mysqlreport显示Com_中change_db占用比例高的问题的解决方法
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
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：MySQL 5.1.28-rc-log uptime 0 0:4:48 Thu Apr 30 14:04:58 2009__ Key _________________________________________________________________Buffer used 7.74M of 384.00M %Used: 2.02 Current 52.89M %Usage: 13.77Write hit 0.00%Read hit 91.97%__ Questions ___________________________________________________________Total 14.46k 50.2/s DMS 9.24k 32.1/s %Total: 63.90 QC Hits 3.66k 12.7/s 25.33 Com_ 1.04k 3.6/s 7.19 COM_QUIT 517 1.8/s 3.58 -Unknown 1 0.0/s 0.01Slow 1 s 4 0.0/s 0.03 %DMS: 0.04 Log: OFFDMS 9.24k 32.1/s 63.90 SELECT 9.21k 32.0/s 63.75 99.75 UPDATE 23 0.1/s 0.16 0.25 REPLACE 0 0/s 0.00 0.00 DELETE 0 0/s 0.00 0.00 INSERT 0 0/s 0.00 0.00Com_ 1.04k 50/s 44.4 set_option 523 1.8/s 3.62 change_db 510 50/s 44.4 show_proces 5 0.0/s 0.03__ SELECT and Sort _____________________________________________________Scan 49 0.2/s %SELECT: 0.53Range 16 0.1/s 0.17Full join 2 0.0/s 0.02Range check 0 0/s 0.00Full rng join 0 0/s 0.00Sort scan 55 0.2/sSort range 475 1.6/sSort mrg pass 0 0/s__ Query Cache _________________________________________________________Memory usage 12.02M of 150.00M %Used: 8.01Block Fragmnt 0.01%Hits 3.66k 12.7/sInserts 9.14k 31.8/sInsrt:Prune 9.14k:1 31.8/sHit:Insert 0.40:1__ Table Locks _________________________________________________________Waited 0 0/s %Total: 0.00Immediate 10.49k 36.4/s__ Tables ______________________________________________________________Open 58 of 512 %Cache: 11.33Opened 64 0.2/s__ Connections _________________________________________________________Max used 4 of 2000 %Max: 0.20Total 519 1.8/s__ Created Temp ________________________________________________________Disk table 1 0.0/sTable 184 0.6/s Size: 256.0MFile 5 0.0/s__ Threads _____________________________________________________________Running 2 of 2Cached 2 of 150 %Hit: 99.23Created 4 0.0/sSlow 0 0/s__ Aborted _____________________________________________________________Clients 0 0/sConnects 0 0/s__ Bytes _______________________________________________________________Sent 20.36M 70.7k/sReceived 1.37M 4.7k/s__ InnoDB Buffer Pool __________________________________________________Usage 304.00k of 8.00M %Used: 3.71Read hit 84.42%Pages Free 493 %Total: 96.29 Data 19 3.71 %Drty: 0.00 Misc 0 0.00 Latched 0.00Reads 77 0.3/s From file 12 0.0/s 15.58 Ahead Rnd 1 0.0/s Ahead Sql 0 0/sWrites 0 0/sFlushes 0 0/sWait Free 0 0/s__ InnoDB Lock _________________________________________________________Waits 0 0/sCurrent 0Time acquiring Total 0 ms Average 0 ms Max 0 ms__ InnoDB Data, Pages, Rows ____________________________________________Data Reads 25 0.1/s Writes 3 0.0/s fsync 3 0.0/s Pending Reads 0 Writes 0 fsync 0Pages Created 0 0/s Read 19 0.1/s Written 0 0/sRows Deleted 0 0/s Inserted 0 0/s Read 0 0/s Updated 0 0/s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。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;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。
