本文简单介绍了PostgreSQL的插件：pg_cron。该插件可在PG中实现类似crontab的功能。
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安装
编译安装
[pg12@localhost pg_cron]$git clone https://github.com/citusdata/pg_cron.git
[pg12@localhost pg_cron]$cd pg_cron
[pg12@localhost pg_cron]$ make
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 -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-implicit-fallthrough -Iinclude -I/appdb/pg12/pg12.1/include -I. -I./ -I/appdb/pg12/pg12.1/include/postgresql/server -I/appdb/pg12/pg12.1/include/postgresql/internal -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/pg_cron.o src/pg_cron.c -MMD -MP -MF .deps/pg_cron.Po
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 -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-implicit-fallthrough -Iinclude -I/appdb/pg12/pg12.1/include -I. -I./ -I/appdb/pg12/pg12.1/include/postgresql/server -I/appdb/pg12/pg12.1/include/postgresql/internal -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/job_metadata.o src/job_metadata.c -MMD -MP -MF .deps/job_metadata.Po
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 -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-implicit-fallthrough -Iinclude -I/appdb/pg12/pg12.1/include -I. -I./ -I/appdb/pg12/pg12.1/include/postgresql/server -I/appdb/pg12/pg12.1/include/postgresql/internal -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/misc.o src/misc.c -MMD -MP -MF .deps/misc.Po
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 -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-implicit-fallthrough -Iinclude -I/appdb/pg12/pg12.1/include -I. -I./ -I/appdb/pg12/pg12.1/include/postgresql/server -I/appdb/pg12/pg12.1/include/postgresql/internal -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/task_states.o src/task_states.c -MMD -MP -MF .deps/task_states.Po
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 -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-implicit-fallthrough -Iinclude -I/appdb/pg12/pg12.1/include -I. -I./ -I/appdb/pg12/pg12.1/include/postgresql/server -I/appdb/pg12/pg12.1/include/postgresql/internal -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/entry.o src/entry.c -MMD -MP -MF .deps/entry.Po
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 -shared -o pg_cron.so src/pg_cron.o src/job_metadata.o src/misc.o src/task_states.o src/entry.o -L/appdb/pg12/pg12.1/lib -Wl,--as-needed -Wl,-rpath,'/appdb/pg12/pg12.1/lib',--enable-new-dtags -L/appdb/pg12/pg12.1/lib -lpq
cat pg_cron.sql > pg_cron--1.0.sql
[pg12@localhost pg_cron]$ make install
/bin/mkdir -p '/appdb/pg12/pg12.1/lib/postgresql'
/bin/mkdir -p '/appdb/pg12/pg12.1/share/postgresql/extension'
/bin/mkdir -p '/appdb/pg12/pg12.1/share/postgresql/extension'
/bin/install -c -m 755 pg_cron.so '/appdb/pg12/pg12.1/lib/postgresql/pg_cron.so'
/bin/install -c -m 644 .//pg_cron.control '/appdb/pg12/pg12.1/share/postgresql/extension/'
/bin/install -c -m 644 .//pg_cron--1.0--1.1.sql .//pg_cron--1.1--1.2.sql pg_cron--1.0.sql '/appdb/pg12/pg12.1/share/postgresql/extension/'
[pg12@localhost pg_cron]$
体验
创建扩展
[local:/data/run/pg12]:5120 pg12@testdb=# create extension pg_cron;
ERROR: can only create extension in database postgres
DETAIL: Jobs must be scheduled from the database configured in cron.database_name, since the pg_cron background worker reads job descriptions from this database.
HINT: Add cron.database_name = 'testdb' in postgresql.conf to use the current database.
CONTEXT: PL/pgSQL function inline_code_block line 4 at RAISE
[local:/data/run/pg12]:5120 pg12@testdb=#
[local:/data/run/pg12]:5120 pg12@testdb=# \c postgres
You are now connected to database "postgres" as user "pg12".
[local:/data/run/pg12]:5120 pg12@postgres=# create extension pg_cron;
CREATE EXTENSION
[local:/data/run/pg12]:5120 pg12@postgres=#
修改系统参数
[local:/data/run/pg12]:5120 pg12@postgres=# select name,setting from pg_settings where name like '%cron%';
name | setting
-----------------------+-----------
cron.database_name | postgres
cron.host | localhost
cron.log_statement | on
cron.max_running_jobs | 32
(4 rows)
[local:/data/run/pg12]:5120 pg12@postgres=#
创建job，目的是每个1分钟执行VACUUM FULL
[local:/data/run/pg12]:5120 pg12@postgres=# SELECT cron.schedule('*/1 * * * *', 'VACUUM FULL');
schedule
----------
1
(1 row)
[local:/data/run/pg12]:5120 pg12@postgres=#
[local:/data/run/pg12]:5120 pg12@postgres=# \df cron.schedule
List of functions
Schema | Name | Result data type | Argument data types | Type
--------+----------+------------------+-----------------------------+------
cron | schedule | bigint | schedule text, command text | func
(1 row)
[local:/data/run/pg12]:5120 pg12@postgres=#
[local:/data/run/pg12]:5120 pg12@postgres=# \df cron.*
List of functions
Schema | Name | Result data type | Argument data types | Type
--------+----------------------+------------------+-----------------------------+------
cron | job_cache_invalidate | trigger | | func
cron | schedule | bigint | schedule text, command text | func
cron | unschedule | boolean | job_id bigint | func
(3 rows)
日志输出
2020-02-11 17:52:59.935 CST,"pg12","postgres",23764,"[local]",5e427932.5cd4,1,"SELECT",2020-02-11 17:51:46 CST,3/8,0,LOG,00000,"failed to parse entry 1",,,,,,"SELECT cron.schedule('0/1 * * * *', 'VACUUM FULL');",,,"psql"
2020-02-11 17:52:59.936 CST,"pg12","postgres",23764,"[local]",5e427932.5cd4,2,"SELECT",2020-02-11 17:51:46 CST,3/8,0,ERROR,22023,"invalid schedule: 0/1 * * * *",,,,,,"SELECT cron.schedule('0/1 * * * *', 'VACUUM FULL');",,,"psql"
2020-02-11 17:54:00.001 CST,,,19164,,5e426547.4adc,2,,2020-02-11 16:26:47 CST,1/0,0,LOG,00000,"cron job 1 starting: VACUUM FULL",,,,,,,,,""
2020-02-11 17:54:00.740 CST,,,19164,,5e426547.4adc,3,,2020-02-11 16:26:47 CST,1/0,0,LOG,00000,"cron job 1 completed: VACUUM ",,,,,,,,,""
2020-02-11 17:55:00.002 CST,,,19164,,5e426547.4adc,4,,2020-02-11 16:26:47 CST,1/0,0,LOG,00000,"cron job 1 starting: VACUUM FULL",,,,,,,,,""
2020-02-11 17:55:00.579 CST,,,19164,,5e426547.4adc,5,,2020-02-11 16:26:47 CST,1/0,0,LOG,00000,"cron job 1 completed: VACUUM ",,,,,,,,,""
取消调度
[local:/data/run/pg12]:5120 pg12@postgres=# select cron.unschedule(1);
unschedule
------------
t
(1 row)
[local:/data/run/pg12]:5120 pg12@postgres=#
参考资料
pg_cron
