Re: 64-bit XIDs again

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: 64-bit XIDs again
Date: 2015-08-01 00:27:22
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Josh Berkus <josh(at)agliodbs(dot)com> writes:
> On 07/31/2015 02:46 PM, Heikki Linnakangas wrote:
>> Well, sure, if you don't want the clog to grow arbitrarily large, then
>> you need to freeze. And most people would want to freeze regularly, to
>> keep the clog size in check. The point is that you wouldn't *have* to do
>> so at any particular time. You would never be up against the wall, in
>> the "you must freeze now or your database will shut down" situation.

> Well, we still have to freeze *eventually*. Just not for 122,000 years
> at current real transaction rates. In 2025, though, we'll be having
> this conversation again because of people doing 100 billion transactions
> per second. ;-)

Well, we'd wrap the 64-bit WAL position counters well before we wrap
64-bit TIDs ... and there is no code to support wraparound in WAL LSNs.

regards, tom lane

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