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Re: Unlogged tables cannot be truncated twice

From: Andres Freund <andres(at)anarazel(dot)de>
To: pgsql-bugs(at)postgresql(dot)org
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>, Greg Sabino Mullane <greg(at)endpoint(dot)com>
Subject: Re: Unlogged tables cannot be truncated twice
Date: 2011-05-31 07:44:25
Message-ID: 201105310944.26712.andres@anarazel.de (view raw or flat)
Thread:
Lists: pgsql-bugs
On Tuesday, May 31, 2011 03:27:22 Alvaro Herrera wrote:
> Excerpts from Andres Freund's message of lun may 30 20:47:49 -0400 2011:
> > On Tuesday, May 31, 2011 02:35:58 AM Andres Freund wrote:
> > > On Tuesday, May 31, 2011 02:14:00 AM Andres Freund wrote:
> > > > On Tuesday, May 31, 2011 01:56:05 AM Cédric Villemain wrote:
> > > > > I remove my own explanations as we conclude on the same thing.
> > > > > Attached is the fix by adding a (!reindex)  in the index.c if().
> > > > 
> > > > Thats imo wrong because it will break a plain REINDEX?
> > > 
> > > > I think one possible correct fix would be the attached:
> > > My version was wrong as well because it  did not observe
> > > RelationTruncate's nblocks argument. That function is used to
> > > "shorten" the relation in vacuum. So dropping the init fork there is
> > > not a good idea.
> > > 
> > > So I think it is the simpler version of simply checking the existance
> > > of the fork before creating is ok.
> 
> Hmm, I wonder if what we should be doing here is observe isreindex in
> index_build to avoid creating the init fork.  Doing smgr access at that
> level seems wrong.
isreindex doesn't contain the necessary informormation as its set doing a 
REINDEX even though a new relfilenode is created and thus the fork needs to be 
created.

It doesn't seem terribly clean do do the !smgrexists(), I aggree with you 
there. On the other hand we are calling smgrcreate() two lines down anyway. I 
personally don't realy like the placement of that piece of code very much. 
Doing it in index_build seems to be the wrong place. I don't think there 
really is a good place for it right now.

Andres

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