Cron jobs fail, all connected functionality (search, other modules) ceases to work

Hi,

this problem is a bit strange, and I'm not sure if the Watchdog module is the the final and definite cause of it, but I was pointed to it by some module's maintainers. In the following, I'm assuming that stuff like admin/logs/status/run-cron is a part of the Watchdog module; if not, I might be in the wrong place. I'm giving it a "normal" priority, since most Drupal sites appear not to be affected, but to those where it appears, it is critical in regard to system maintenance, and core functionality. I'm suspecting that somehow the Watchdog module might have a memory leak; if someone who has better knowledge about Drupal's internals can determine that this can not be the case, please accept my apologies and close this bug, or move it to an appropriate thread.

Short description:

* On one of my sites, Drupal's Cron tasks fail without exception; they can't be successfully started manually (via /admin/logs/status/run-cron), nor via cron.php. The logged error messages usually follow pretty much the same pattern: "Fatal error: Allowed memory size of xxx bytes"; they point to several installed modules. Usually, I can raise the memory limit in php.ini, and/or disable the referenced module. On the next Cron run, the mentioned error will be there again and reference another module. I'm playing this game for over a month, and currently the most basic thing appearing not to work is /admin/logs/status/run-cron resp. the default Cron job itself. Since Cron jobs don't run, all functionality connected to it breaks (e.g. Search module, and other 3rd party modules like Amazontools or the great admin/logs/updates).

Additional Information which might be helpful:

* Cron has been configured according to http://drupal.org/node/23714 (wget version)

* I'm running five different sites under Drupal 5.2; the mentioned error eppears only in one of these sites, which is the largest and oldest Drupal installation I'm currently running (since 2005/Drupal 4.x; > 20.000 nodes). I'm pretty sure, that the problem is caused by something in Drupal core, since several different modules result in the same error; also I'm suspecting, the the error message is misleading or not accurate; e.g. it reads "134217728 bytes exhausted (tried to allocate 1486766"; imho this means, that 134 MB are available, and 1,4 MB are unsuccessfully are requested - how can this be? (which also could be a bug in Watchdog module).

* System configuration: I'm running Drupal 5.2 with MySQL 5.0.32, PHP 5.2.0-8+etch7, and Apache/2.2.3 on Debian GNU/Linux 4.0 (Etch).

* In php.ini, I started with a memory limit of 8 MB which I increased in the last four weeks to 16, 32, 64, and currently 128 MB. Cron jobs still fail, but with 128 MB memory limit, search module seems to have started indexing 20k+ nodes (which I don't understand, since the Cron jobs fail, but anyway). However, requiring 128 MB to even index a bunch of nodes appears not healthy to me (the server has 2 GB of RAM).

Error messages:

* admin/logs/watchdog is recording entries like "Cron-Lauf hat die Zeitbegrenzung überschritten und wurde abgebrochen" (= Cron run has exceeded time limit and was cancelled)

* Manually running admin/logs/status/run-cron results in messages like "Cron run failed" or "Cron runs for over one hour and has probably crashed", or (currently, just as an example): "Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 1486766 bytes) in /var/www/drupal/modules/notify/notify.module on line 437"

Detailed descriptions:

* Firstly I traced the error to 3rd party modules like Amazontools; for a description see http://drupal.org/node/160743. Since this module seems to be unmaintained in the last few months, nobody with a better knowledge looked into the error. Amazontools is a "usual suspect" since it has grave bugs and relies heavily on Cron updates. I tried to disable the module, but this led to the same error, referencing a different module.

* An example for another module is the Sitedoc module, which is very actively maintained; the current status is, that the error appears in connection with Sitedoc, but is unlikely to be caused by the Sitedoc module; see http://drupal.org/node/161314.

That's all that currently comes into mind. Any suggestions or ideas?

Thanks & greetings, -asb