Re: repeated problems with xar_session_info table

Wow, thanks.   That's awfully thorough.
-Ryan


mikespub wrote:
> Ryan Walker wrote:
>   
>> Hi,
>>
>> I manage a site where I'm repeatedly getting the "Undefined index:  
>> xarSession_isNewSession" error.
>>
>> I can fix it each time by emptying the sessions table.  But it has now 
>> recurred three times in a few weeks.  I've never seen it occur more than 
>> once during the lifetime of any other site.
>>
>> Does anyone know what triggers this problem and why might it have 
>> occurred three times in just a few weeks?
>> Xaraya 1.1.3
>> PHP 4.4.4
>> MySQL 4.1.22
>>
>> Thanks,
>> Ryan
>>
>>     
>
> A. Where does it go wrong
> =========================
> The following happens during session initialisation in xarSession_init(),
> see file includes/xarSession.php :
>
> 1. specify how PHP should handle sessions in xarSession__setup()
>
> This tells PHP (amongst other things) to call the xarSession__phpRead()
> function whenever it wants to read session information.
>
> 2. start the actual session with session_start()
>
> Here PHP will start the session and call xarSession__phpRead() to
> try & read session information from the xar_session_info table. This
> will set $GLOBALS['xarSession_isNewSession'] to true or false depending
> on whether information is found or not.
>
> 3. if $GLOBALS['xarSession_isNewSession'] is true, call
> xarSession__new(), otherwise call xarSession__current() to
> finalise session initialisation for Xaraya
>
> This is where the error message is generated - in your case, the
> variable $GLOBALS['xarSession_isNewSession'] is not defined at all,
> because xarSession__phpRead() never gets to the point of setting
> its value :
>
>      $result =& $dbconn->Execute($query,array($sessionId));
>      if (!$result) return; // <-- yep, here's where it happens
>
>      if (!$result->EOF) {
>          $GLOBALS['xarSession_isNewSession'] = false;
>          ...
>      } else {
>          $GLOBALS['xarSession_isNewSession'] = true;
>          ...
>      }
>
> In other words, trying to select something from xar_session_info
> fails altogether, which is typical when e.g. a table is corrupted.
>
> Check the error messages you get and the MySQL error log to make
> sure that's the real cause...
>
> B. Why is this happening
> ========================
>
> The xar_session_info table is heavily loaded and gets at least one
> SELECT and two INSERTs/UPDATEs on each page hit, not to mention DELETEs
> on garbage collection.
>
> So if your site gets a lot of visitors and/or robots crawling around
> at the same time, you get a lot of read/writes on the same table, which
> isn't exactly MySQL's strong point, especially if you use the old MyISAM
> table format.
>
> C. How should I fix this
> ========================
>
> 1. Make sure your PHP/MySQL combination doesn't have a known issue with
> table corruption
>
> 2. Switch to InnoDB as table format for the xar_session_info table
>
> 3. Have a look at sessionless page caching, e.g. for your home page
>
> 4. Add a cosmetic fix in includes/xarSession.php to initialise
> $GLOBALS['xarSession_isNewSession'] before calling session_start()
>
> 5. Do a regular check/repair of your MySQL tables
>
> HTH,
>
> Mike.
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>
>   


-- 
Ryan Walker
www.WebCommunicate.net:
Insights and resources for effective websites.