Fatal error: Allowed memory size of 8388608 bytes exhausted
It appears that the causes vary widely, but in most of the threads I have read, nothing helped. I came across something interesting today that you might want to check out..
I was getting these error when clicking on "View Posts Since Last Visit" and sometimes while doing other things. This always occured when our PHPBB_SESSIONS table hit about 30,000 entries. Emptying this table removed the error, but also removed the new post markers so I was unable to see which posts were new - it also logs everybody out of the forums..
Today I tried something as an experiment.. I went to my /var/tmp directory on our server and deleted all of the sessions listed in there. I then tried to go back to the new posts page and got this error:
Could not delete old search id sessions
SQL Error : 1153 Got a packet bigger than 'max_allowed_packet'
DELETE FROM phpbb_search_results WHERE session_id NOT IN ('00006edd9c1212bfb9dd652d161985e5', '00053ce20283aba713c69db38c5cfc13', '00065015f0a2b90014090912fb4295f7', '000a37cebe8f1faee16f74015ba6da12', '000ae11357b551c601120787e32c66c0', '000ca40bb2a07b32a557f4dd4c2f22cf', '000d5681ec222c799dae8cfbddaebdaf'
The sessions list was thousands and thousands long... Then I found this post:
Note the response by henningl. I only made the changes to my.cnf file and everything is working much better and I also noticed a speed increase for the loading of pages.
The PHPBB_SESSIONS table is still filling up but it is no longer causing the errors. I would imagine that it will at some point, so the remaining question is - Why isn't PHPBB deleting stale sessions??? At least now I don't have to truncate this table every few hours.
Hope that helps someone, because it doesn't seem that anybody has properly answered the many incedences posted in the forums. The standard answer is to increase PHP memory to 16M in php.ini, but from what I have read, that has only helped a VERY small percentage of people. I think you might have better luck with this..