Re: SearchSysCache() tutorial?

> On Dec 11, 2017, at 12:40 PM, Andres Freund <andres@anarazel.de> wrote:
>
> On 2017-12-11 11:26:51 -0800, Paul Ramsey wrote:
>> On Mon, Dec 11, 2017 at 11:25 AM, Paul Ramsey <pramsey@cleverelephant.ca> wrote:
>>> Is there anywhere any documentation on SearchSysCache? I find I end up
>>> on these long spelunking expeditions through the code base for a
>>> particular problem, find the answer after many hours, then forget
>>> everything I learned because I don't exercise my knowledge frequently
>>> enough. A decent reference guide would help a lot. What do the various
>>> SysCacheIdentifier numbers mean/search, some examples, of usage, etc,
>>> etc.
>>>
>>> I can accept if there are not, but it would be a shame to keep on
>>> hunting like this if there were a good reference lying around.
>>
>> My particular hunt today is "for a given table relation, find any
>> indexes that use the gist access method and are on a single attribute
>> of type geometry".
>
> I don't think there's a way to do this with a single syscache, there
> won't be an index than can cover all of these. I'd suggest using
> RelationGetIndexList(), and then filtering for gist and attribute type
> on the returned value.

Thanks, A, I seem to be on the right path then. Loop through all indexes in RelationGetIndexList(), for those that have
arelam == GIST_AM_OID, loop through the associated columns (looks like I actually have to use a SysScanDesc on
AttributeRelationId)and look for atts that have the type I’m interested in, and if I find one, yay, we have a winner. 
Thanks,
P