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Performed strace on one one of the apache children and its showing 24 seconds between two system calls.How can i determine what is the cause of this behavior.It looks like both children are taking almost same amound of time(24.7 and 23.92) seconds.

we are using apache prefork with php5 and mysql 5

/var/lib/php5/ is the php session folder

strace output of apache children1 with processid -20539

ps -u www-data | grep apache2 | awk '{print"-p " $1}' | xargs strace -o /strace/strace.log -ff -s4096 -r

20539 0.000064 close(13) = 0

20539 0.000060 open("/var/lib/php5/sess_9t2cvnvdoruh666rjpm515idm0", O_RDWR|O_CREAT, 0600) = 13

20539 0.000065 flock(13, LOCK_EX) = 0

20539 24.711888 fcntl(13, F_SETFD, FD_CLOEXEC) = 0

20539 0.000056 fstat(13, {st_mode=S_IFREG|0600, st_size=211, ...}) = 0

20539 0.000080 lseek(13, 0, SEEK_SET) = 0

strace output of apache children2 with processid - 20556

20556 0.000056 close(13) = 0

20556 0.000058 open("/var/lib/php5/sess_9t2cvnvdoruh666rjpm515idm0", O_RDWR|O_CREAT, 0600) = 13

20556 0.000062 flock(13, LOCK_EX) = 0

20556 23.928294 fcntl(13, F_SETFD, FD_CLOEXEC) = 0

20556 0.000055 fstat(13, {st_mode=S_IFREG|0600, st_size=211, ...}) = 0

20556 0.000083 lseek(13, 0, SEEK_SET) = 0

Can it be a problem with file that file descriptor(13) called?? is there anything wrong with my understanding of strace output.

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1 Answer 1

up vote 4 down vote accepted

On the process take a look at the lsof -p <pid>

Notably you're looking for FD 13

i.e. from one of my httpd deployments.

httpd 10865 apache 13w REG 8,5 1113187 59310687 /var/log/httpd/some_site.log

I'd look at contention with obtaining an exclusive lock on the file, noted in FD 13 in this case, if other processes are contending for locks, as noted by fcntl then this would explain your long wait.

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1  
Thank you for reminding me about lsof, i forgot to check that.Thanks –  ananthan Jul 10 '12 at 15:56
    
@user113505 great; if this solves your issue please remember to click the accept tick :) –  Oneiroi Jul 10 '12 at 16:02
    
sure i will :-) –  ananthan Jul 10 '12 at 16:07

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