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：
相关唯一索引的源码，在matview.c里面可以查看：
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 ,会对9.4之后，9.3之前的物化视图的查询，其会阻塞有关物化视图的查询
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
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 ,会对9.4之后，9.3之前的物化视图的查询，其会阻塞有关物化视图的查询
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
