Re: [HACKERS] tables > 1 gig

> > > Unlinking unused segments after truncating to zero length may cause
> > > the result such as
> > >
> > > Existent backends write to the truncated file to extend
> > the relation
> > > while new backends create a new segment file to extend the
> > relation.
> >
> > How about my idea of creating a truncated file, the renaming it to the
> > table file. That keeps the table open for other open file descriptors,
> > but put a zero-length file in place in an atomic manner.
> >
>
> Sorry,I couldn't understand what you mean.
> What is differenct from truncating existent files to zero length ?

Glad to explain. Here is the pseudocode:

create temp file, make it zero length, call it 'zz'
rename(zz,tablename)

What this does is to create a zero length file, and the rename unlinks
the tablename file, and puts the zero-length file in it's place.
rename() is atomic, so there is no time that the table file does not
exist.

It allows backends that have the table open via a descriptor to keep the
table unchanged, while new backends see a zero-length file.

Does this help?

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