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OpenACS Home : Forums : OpenACS Improvement Proposals (TIPs) : TIP #29: [Implemented] Tree_sortkey improvements for performance and concurrency on postgresql : One Message

Forum OpenACS Improvement Proposals (TIPs): Re: TIP #29: Approved by til

Posted by Tilmann Singer on
Posted by Jeff Davis on
I made the change in a clean install and tested it for concurrency problems and with 5 simultaneous scripts creating new users I was about to create 50k users (100k acs_objects) without any duplicated keys. There were no deadlocks or any appreciable decline in the speed of account creation versus doing just one thread creating accounts (i.e. one was taking ~100ms per acct and 5 were taking ~500ms per account for about the same total accounts/sec being created).

I did find a concurrency problem with the acs_objects_context_id_up_tr trigger (which maintains the acs_object_context_index table), which only manifested itself because of a second bug in the trigger. The plain old bug was simple...it said:

  if new.object_id = old.object_id and
     new.context_id = old.context_id and
     new.security_inherit_p = old.security_inherit_p then
    return new;
  end if;
but if new.context_id and old.context_id were null it would still evaluate the trigger code since new.context_id = old.context_id is false if both are null.

Changing it to this:

if new.object_id = old.object_id
     and ((new.context_id = old.context_id)
	  or (new.context_id is null and old.context_id is null))
     and new.security_inherit_p = old.security_inherit_p then
    return new;
end if;
fixes that. Although the concurrency problem still exists, it is far less likely that it would be encountered with this fix applied.

Posted by Tom Jackson on

Thanks Jeff for doing this. This is one of those non-glamorous jobs that is probably also tedious, but I think it benefits everyone.