| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Andrew Dunstan <andrew(at)dunslane(dot)net>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: WIP: extensible enums |
| Date: | 2010-10-24 04:04:03 |
| Message-ID: | AANLkTi=VnQV+XhRDSR9WyRyUZCXSrVdC3CTRCzyt6Ag=@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sat, Oct 23, 2010 at 8:11 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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