[Rt-devel] _ACLCache Clearing

[Matthew Watson]

> >  Continuing on with my struggles to get RT3 running well enough to
> > migrate to, currently looking into the caching done on the ACL
system,
> > specifically _/ACL_KEY/_CACHE in Principal_Overlay.pm ,
> >
> >
> >
> > Doing my testing on index.html , I'm confused about 2 things,
> >
> >
> >
> > Firstly, the cache doesn't really seem to kick in until the 3^rd
page
> load.
> >
> > Eg,
> >
> > 1^st page load, all unseen ACL requests must be fetched from the
> > database, any duplicate ACL requests within this page load gets a
cache
> hit,
> >
> > 2^nd  page load, same as first (same number of queries having to be
fall
> > through to the database)
> >
> > 3^rd page load, massive increase in the number of requests getting
cache
> > hits.
> >
> >
> >
> > Now, the bit I don't get it, why the 2^nd page load doesn't get the
> > increase in cache hits?
> Do you test in apache -X mode? If no then it's normal results. This
> cache is not shared between processes.


If it is not shared between processes, why does %_ACL_KEY_CACHE already
have
keys in it at the start of the 3rd page load (and subsequent page loads
provided they are within about 30 seconds of each other)?

If I add this in (at about line 300 of Principal_Overlay.pm )

#Anything older than 60 seconds needs to be rechecked
my $cache_timeout = ( time - 60 );
$RT::Logger->debug("ACL Cache Empty") unless %{$self->_ACLCache()};


The log confirms that on the 3rd page load, ACL Cache as items in it. 
Looking at the contents, it is the same at the start of the 3rd page
load, as at the end of the 2nd page load

> >
> >
> >
> > The second thing I can't work out, if I wait more than about 30
seconds
> > to reload the page, the cache seems to be empty, and we have to go
back
> > to querying the database for the ACL info. Now, it would stand to
reason
> > that I could increase the $cache_timeout value in
> > Principal_Overlay::HasRight , but that doesn't seem to effect it at
all.
> >  I guess the cache is getting cleared out somewhere else, but I
can't
> > find where.
> I don't remeber where TTL of the record is controlled, but this cache
is
> not size limited so you if you increase TTL then increase memory
usage.

I've tracked this down a bit further,but again until the 3rd page load
it seems to have problems holding onto certain records (for index.html ,
that's as far as I've got so far) it seems to be records with a
RecordCache_key like "Queues:lower(Name)=sysadmin" 

On the first and second page load, first the record tries to load it has
to
Get it from the database, second time it can get it from the cache, but
on the third page load, it can get it from the cache straight away.
Again, this seems to timeout after about 30 seconds, it then has to
fetch from the database again. I've bumped up the "cache_for_sec' value
to 600 seconds, which seems to work for other cached records, but not
for these Queues:lower(Name) ones.

Hope all this makes sense, cause I'm totally confused as to why it is
working like this. 

Regards,
Matt.




> >
> >
> >
> > Any hints on either of these would be fantastic J
> >


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