PG 11在插入分区表时,无论涉及多少个分区都会锁住每个分区,如果分区数很多,会存在性能问题.在PG 12,只需要对涉及的分区上锁,也就是说如果只插入一行,则只需要锁一个分区.这种变化还与分区元组路由代码的完全重写相结合,大大减少了在executor启动期间设置元组路由数据结构的开销。 **创建分区表** ``` [local]:5432 pg12@testdb=# drop table if exists t_counter; NOTICE: table "t_counter" does not exist, skipping DROP TABLE Time: 29.768 ms [local]:5432 pg12@testdb=# create table t_counter(id int); CREATE TABLE Time: 120.165 ms [local]:5432 pg12@testdb=# insert into t_counter select generate_series(0,100000); INSERT 0 100001 Time: 333.637 ms [local]:5432 pg12@testdb=# drop table if exists t_hash_manypartitions; NOTICE: table "t_hash_manypartitions" does not exist, skipping DROP TABLE Time: 1.536 ms [local]:5432 pg12@testdb=# create table t_hash_manypartitions (c1 int,c2 varchar(40),c3 varchar(40)) partition by hash(c2); CREATE TABLE Time: 45.986 ms [local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# \o /tmp/script.sql [local]:5432 pg12@testdb=# select 'create table t_hash_manypartitions_' pg12@testdb-# ||id pg12@testdb-# ||' partition of t_hash_manypartitions for values with (modulus 8192,remainder '||id||');' pg12@testdb-# from t_counter pg12@testdb-# where id < 8192 pg12@testdb-# order by id ; Time: 78.499 ms [local]:5432 pg12@testdb=# \o [local]:5432 pg12@testdb=# [root@localhost ~]# tail -n 10 /tmp/script.sql create table t_hash_manypartitions_8184 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8184); create table t_hash_manypartitions_8185 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8185); create table t_hash_manypartitions_8186 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8186); create table t_hash_manypartitions_8187 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8187); create table t_hash_manypartitions_8188 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8188); create table t_hash_manypartitions_8189 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8189); create table t_hash_manypartitions_8190 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8190); create table t_hash_manypartitions_8191 partition of t_hash_manypartitions for values with (modulus 8192,remainder 8191); (8192 rows) [local]:5432 pg12@testdb=# \i /tmp/script.sql ... CREATE TABLE Time: 20.784 ms CREATE TABLE Time: 21.107 ms psql:/tmp/script.sql:8196: ERROR: syntax error at or near "8192" LINE 1: (8192 rows) ^ Time: 0.198 ms [local]:5432 pg12@testdb=# ``` **PG 11** 启动事务,插入一行 ``` [xdb@localhost ~]$ psql -d testdb -p 5433 psql (11.2) Type "help" for help. testdb=# \timing Timing is on. testdb=# begin; BEGIN Time: 1.750 ms testdb=# insert into t_hash_manypartitions(c1,c2,c3) values(1,'c2-1','c3-1'); INSERT 0 1 Time: 75.649 ms testdb=# ``` 查询锁信息,锁定了所有分区 ``` testdb=# select relation::regclass,locktype,virtualxid,transactionid,virtualtransaction,pid,mode,granted,fastpath from pg_locks where pid <> pg_backend_pid(); relation | locktype | virtualxid | transactionid | virtualtransaction | pid | mode | granted | fastpath ----------------------------+---------------+------------+---------------+--------------------+------+------------------+---------+---------- t_hash_manypartitions_15 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_14 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_13 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_12 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_11 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_10 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_9 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_8 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_7 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_6 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_5 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_4 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_3 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_2 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions_1 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t t_hash_manypartitions | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | t | virtualxid | 3/8202 | | 3/8202 | 4855 | ExclusiveLock | t | t t_hash_manypartitions_1077 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | f t_hash_manypartitions_3140 | relation | | | 3/8202 | 4855 | RowExclusiveLock | t | f ... testdb=# select count(*) from pg_locks where pid <> pg_backend_pid(); count ------- 8194 (1 row) ``` **PG 12** 启动事务,插入一行 ``` [local]:5432 pg12@testdb=# begin; BEGIN Time: 2.418 ms [local]:5432 pg12@testdb=#* [local]:5432 pg12@testdb=#* insert into t_hash_manypartitions(c1,c2,c3) values(1,'c2-1','c3-1'); INSERT 0 1 Time: 46.988 ms [local]:5432 pg12@testdb=#* ``` 查询锁信息,只锁定一个分区 ``` [local]:5432 pg12@testdb=# select relation::regclass,locktype,virtualxid,transactionid,virtualtransaction,pid,mode,granted,fastpath from pg_locks where pid <> pg_backend_pid(); relation | locktype | virtualxid | transactionid | virtualtransaction | pid | mode | granted | fastpath ----------------------------+---------------+------------+---------------+--------------------+------+------------------+---------+---------- t_hash_manypartitions_4956 | relation | | | 3/8202 | 3230 | RowExclusiveLock | t | t t_hash_manypartitions | relation | | | 3/8202 | 3230 | AccessShareLock | t | t t_hash_manypartitions | relation | | | 3/8202 | 3230 | RowExclusiveLock | t | t | virtualxid | 3/8202 | | 3/8202 | 3230 | ExclusiveLock | t | t | transactionid | | 176799 | 3/8202 | 3230 | ExclusiveLock | t | f (5 rows) Time: 1.596 ms ``` **参考资料** [PostgreSQL 12: Partitioning is now faster ](https://www.2ndquadrant.com/en/blog/postgresql-12-partitioning/)