--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 六、参考： 1.http://www.postgresql.org/docs/9.4/static/sql-creatematerializedview.html 2.http://francs3.blog.163.com/blog/static/405767272014421104127225/ 3.src/backend/commands/matview.c 4.http://my.oschina.net/Kenyon/blog/161001