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From Manuel Vacelet <manuel.vace...@gmail.com>
Subject [users@httpd] Re: mod_ldap cache and strace doesn't tell the same story
Date Wed, 17 Mar 2010 15:16:44 GMT
On Tue, Mar 16, 2010 at 2:18 PM, Manuel Vacelet
<manuel.vacelet@gmail.com> wrote:
> On Tue, Mar 16, 2010 at 11:06 AM, Manuel Vacelet
> <manuel.vacelet@gmail.com> wrote:
>> Hi all,
>>
>> I'm facing a strange issue.
>> I have a major performance penalty on some apache related operations
>> (svn checkout that used to take 5mn but that suddenly takes more than
>> 7 hours).
>>
>> I'm running a standard RHEL5.3 with apache 2.2.3 (fyi the server runs
>> mod_php, mod_auth_mysql and some other modules too).
>>
>> Thanks to strace, I identified that the httpd process that is "very
>> long" (the httpd process that discuss with svn client that takes hour
>> to complete).
>> The process makes a lot of operation on a file descriptor attached to
>> my ldap server and is regulary blocking with following syscall:
>> poll([{fd=3, events=POLLIN|POLLPRI|POLLERR|POLLHUP}], 1, -1 <unfinished ...>
>>
>> fd3 is a socket (/proc/<pid>/fd/3) and the inode of this socket is
>> used to communicate with the ldap server (shown by netstat)
>>
>> This is where I no longer understand what happens:
>> - I'm using mod_ldap so there should be a cache of all ldap info.
>> - ldap-status confirm that the credentials used for the svn operation
>> are in cache.
>> - The cache is far from full (2%)
>> - The hit ratio is close to 100%
>>
>> => Why there is an activity between my httpd process and the ldap server ?
>
> I think I have an answer to this question:
> In some cases, the apache process (I'm running prefork) doesn't use
> mod_ldap cache.
>
> I made a test:
> In parallel of a very slow checkout, I ran another one. The second
> checkout was running as normal rate.
> A couple of strace on the server later, it appears that, the apache
> process that server the second checkout never talk to the ldap server
>
> So the new question is:
> Why 2 apache processes forked from the same root could behave so differently ?

Does anybody have an explanation to this whole thing ?

Why "sometimes" mod_ldap never cache my credentials ?
Or in other words: "what would make mod_ldap not to cache users credentials" ?

Manuel

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