multithreading - CPU usage of Java + JDBC -

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while testing webapp under load got following top excerpt under linux:

 pid user      pr  ni  virt  res  shr s %cpu %mem    time+  command 3964 nobody    20   0 4965m 622m 6048 s  8.5 11.0   6:02.49 java  1985 mysql     20   0  294m 125m 3804 s  2.1  2.2   0:05.39 /usr/sbin/mysqld

i need explanation on java's %cpu column. understand it, during web request 1 of java's thread performing pure java logic, consuming of cpu time (let 5ms). connects database via jdbc, sends sql query , waits, 10ms, response. these 10ms counted /usr/sbin/mysqld cpu usage. java thread resumes it's operation , finishes, consuming 20ms , amounting 5+10+20=30ms total execution time.

and newbie question is: don't think these db-related 10ms counted twice: 1 time java thread waiting db process query , second time database cpu usage itself? don't understand here?

when process waiting on socket not using significant amounts of cpu. basically, kernel knows in waiting state , not schedule run - except little things signal handling, can used e.g. run garbage collector regularly.

(ok, if there lot of garbage collect, "little thing" might not little.)


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