On 2015-07-03 19:26:05 +0200, Andres Freund wrote: > On 2015-07-03 19:02:29 +0200, Andres Freund wrote: > > Maybe I'm just daft right now (35C outside, 32 inside, so ...), but I'm > > right now missing how the whole "skip wal logging if relation has just > > been truncated" optimization can ever actually be crashsafe unless we > > use a new relfilenode (which we don't!). > > We actually used to use a different relfilenode, but optimized that > away: cab9a0656c36739f59277b34fea8ab9438395869 > > commit cab9a0656c36739f59277b34fea8ab9438395869 > Author: Tom Lane <t...@sss.pgh.pa.us> > Date: Sun Aug 23 19:23:41 2009 +0000 > > Make TRUNCATE do truncate-in-place when processing a relation that was > created > or previously truncated in the current (sub)transaction. This is safe > since > if the (sub)transaction later rolls back, we'd just discard the rel's > current > physical file anyway. This avoids unreasonable growth in the number of > transient files when a relation is repeatedly truncated. Per a > performance > gripe a couple weeks ago from Todd Cook. > > to me the reasoning here looks flawed.
It looks to me we need to re-neg on this a bit. I think we can still be more efficient than the general codepath: We can drop the old relfilenode immediately. But pg_class.relfilenode has to differ from the old after the truncation. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
