meike.talbach@xxxxxxxxxxxxxxxxx writes:
> When I query this through pgsql, the queries are fast as expected.
> select * from push_topic where guid = 'DD748CCD-B8A4-3B9F-8F60-67F1F673CFE5'
> Index Scan using push_topic_idx_topicguid on push_topic (cost=0.42..8.44 rows=1 width=103) (actual time=0.117..0.121 rows=1 loops=1)
> Index Cond: ((guid)::bpchar = 'DD748CCD-B8A4-3B9F-8F60-67F1F673CFE5'::bpchar)
> Buffers: shared hit=3 read=1
> Total runtime: 0.191 ms
> However when I run the exact query through a different application (CodeSynthesis ORM) the query is very slow (~ 115ms logged)
> I noted this is due to a sequential scan happening on the table instead of an index scan.
It looks like what that app is actually issuing is something different
from what you tested by hand, to wit
select * from push_topic where guid = 'DD748CCD-B8A4-3B9F-8F60-67F1F673CFE5'::text
which causes the comparison to be resolved as texteq not bpchareq, ie you
effectively have
select * from push_topic where guid::text = 'DD748CCD-B8A4-3B9F-8F60-67F1F673CFE5'::text
and that doesn't match a bpchar index. If you can't persuade the app to
label the comparison value as bpchar not text, the easiest fix would be
to create an additional index on "guid::text".
Or, better, persuade the app to label the value "
public.push_guid" since that is the column's type...a type you haven't defined for us. If you get to add explicit casts this should be easy...but I'm not familiar with the framework you are using.
David J.
