From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Paul Caskey <paul(at)nmxs(dot)com> |
Cc: | Chris Bitmead <chrisb(at)nimrod(dot)itg(dot)telstra(dot)com(dot)au>, Postgres Users <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: 4 billion record limit? |
Date: | 2000-07-25 22:03:26 |
Message-ID: | 8266.964562606@sss.pgh.pa.us |
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Lists: | pgsql-general pgsql-novice |
Paul Caskey <paul(at)nmxs(dot)com> writes:
> Tom Lane wrote:
>> It's only a hard limit if your application assumes OIDs are unique.
>> If you don't assume that, then I think it's not a big problem.
>>
>> It's possible (though obviously not especially likely) that you might
>> get OID collisions in the system tables after an OID-counter wraparound.
> This implies they do wrap around. So they are reused? Chris said no, but
> you're saying yes.
> (Maybe they wrap around "by accident", by adding one to MAXINT, which will
> give zero on an unsigned int, I believe. Will the system choke on zero?
> Has anyone tested this wraparound?)
Yes, yes, and yes ;-). I just committed a patch to prevent the system
from generating a zero OID during wraparound. I think that the old code
would not have done so in any case, but correct behavior would've
depended on the stored OID counter always being a multiple of 32,
which seems a tad risky to assume over a long time span. There's a
more direct check for wraparound in there now.
(No, I didn't test it the hard way ... just stopped the postmaster and
hacked on the OID counter in the pg_variable file by hand ...)
> Even if they do wrap, if I have some old records lying around with a low
> OIDs, they will trip me up.
No doubt about it, you're likely to get a few "duplicate key" errors and
stuff like that. I'm just observing that it's not likely to be a
complete catastrophe, especially not if you don't rely on OIDs to be
unique in your user tables.
We have talked about offering 8-byte OIDs as a compile-time option,
and I think it'll happen eventually, but I'm not holding my breath.
Lots of other stuff seems more pressing...
regards, tom lane
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