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Re: Advice on MyXactMade* flags, MyLastRecPtr, pendingDeletes and lazy XID assignment

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Florian G(dot) Pflug" <fgp(at)phlo(dot)org>
Cc: Postgresql-Hackers <pgsql-hackers(at)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: Re: Advice on MyXactMade* flags, MyLastRecPtr, pendingDeletes and lazy XID assignment
Date: 2007-08-30 04:33:03
Message-ID: 16736.1188448383@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> And I'm quite tempted to not flush the XLOG at all during ABORT, and to
> only force synchronous commits if one of the to-be-deleted files is
> non-temporary.

+1 on the first, but -1 on the second, because we'd have to track
whether deleted files are temp or not ... it's very unclear that it'd
be worth the trouble.

> OTOH, it'd allow aynchronous commits for transactions that created
> temporary tables.

It'd be for xacts that *dropped* temp tables, no?  I'm not sure that
is a performance-critical path --- probably it more usually gets done
after the client's already disconnected.

>> The only way we could make this more robust is if we could have
>> WAL-before-data rule for file *creation*, but I think that's not
>> possible given that we don't know what relfilenode number we will use
>> until we've successfully created a file.

> It seems doable, but it's not pretty. One possible scheme would be to
> emit a record *after* chosing a name but *before* creating the file,

No, because the way you know the name is good is a successful
open(O_CREAT).

			regards, tom lane

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