On Sat, Apr 9, 2011 at 7:03 AM, Bruce Momjian <bruce@momjian.us> wrote:
> Bruce Momjian wrote:
>> Alvaro Herrera wrote:
>> >
>> > Why is it important to have the original pg_clog files around? Since
>> > the transactions in question are below the freeze horizon, surely the
>> > tuples that involve those transaction have all been visited by vacuum
>> > and thus removed if they were leftover from aborted transactions or
>> > deleted, no? So you could just fill those files with the 0x55 pattern
>> > (signalling "all transactions are committed") and the net result should
>> > be the same. No?
>> >
>> > Forgive me if I'm missing something. I haven't been following this
>> > thread and I'm more than a little tired (but wanted to shoot this today
>> > because I'm gonna be able to, until Monday).
>
> To answer your other question, it is true we _probably_ could assume all
> the rows were committed, except that again, vacuum might not have run
> and the pages might not be full so single-page cleanup wasn't done
> either.
OK, continuing the thought of just making all the old clog files as
"all committed"...
Since it only affects "toast" tables, the only time the system (with
normal queries) would check for a particular toast tuple, the tuple
referring to it would have been committed, right? So forcing "all
transactions committed" for the older clog segments might mean a scan
on a *toast* heap might return tuples as committed when they might
have been aborted, but the real table heap would never refer to those,
right?
a.
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