_blks_read | 0
temp_blks_written | 0
blk_read_time | 0
blk_write_time | 0
postgres=# with table_info as (
select pc.relname,pgq.execution_count,pgq.uniquequalnodeid
from pg_qualstats as pgq
left join pg_class as pc on pgq.lrelid = pc.relfilenode
),query_info as (
select pss.total_time/calls as average_time,pss.query,pgb.uniquequalnodeid
from pg_qualstats_by_query as pgb
left join pg_stat_statements as pss on pgb.queryid = pss.queryid
)
select *
from table_info as t
right join query_info as q on t.uniquequalnodeid = q.uniquequalnodeid;
-[ RECORD 1 ]----+--------------------------------------------------------------------------
relname | tmp_t0
execution_count | 3000000
uniquequalnodeid | 2803249348
average_time | 441.271635
query | select t0.*,t1.* from tmp_t0 t0,tmp_t1 t1 where t0.id=t1.id and t0.id<=$1
uniquequalnodeid | 2803249348
參考：
https://www.postgresql.org/download/products/5-reporting-tools/
https://github.com/powa-team/pg_qualstats/