最近公司的mysql服务器经常出现阻塞状态。动不动就重启，给用户访问带来了相当的不便。
首先说明一点，每天的访问量并不大每天才2W的访问量，按道理说，访问量再增加一倍这样的服务器也应该足以承受。可是我们的服务器为什么总是这样频频重启呢？经过mysqlreport显示mysql运行的状态如下：
<PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><PRE><FONT color=#006bad>MySQL 5.1.28-rc-log uptime 0 0:4:48 Thu Apr 30 14:04:58 2009<br><br>__ Key _________________________________________________________________<BR>Buffer used 7.74M of 384.00M %Used: 2.02<BR> Current 52.89M %Usage: 13.77<BR>Write hit 0.00%<BR>Read hit 91.97%<br><br>__ Questions ___________________________________________________________<BR>Total 14.46k 50.2/s<BR> DMS 9.24k 32.1/s %Total: 63.90<BR> QC Hits 3.66k 12.7/s 25.33<BR> Com_ 1.04k 3.6/s 7.19<BR> COM_QUIT 517 1.8/s 3.58<BR> -Unknown 1 0.0/s 0.01<BR>Slow 1 s 4 0.0/s 0.03 %DMS: 0.04 Log: OFF<BR>DMS 9.24k 32.1/s 63.90<BR> SELECT 9.21k 32.0/s 63.75 99.75<BR> UPDATE 23 0.1/s 0.16 0.25<BR> REPLACE 0 0/s 0.00 0.00<BR> DELETE 0 0/s 0.00 0.00<BR> INSERT 0 0/s 0.00 0.00<BR>Com_ 1.04k 50/s 44.4<BR> set_option 523 1.8/s 3.62<BR> change_db 510 50/s 44.4<BR> show_proces 5 0.0/s 0.03<br><br>__ SELECT and Sort _____________________________________________________<BR>Scan 49 0.2/s %SELECT: 0.53<BR>Range 16 0.1/s 0.17<BR>Full join 2 0.0/s 0.02<BR>Range check 0 0/s 0.00<BR>Full rng join 0 0/s 0.00<BR>Sort scan 55 0.2/s<BR>Sort range 475 1.6/s<BR>Sort mrg pass 0 0/s<br><br>__ Query Cache _________________________________________________________<BR>Memory usage 12.02M of 150.00M %Used: 8.01<BR>Block Fragmnt 0.01%<BR>Hits 3.66k 12.7/s<BR>Inserts 9.14k 31.8/s<BR>Insrt:Prune 9.14k:1 31.8/s<BR>Hit:Insert 0.40:1<br><br>__ Table Locks _________________________________________________________<BR>Waited 0 0/s %Total: 0.00<BR>Immediate 10.49k 36.4/s<br><br>__ Tables ______________________________________________________________<BR>Open 58 of 512 %Cache: 11.33<BR>Opened 64 0.2/s<br><br>__ Connections _________________________________________________________<BR>Max used 4 of 2000 %Max: 0.20<BR>Total 519 1.8/s<br><br>__ Created Temp ________________________________________________________<BR>Disk table 1 0.0/s<BR>Table 184 0.6/s Size: 256.0M<BR>File 5 0.0/s<br><br>__ Threads _____________________________________________________________<BR>Running 2 of 2<BR>Cached 2 of 150 %Hit: 99.23<BR>Created 4 0.0/s<BR>Slow 0 0/s<br><br>__ Aborted _____________________________________________________________<BR>Clients 0 0/s<BR>Connects 0 0/s<br><br>__ Bytes _______________________________________________________________<BR>Sent 20.36M 70.7k/s<BR>Received 1.37M 4.7k/s<br><br>__ InnoDB Buffer Pool __________________________________________________<BR>Usage 304.00k of 8.00M %Used: 3.71<BR>Read hit 84.42%<BR>Pages<BR> Free 493 %Total: 96.29<BR> Data 19 3.71 %Drty: 0.00<BR> Misc 0 0.00<BR> Latched 0.00<BR>Reads 77 0.3/s<BR> From file 12 0.0/s 15.58<BR> Ahead Rnd 1 0.0/s<BR> Ahead Sql 0 0/s<BR>Writes 0 0/s<BR>Flushes 0 0/s<BR>Wait Free 0 0/s<br><br>__ InnoDB Lock _________________________________________________________<BR>Waits 0 0/s<BR>Current 0<BR>Time acquiring<BR> Total 0 ms<BR> Average 0 ms<BR> Max 0 ms<br><br>__ InnoDB Data, Pages, Rows ____________________________________________<BR>Data<BR> Reads 25 0.1/s<BR> Writes 3 0.0/s<BR> fsync 3 0.0/s<BR> Pending<BR> Reads 0<BR> Writes 0<BR> fsync 0<br><br>Pages<BR> Created 0 0/s<BR> Read 19 0.1/s<BR> Written 0 0/s<br><br>Rows<BR> Deleted 0 0/s<BR> Inserted 0 0/s<BR> Read 0 0/s<BR> Updated 0 0/s<BR>大家可以看到在Com_中占的比例是相当大的，而一般情况下，这个值应该是3.0%左右。如果这个值过高的话，就说明，你的mysql处理请求中<BR>做了一些无谓的工作，占用了大量的系统资源。其中我们看到尤为change_db的占用率比较高。这个值高了，说明我们执行的user database;命令相当多。<BR>检查程序，原来我们在执行查询语句的时候应用了mysql_query_db("database","sql");这个语句在每次执行的时候都会自动调用use database;<BR>所以我们应该将mysql_db_query 更改成mysql_query();再观察mysql的运行状态，ok。一切正常了。</FONT>
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