如何使这篇文章中描述的查询更快,特别是使用可用的RAM制作Postgresql？ – 请注意,我已尝试正确配置effective_cache_size和shared_buffers.见下文.
背景
我必须定期加入一个约2.6亿行表(coreg_master),其中包含新数据.我已经对表进行了分区,以使每个分区都适合RAM.我当然也有适当的索引设置.但是,当分区表与其他(小得多)表分开加入时,它在磁盘上执行完全随机的IO.这是由于大表上的嵌套循环索引扫描,由于我们没有很好的磁盘设置,因此非常慢.
我希望它使用所有可用的RAM来缓存大型分区表,我理解应该由Linux内核/文件系统本身来完成.但它仍然没有将表加载到RAM中,尽管它适合.我想这是因为访问模式不是顺序的,因此不会触发缓存？我不知道.查询计划和配置参数如下.
表结构
这是我的大表coreg_master的一个分区.分区表名为coreg_a,coreg_b等.
\d coreg_a
Table "public.coreg_a"
Column | Type | Modifiers
-------------+-------------------+-----------------------------------------------------------
id | integer | not null default nextval('coreg_master_id_seq'::regclass)
first_name | character varying |
last_name | character varying |
phone | character varying |
city | character varying |
zip | integer |
address | character varying |
dob | date |
ip | character varying |
source | character varying |
gender | character varying |
state | character varying |
record_date | date |
email | character varying |
Indexes:
"coreg_a_name" btree (lower(first_name::text),lower(last_name::text))
Check constraints:
"coreg_a_first_name_check" CHECK (first_name::text >= 'a'::text AND first_name::text < 'b'::text)
Inherits: coreg_master
以下是表appendable_24的分区,该表是与coreg_master连接的表的示例.它的分区方式与coreg_master相同,所以实际上coreg_a与appendable_24_a等一起加入,一次一个.
\d appendable_24_a
Table "public.appendable_24_a"
Column | Type | Modifiers
------------+-------------------+-----------
line_num | integer | not null
first_name | character varying |
last_name | character varying |
address | character varying |
state | character varying |
zip | integer |
Indexes:
"appendable_24_a_name_index" btree (lower(first_name::text),lower(last_name::text))
Check constraints:
"appendable_24_a_first_name_check" CHECK (first_name::text >= 'a'::text AND first_name::text < 'b'::text)
Inherits: appendable_24
查询&解释分析
下面是最小连接的解释分析的输出(表根据first_name列的第一个字母进行分区),因为它不需要很长时间.但是,查询计划对于每个分区上的所有连接都是相同的,因此它应该代表较大的连接(注意,我对表进行了分析,总时间实际上是20秒,但在此处更快,因为结果被缓存)：
explain analyze SELECT
coreg_x.phone,coreg_x.email,coreg_x.record_date,appendable_24_x.line_num
FROM appendable_24_x INNER JOIN coreg_x ON
lower(appendable_24_x.first_name) = lower(coreg_x.first_name) AND
lower(appendable_24_x.last_name) = lower(coreg_x.last_name) AND
(coreg_x.phone IS NOT NULL OR coreg_x.email IS NOT NULL) AND
similarity(lower(appendable_24_x.address),lower(coreg_x.address)) > 0.7
;
QUE
RY PLAN
------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------
-----
Nested Loop (cost=0.01..640.49 rows=875 width=39) (actual time=9.990..53.839 rows=29 loo
ps=1)
Join Filter: (similarity(lower((appendable_24_x.address)::text),lower((coreg_x.address
)::text)) > 0.7::double precision)
-> Seq Scan on appendable_24_x (cost=0.00..1.80 rows=80 width=34) (actual time=0.009.
.0.111 rows=80 loops=1)
-> Index Scan using coreg_x_name on coreg_x (cost=0.01..7.95 rows=1 width=64) (actual
time=0.024..0.137 rows=44 loops=80)
Index Cond: ((lower((coreg_x.first_name)::text) = lower((appendable_24_x.first_na
me)::text)) AND (lower((coreg_x.last_name)::text) = lower((appendable_24_x.last_name)::tex
t)))
Filter: ((coreg_x.phone IS NOT NULL) OR (coreg_x.email IS NOT NULL))
Total runtime: 53.950 ms
(7 rows)
一些统计信息,配置参数和其他数据
> Postgresql版本：8.4.4
>操作系统：CentOS 5.5版(最终版)
>文件系统：ext3
>可用内存总量：8GB
> shared_buffers = 2GB
> effective_cache_size = 7200MB
>通过show all：http://pastie.org/1159746完整运行时配置
>最大分区coreg表(coreg_j)大小：~4900MB
>相应的行数：~3200万
>对应的(first_name,last_name)索引大小：~1000MB
>第二个分区表(appendable_24_j)大小：~1800kB
> appendable_24_j中的行：~25,000
