> This sounds like a really bad idea to me. A syscache based on a partial
> index is almost certainly not going to work.
>
> Before we invest in a lot of effort making bootstrap, syscache, and who
> knows what else support partial indexes, I want to see a very clear
> explanation why we must do it. Note I am looking for "*must* do it",
> not "it makes this other part of the system a little simpler".
Ok, I'm going to look into bootstrap and syscache etc. codes more to
study why "a syscache based on a partial index is almost certainly not
going to work" and how hard it would be to fix that when I have spare
time.
In the mean time I'm going to add an unique index to pg_conversion
(actually it is not so unique one. I will add the oid column to it so
that it seems "unique") and use SearchSysCacheList(). As far as I know
this is the only way to avoid heap scan every time an encoding
conversion is performed if partial index cannot be used.
Once I thought of a conversion lookup cache, but it seems impossible
to implent it since the cache needs to be invalidated when the schema
search path is changed.
--
Tatsuo Ishii