Re: XX000: enum value 117721 not found in cache for enum enumcrash

I wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I think the problem is that load_enum_cache_data() uses
>> GetTransactionSnapshot() rather than GetLatestSnapshot().

> That would only make the race condition window smaller (ie, hard
> to reproduce manually like this, but not gone).

No, wait, we made ALTER TYPE ADD VALUE PreventTransactionChain so that
uncommitted enum OIDs could never get into tables or indexes.  So I
think you're right, forcing a new snapshot to be used would fix this.

However, I'm a bit worried by the "if (!FirstSnapshotSet)" restriction
in GetLatestSnapshot.  Are we sure that enum comparisons could never
happen without a snapshot already being set?  What's the point of
throwing an error there anyway, as opposed to letting it redirect to
GetTransactionSnapshot?
        regards, tom lane