加入收藏 | 设为首页 | 会员中心 | 我要投稿 李大同 (https://www.lidatong.com.cn/)- 科技、建站、经验、云计算、5G、大数据,站长网!
当前位置: 首页 > 百科 > 正文

PostgreSQL 9.4版本的物化视图更新

发布时间:2020-12-13 18:14:17 所属栏目:百科 来源:网络整理
导读: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 [,...] ) ]
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

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

(编辑:李大同)

【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容!

    推荐文章
      热点阅读