Re: [BUGS] BUG #14825: enum type: unsafe use?

On 09/23/2017 06:06 PM, Tom Lane wrote:
> Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> writes:
>> OK, I think I'm convinced. Here's is the WIP code I put together for the
>> blacklist. I'm was looking for a place to put the init call, but since
>> it's possibly not going anywhere I stopped :-) . My initial thought
>> about substransactions was that we should ignore them for this purpose
>> (That's why I used TopTransactionContext for the table).
> For the blacklist, I agree we could just ignore subtransactions: all
> subtransaction levels are equally uncommitted for this purpose, and
> leaving entries from failed subtransactions in place seems like a
> non-issue, since they'd never be referenced again. (Well, barring OID
> wraparound and an enum-value-OID collision while the transaction runs,
> but I think we can ignore that as having probability epsilon.)
>
> But you need to actually put the table in TopTransactionContext, not
> CurTransactionContext ;-). Also, I don't think you need an init call
> so much as an end-of-transaction cleanup call. Maybe call it
> AtEOXactEnum(), for consistency with other functions called in the
> same area.
>
>> w.r.t. table size - how large? I confess I haven't seen any systems with
>> more than a few hundred enum types. But even a million or two shouldn't
>> consume a huge amount of memory, should it?
> Dynahash tables are self-expanding, so I don't see a need to stress about
> that too much. Anything in 10-100 seems reasonable for initial size.
>

OK, here's the finished patch. It has a pretty small footprint all
things considered, and I think it guarantees that nothing that could be
done in this area in 9.6 will be forbidden. That's probably enough to
get us to 10 without having to revert the whole thing, ISTM, and we can
leave any further refinement to the next release.

cheers

andrew

--
Andrew Dunstan https://www.2ndQuadrant.com
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