PostgreSQL删除更新优化操作

1. 先说删除吧，因为刚搞了。

删除缓慢的原因：主要是约束的问题。（数据库在有约束的时候，进行操作，会根据约束对相关表进行验证，可想而知，20w的数据验证要耗费多久的时间）。其次就是sql的编写。（sql如果查询中包含子查询等的可以优化的where会影响匹配的速度<查询的话就不多逼逼了>）。索引的问题 请看下面的 补充部分

具体解决方法：

alter table tablename disable trigger all; 
  delete 目标语句 
alter table tablename enable trigger all;

2. 更新，原因和删除大体一致，这里主要描述一下自己遇到的问题。

利用mybatis批量更新，第一张图是原本的批量更新的写法，发现在本地还可以的但是放在服务器会由于时间太久出现io错误。

后来换成第二张图的方式来更新。当然也可以java代码for循环来单条更新来达到批量的目的。（对于这三种方式，第二种最快）

<update id="batchupdate2" parametertype="java.util.list">
		update lt_dzheinfo 
		 <trim prefix="set" suffixoverrides=",">
   <trim prefix="dzzhao =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readerbarcode}
    </foreach>
   </trim>
   <trim prefix="xming =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readername}
    </foreach>
   </trim>
    <trim prefix="ztai =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readerstate}
    </foreach>
   </trim>
    <trim prefix="mima =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readerpsw}
    </foreach>
   </trim>
   <trim prefix="dzlxid =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readertype}
    </foreach>
   </trim>
   <trim prefix="zjlx =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.identitytype}
    </foreach>
   </trim>
   <trim prefix="zjhma =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.identityid}
    </foreach>
   </trim>
   <trim prefix="qyrqi =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss')
    </foreach>
   </trim>
   <trim prefix="jzrqi =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then to_timestamp(#{reader.disabledate}, 'yyyy-mm-dd hh24:mi:ss')
    </foreach>
   </trim>
   <trim prefix="libid =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readeroflibcode}
    </foreach>
   </trim>
   <trim prefix="xingbie =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
    	when dzid=#{reader.readerid} then 
		   <choose>
						<when test="reader.readersex=='男'.tostring()">
							true
						</when>
						<otherwise>
							false
						</otherwise>
					</choose>
    </foreach>
   </trim>
   <trim prefix="userid =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readeroperatorid}
    </foreach>
   </trim>
   <trim prefix="beizhu =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then #{reader.readerremark}
    </foreach>
   </trim>
   <trim prefix="bzrqi =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss')
    </foreach>
   </trim>
   <trim prefix="optime =case" suffix="end,">
    <foreach collection="list" item="reader" index="index">
      when dzid=#{reader.readerid} then to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss')
    </foreach>
   </trim>
  </trim>
  where dzid in
  <foreach collection="list" index="index" item="reader" separator="," open="(" close=")">
   #{reader.readerid}
  </foreach>
	</update>

<update id="batchupdate" parametertype="java.util.list">
		<foreach collection="list" index="index" item="reader" separator=";">
			update lt_dzheinfo set
			dzzhao = #{reader.readerbarcode},
			xming = #{reader.readername},
			ztai = #{reader.readerstate},
			mima = #{reader.readerpsw},
			dzlxid = #{reader.readertype},
			zjlx = #{reader.identitytype},
			zjhma = #{reader.identityid},
			qyrqi = to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss'),
			jzrqi = to_timestamp(#{reader.disabledate}, 'yyyy-mm-dd hh24:mi:ss'),
			libid = #{reader.readeroflibcode},
			xingbie = 
			<choose>
				<when test="reader.readersex=='男'.tostring()">
					true
				</when>
				<otherwise>
					false
				</otherwise>
			</choose>,
			userid = #{reader.readeroperatorid},
			beizhu = #{reader.readerremark},
			bzrqi = to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss'),
			optime = to_timestamp(#{reader.enabledate}, 'yyyy-mm-dd hh24:mi:ss')
			<where>
				dzid = #{reader.readerid}
			</where>
		</foreach>
	</update>

补充：数据库突然变慢...索引作怪！

本人在最近发现，有些比容量较大的sql数据库，在使用一段时间后，会突然变很慢很慢。特别体现在一些经常进行操作及查询的大表中。经过深入研究，这一般是索引的问题！如果把此表的索引重建一次，问题即可解决。

为更好地解决此问题，建意在sql中新建一个数据库维护计划，选中“重新组织数据各索引页”选项，并设置每天运行一次。

/*
 刷新数据库视图.sql
*/
alter proc p_refreshview
as

declare @vname sysname

declare refresh_cursor cursor for
 select name from sysobjects where xtype = 'v' order by crdate
for read only 
open refresh_cursor

fetch next from refresh_cursor
into @vname
 while @@fetch_status = 0
 begin
--刷新指定视图的元数据。由于视图所依赖的基础对象的更改，视图的持久元数据会过期。
 exec sp_refreshview @vname
 print '视图' + @vname + '已更新'
 fetch next from refresh_cursor
  into @vname
 end
close refresh_cursor
deallocate refresh_cursor

go
set quoted_identifier off
go
set ansi_nulls on
go

以上为个人经验，希望能给大家一个参考，也希望大家多多支持。如有错误或未考虑完全的地方，望不吝赐教。