From: | "Gokulakannan Somasundaram" <gokul007(at)gmail(dot)com> |
---|---|
To: | "Martijn van Oosterhout" <kleptog(at)svana(dot)org> |
Cc: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Index Page Split logging |
Date: | 2008-01-02 13:48:39 |
Message-ID: | 9362e74e0801020548x12c69414vfb458cead99b9589@mail.gmail.com |
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Lists: | pgsql-hackers |
On Jan 2, 2008 6:24 PM, Martijn van Oosterhout <kleptog(at)svana(dot)org> wrote:
> On Wed, Jan 02, 2008 at 04:46:11PM +0530, Gokulakannan Somasundaram wrote:
> > > All indexes are done by user-defined functions, even b-trees. People
> can
> > > make their own b-tree indexes by defining an operator class. Note that
> > > "user-defined" is this case means anything called via the fmgr
> > > interface.
> >
> > Again, i think i have one more wrong understanding. My understanding is,
> > We are discussing about user-defined functions because, they might be
> > actually be mutable functions, but the user might have classified as
> > immutable.
>
> This is where it gets a bit beyond by depth, so someone may have to
> correct me. The point is that during the recovery the system is not yet
> fully running and not everything works yet. For example, what happens
> if the system crashed halfway through updating a page in pg_proc and
> that page needs to be recovered from WAL. Yet to insert into the index
> you need to be able to read pg_am, pg_amproc, pg_proc at least,
> probably more.
>
> The point being, you can't rely on anything except WAL during recovery.
>
> Thanks a lot for the nice explanation. That was something new for
me....:((
--
Thanks,
Gokul.
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