PostgreSQL 9.4版本的物化视图更新

PostgreSQL的9.4版本出来有一段时间了，也更新了很多内容，其中之一是比较感兴趣的物化视图的更新，对比原先的物化视图语法，新增

PostgreSQL的9.4版本出来有一段时间了，也更新了很多内容，其中之一是比较感兴趣的物化视图的更新，对比原先的物化视图语法，新增了一个CONCURRENTLY参数。

一、新语法：

--创建语法,未有更新CREATE MATERIALIZED VIEW table_name[ (column_name [, ...] ) ][ WITH ( storage_parameter [= value] [, ... ] ) ][ TABLESPACE tablespace_name ]AS query[ WITH [ NO ] DATA ]--刷新语法REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] name[ WITH [ NO ] DATA ]

二、数据准备：

[postgres@ ~]$ psqlpsql (9.4.1)Type "help" for help.postgres=# create table tbl_kenyon(id int,remark text);CREATE TABLEpostgres=# insert into tbl_kenyon select generate_series(1,1000000),md5(random()::text);INSERT 0 1000000postgres=# select * from tbl_kenyon limit 10; id |remark----+---------------------------------- 1 | d4fc1c7440a4d1672028586c2bb76514 2 | 5c1590519fa47f02db2895146a5f62a4 3 | 1710ac4199746e9bfa188f1655d1f857 4 | 6cae64191c2bc309a4884301e77b26ad 5 | 813987a5c3af2d75bd0de6e288083b10 6 | c52baa42cda22c89719bfb59dde1f78b 7 | 491003337ea4e887c5ac24d174c691c6 8 | 455cdf32b170fcf2b450c0b974fbf310 9 | 43adb30aeb0a21ab35fdf97064ad1d21 10 | 97dc1adc5484244a077e87ef36ecfe09(10 rows)--创建简单的物化视图postgres=# create materialized view mv_tbl_kenyon as select * from tbl_kenyon ;SELECT 1000000postgres=# \d+List of relations Schema |Name|Type| Owner | Size | Description --------+---------------+-------------------+----------+-------+------------- public | mv_tbl_kenyon | materialized view | postgres | 65 MB | public | tbl_kenyon | table| postgres | 65 MB | (2 rows)

三、测试用例:

--测试不带concurrentlypostgres=# insert into tbl_kenyon values(1000001,md5(random()::text));INSERT 0 1postgres=# select max(id) from mv_tbl_kenyon ;max--------- 1000000(1 row)postgres=# \timing Timing is on.postgres=# refresh materialized view mv_tbl_kenyon ;REFRESH MATERIALIZED VIEWTime: 2056.460 ms--测试带concurrently，需要建一个唯一索引postgres=# insert into tbl_kenyon values(1000002,md5(random()::text));INSERT 0 1Time: 9.434 mspostgres=# refresh materialized view concurrently mv_tbl_kenyon;ERROR: cannot refresh materialized view "public.mv_tbl_kenyon" concurrentlyHINT: Create a unique index with no WHERE clause on one or more columns of the materialized view.Time: 22109.877 mspostgres=# create unique index idx_ken on mv_tbl_kenyon(id);CREATE INDEXTime: 707.721 mspostgres=# select max(id) from mv_tbl_kenyon ;max--------- 1000001(1 row)Time: 1.110 mspostgres=# begin;BEGINpostgres=# refresh materialized view concurrently mv_tbl_kenyon;REFRESH MATERIALIZED VIEWTime: 24674.739 ms--如果在refresh的时候，前面加个begin;--还能发现在开启的另外的session里面，是不会阻塞查询的,反之不加concurrently会阻塞postgres=# select * from mv_tbl_kenyon limit 10; id |remark----+---------------------------------- 1 | d4fc1c7440a4d1672028586c2bb76514 2 | 5c1590519fa47f02db2895146a5f62a4 3 | 1710ac4199746e9bfa188f1655d1f857 4 | 6cae64191c2bc309a4884301e77b26ad 5 | 813987a5c3af2d75bd0de6e288083b10 6 | c52baa42cda22c89719bfb59dde1f78b 7 | 491003337ea4e887c5ac24d174c691c6 8 | 455cdf32b170fcf2b450c0b974fbf310 9 | 43adb30aeb0a21ab35fdf97064ad1d21 10 | 97dc1adc5484244a077e87ef36ecfe09(10 rows)

四、源码
相关唯一索引的源码，在matview.c里面可以查看：

--先初始化唯一索引是falsefoundUniqueIndex = false;--如果找到唯一索引赋值为trueif (foundUniqueIndex)appendStringInfoString(&querybuf, " AND ");colname = quote_identifier(NameStr((tupdesc->attrs[attnum - 1])->attname));appendStringInfo(&querybuf, "newdata.%s ", colname);type = attnumTypeId(matviewRel, attnum);op = lookup_type_cache(type, TYPECACHE_EQ_OPR)->eq_opr;mv_GenerateOper(&querybuf, op);appendStringInfo(&querybuf, " mv.%s", colname);foundUniqueIndex = true;--如果找不到唯一索引报errorif (!foundUniqueIndex)ereport(ERROR,(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),errmsg("cannot refresh materialized view \"%s\" concurrently",matviewname),errhint("Create a unique index with no WHERE clause on one or more columns of the materialized view.")));appendStringInfoString(&querybuf, " AND newdata OPERATOR(pg_catalog.*=) mv) ""WHERE newdata IS NULL OR mv IS NULL " "ORDER BY tid");

五、总结：
1.新版的物化视图新增了concurrently参数，可以使在刷新视图时不会锁住该物化视图的查询工作
2.该参数的原理和优缺点与索引的concurrently类似，以时间来换取查询锁，，刷新的速度会变得很慢
3.增量刷新的参数还没有，比较遗憾

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