Re: swapping relfilenodes (was: Re: locks in CREATE TRIGGER,

Tom Lane <tgl@sss.pgh.pa.us> writes:

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > In fact, would a truncate during a backup cause the backup to be
> > inconsistent because it wouldn't be a true snapshot of the database at
> > backup start time?  Seems so.
> 
> No, because pg_dump holds AccessShareLock on every table that it intends
> to dump, thereby ensuring that TRUNCATE/CLUSTER/etc are held off.  The
> proposal to weaken the locks that those operations take would in fact
> break pg_dump.

It seems like that would be true for TRUNCATE but not CLUSTER.

Though pg_dump works in READ COMMITTED mode doesn't it? So it doesn't really
get a consistent view of the database exactly anyways. If it tried to go in
SERIALIZABLE mode I suspect it would rarely complete though.

-- 
greg