Re: [PROPOSAL] Shared Ispell dictionaries

On Sun, Mar 25, 2018 at 02:28:29PM -0400, Tom Lane wrote:
> Arthur Zakirov <a(dot)zakirov(at)postgrespro(dot)ru> writes:
> > If all dictionaries will be shareable then this view could be removed.
> > Unfortunately I think it can't help with leaked segments, I didn't find
> > a way to iterate dshash entries. That's why pg_ts_shared_dictionaries()
> > scans pg_ts_dict table instead of scanning dshash table.
>
> If you're scanning pg_ts_dict, what happens with dictionaries belonging
> to other databases? They won't be visible in your local copy of
> pg_ts_dict. Between that and the inability to find leaked segments,
> I'm not seeing that this has much use-case.

Indeed pg_ts_dict scanning is wrong way here. And
pg_ts_shared_dictionaries() is definitely broken.

> > Yes unfortunately ALTER TEXT SEARCH DICTIONARY doesn't reload a
> > dictionary. TID can help here. I thought about using XID too when I
> > started to work on RELOAD command. But I'm not sure that it is a good
> > idea, anyway XID isn't needed in current version.
>
> Actually, existing practice is to check both xmin and tid; see for example
> where plpgsql checks if a cached function data structure still matches the
> pg_proc row, pl_comp.c around line 175 in HEAD. The other PLs do it
> similarly I think. I'm not sure offhand just how much that changes the
> risks of a false match compared to testing only one of these fields, but
> I'd recommend conforming to the way it's done elsewhere.

Thank you for pointing to it! I think it shouldn't be hard to use both
xmin and tid.

--
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company