Re: WIP: extensible enums

Robert Haas <robertmhaas@gmail.com>

From: Robert Haas <robertmhaas@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Andrew Dunstan <andrew@dunslane.net>, Dean Rasheed <dean.a.rasheed@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>

Date: 2010-10-24T04:04:03Z

Lists: pgsql-hackers

On Sat, Oct 23, 2010 at 8:11 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> Why would you need to lock out type comparisons?
>
> Didn't you get the point?  The hazard is to a concurrent process that is
> merely trying to load up its enum-values cache so that it can perform an
> enum comparison.  I don't want such an operation to have to block,
> especially not against something that's trying to acquire a more or less
> exclusive lock.

Hmm, yeah, I missed the point.  Sorry.

I suppose you could fix this by always updating every row, and storing
in each row the total count of elements (or a random number).  Then
it'd be obvious if you'd read an inconsistent view of the world.

-- 
Robert Haas
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