Re: Hot Standby: First integrated patch

On Fri, Oct 17, 2008 at 10:38 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>
> First integrated patch for Hot Standby, allowing queries to be executed
> while in recovery mode.
>
> The patch tests successfully with the enclosed files:
> * primary_setup_test.sql - run it on primary node
> * standby_allowed.sql - run on standby - should all succeed
> * standby_disallowed.sql - run on standby - should all fail
> plus other manual testing.
>
> This is still WIP - its good enough to release for comments, though I am
> not yet confident enough to claim it bug free.
>
> What this doesn't do YET:
> * cope fully with subxid cache overflows (some parts still to add)
> * cope with prepared transactions on master
> * work correctly when running queries AND replaying WAL
> * work correctly with regard to AccessExclusiveLocks, which should
> prevent access to tables
>
> These last four points are what I'm working on over the next two weeks,
> plus any other holes people point out along the way. I have worked out
> designs for most of these aspects and will discuss them on -hackers,
> though most design notes are in the Wiki. I'm still looking into
> prepared transactions.
>
> Comments appreciated.

It appears to be working, at least in some fashion. The supplied
tests all pass.

At first glance it seems like I have to force changes to the standby
with pg_switch_xlog().

hmm.

This probably isn't right:
postgres=# \d

No relations found.
postgres=# select count(*) from foo;
count
---------
1000000
(1 row)

I created a table, pg_switch_xlog, query several times,i dropped a
table, pg_switch_xlog, table is 'gone', but still returns data

exit/enter session, now its gone. Sometimes I have to exit/enter
session to get an up to date standby. These are just first
impressions...

merlin