Postgresql:在不同的客户端中查询速度慢10倍

Question

查看postgres服务器日志,我发现从Linux客户端或Windows客户端调用时,同一postgres服务器上的完全相同的查询需要更长的时间(大约长10倍).

查询来自运行在具有4GB RAM的Linux机器上的Django应用程序以及具有8GB RAM的Windows机器上.两个pyhon环境都有psycopg2库版本2.4.4将请求发送到同一postgres服务器.

以下是postgres服务器日志

windows查询(带时间):

2013-06-11 12:12:19 EEST [unknown] 10.1.3.152(56895) mferreiraLOG:  duration: 3207.195 ms  statement: SELECT "autotests_tracerperformance"."id", "autotests_tracerperformance"."date", "autotests_tracerperformance"."video_id", "autotests_tracerperformance"."revision_id", "autotests_tracerperformance"."computer_id", "autotests_tracerperformance"."probe", "autotests_tracerperformance"."time_tostart", "autotests_tracerperformance"."hang_atstart", "autotests_tracerperformance"."time_tohang", "autotests_tracerperformance"."hang", "autotests_tracerperformance"."crash", "autotests_tracerperformance"."stacktrace", "autotests_tracerperformance"."framemax", "autotests_tracerperformance"."maxtime", "autotests_tracerperformance"."avgtime" FROM "autotests_tracerperformance" INNER JOIN "revisions" ON ("autotests_tracerperformance"."revision_id" = "revisions"."id") WHERE ("autotests_tracerperformance"."computer_id" = 61  AND "revisions"."repo" = 'Trunk' )

linux查询(更长):

2013-06-11 12:12:56 EEST [unknown] 10.1.3.154(35325) mferreiraLOG:  duration: 22191.773 ms  statement: SELECT "autotests_tracerperformance"."id", "autotests_tracerperformance"."date", "autotests_tracerperformance"."video_id", "autotests_tracerperformance"."revision_id", "autotests_tracerperformance"."computer_id", "autotests_tracerperformance"."probe", "autotests_tracerperformance"."time_tostart", "autotests_tracerperformance"."hang_atstart", "autotests_tracerperformance"."time_tohang", "autotests_tracerperformance"."hang", "autotests_tracerperformance"."crash", "autotests_tracerperformance"."stacktrace", "autotests_tracerperformance"."framemax", "autotests_tracerperformance"."maxtime", "autotests_tracerperformance"."avgtime" FROM "autotests_tracerperformance" INNER JOIN "revisions" ON ("autotests_tracerperformance"."revision_id" = "revisions"."id") WHERE ("autotests_tracerperformance"."computer_id" = 61  AND "revisions"."repo" = 'Trunk' )

直接从psql执行(最快):

2013-06-11 12:19:06 EEST psql [local] mferreiraLOG:  duration: 1332.902 ms  statement: SELECT "autotests_tracerperformance"."id", "autotests_tracerperformance"."date", "autotests_tracerperformance"."video_id", "autotests_tracerperformance"."revision_id", "autotests_tracerperformance"."computer_id", "autotests_tracerperformance"."probe", "autotests_tracerperformance"."time_tostart", "autotests_tracerperformance"."hang_atstart", "autotests_tracerperformance"."time_tohang", "autotests_tracerperformance"."hang", "autotests_tracerperformance"."crash", "autotests_tracerperformance"."stacktrace", "autotests_tracerperformance"."framemax", "autotests_tracerperformance"."maxtime", "autotests_tracerperformance"."avgtime" FROM "autotests_tracerperformance" INNER JOIN "revisions" ON ("autotests_tracerperformance"."revision_id" = "revisions"."id") WHERE ("autotests_tracerperformance"."computer_id" = 61  AND "revisions"."repo" = 'Trunk' );

其他不需要从数据库加载这么多项的查询执行的几乎相同.

为什么客户端之间存在这么大的时间差异？

注意:传输时间不相关,因为所有计算机都在同一个Intranet中.此外,当客户端请求来自运行postgresql服务器的同一台Linux机器时,会看到较慢的时间.

注意2:Psycopg2在Windows和Linux中的安装方式不同.在Windows中,我从预先打包的二进制文件安装它,在Linux中运行'pip install psycopg2',它依赖于系统上可用的postgresql安装.这会导致影响客户端性能的参数的值不同(例如'work_mem'参数)吗？

Answer 1

您可能想要检查慢速客户端是否进行SSL加密.默认情况下,它在服务器上设置并且客户端已使用SSL支持进行编译时发生.

对于检索大量数据的查询,时间差异很大.此外,某些Linux发行版(如Debian/Ubuntu)默认情况下启用SSL,即使是通过localhost进行TCP连接也是如此.

例如,这是查询检索1,5M行的时间差,这些行的总重量为64Mbytes,具有热缓存.

没有加密:

$ psql "host=localhost dbname=mlists sslmode=disable"
Password: 
psql (9.1.7, server 9.1.9)
Type "help" for help.

mlists=> \timing
Timing is on.
mlists=> \o /dev/null
mlists=> select subject from mail;
Time: 1672.258 ms

加密:

$ psql "host=localhost dbname=mlists"
Password: 
psql (9.1.7, server 9.1.9)
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)
Type "help" for help.

mlists=> \o /dev/null
mlists=> \timing
Timing is on.
mlists=> select subject from mail;
Time: 7017.935 ms

要全局关闭它,可能会SSL=off进入postgresql.conf.

要为特定范围的客户端地址关闭它pg_hba.conf,请hostnossl在更通用的host条目之前的第一个字段中添加条目.

如果关闭客户端,则取决于驱动程序如何公开sslmode连接参数.如果没有,则PGSSLMODE可以使用环境变量,如果驱动程序是在其上实现的libpq.

对于通过Unix域套接字(local)的连接,SSL从不与它们一起使用.