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@ ~]$ psql psql (9.4.1) Type "help" for help. postgres=# create table tbl_kenyon(id int,remark text); CREATE TABLE postgres=# insert into tbl_kenyon select generate_series(1,1000000),md5(random()::text); INSERT 0 1000000 postgres=# 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 1000000 postgres=# \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concurrently postgres=# insert into tbl_kenyon values(1000001,md5(random()::text)); INSERT 0 1 postgres=# 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 VIEW Time: 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 1 Time: 9.434 ms postgres=# refresh materialized view concurrently mv_tbl_kenyon; ERROR: cannot refresh materialized view "public.mv_tbl_kenyon" concurrently HINT: Create a unique index with no WHERE clause on one or more columns of the materialized view. Time: 22109.877 ms postgres=# create unique index idx_ken on mv_tbl_kenyon(id); CREATE INDEX Time: 707.721 ms postgres=# select max(id) from mv_tbl_kenyon ; max --------- 1000001 (1 row) Time: 1.110 ms postgres=# begin; BEGIN postgres=# refresh materialized view concurrently mv_tbl_kenyon; REFRESH MATERIALIZED VIEW Time: 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false foundUniqueIndex = false; --如果找到唯一索引赋值为true if (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error if (!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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