[Rt-devel] Why are Groups cachedmembers of themselves?

[Joby Walker]

Jesse,

I've pushed the below changes to our dev system and purged the duplicate 
cachedgroupmember records -- we haven't come across a problem yet. 
Doing so dropped the size of the cachedgroupmember table by more than 
2/3!  In our production system (currently) this will mean a drop of 65% 
(833,989 records to 288,706).

Joby Walker
C&C SSG, University of Washington


Joby Walker wrote:
> Jesse Vincent wrote:
>>> So why is this necessary?  Is it for ACL checks on User Defined groups?
>>
>> It's for ~all group ACL and groupmember checks.
>>
> 
> Ok, it took me a while to see where the cachedgroupmember record is 
> necessary: When you make a check to see if a group has the ACL to do X 
> (exactly what you said).
> 
> The impact of adding hundreds of thousands of additional records seems 
> like a very high cost to be able to do these group queries just like 
> user permission queries.
> 
> I grabbed a fresh rt-3.4.4 (what we currently use) and Modified the 
> following:
> 
> RT::Group_Overlay->_Create()
> 
> comment out line 511,512 where the group is added as a cached member of 
> itself.
> 
> RT::Principal_Overlay->HasRight()
> 
> Add on line 401 (just before the "Build that honkin-big SQL query") a 
> check that if the Principal is a Group to determine if that group has a 
> specific ACL.
> 
>     if ($self->IsGroup) {
>     my $qb = 'SELECT ACL.id from ACL, Principals WHERE'
>             ." ( ACL.RightName = 'SuperUser' OR ACL.RightName = '$right' 
> ) "
>         ."AND Principals.Disabled = 0 "
>         ."AND Principals.id = " . $self->Id . " "
>         ."AND Principals.id = ACL.principalid "
>         ."AND ( " . join( ' OR ', @look_at_objects ). ") ";
>         $self->_Handle->ApplyLimits( \$qb, 1 );
>         my $hitcount = $self->_Handle->FetchResult($qb);
>     if ($hitcount) {
>             return (1);
>         }
>     }
> 
> 
> With these two changes all of the regression tests pass.
> 
> Joby Walker
> C&C SSG, University of Washington
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