Re: Getting rid of wal_level=archive and default to hot_standby + wal_senders

On Tue, Feb 3, 2015 at 1:43 PM, Andres Freund <andres(at)2ndquadrant(dot)com>
wrote:

> Hi,
>
> I think these days there's no reason for the split between the archive
> and hot_standby wal levels. The split was made out of volume and
> stability concerns. I think we can by now be confident about the
> wal_level = hot_standby changes (note I'm not proposing hot_standby =
> on).
>
> So let's remove the split. It just gives users choice between two options
> that don't have a meaningful difference.
>

+1.

Additionally I think we should change the default for wal_level to
> hot_standby and max_wal_senders (maybe to 5). That way users can use
> pg_basebackup and setup streaming standbys without having to restart the
> primary. I think that'd be a important step in making setup easier.
>

Yes, please!

Those who want to optimize their WAL size can set it back to minimal, but
let's make the default the one that makes life *easy* for people.

The other option, which would be more complicated (I have a semi-finished
patch that I never got time to clean up) would be for pg_basebackup to be
able to dynamically raise the value of wal_level during it's run. It would
not help with the streaming standby part, but it would help with
pg_basebackup. That could be useful independent - for those who prefer
using wal_level=minimal and also pg_basebackup..

Previously there have been arguments against changing the default of
> wal_level because it'd mean the regression tests wouldn't exercise
> minimal anymore. That might be true, but then right now we just don't
> exercise the more complex levels. If we're really concerned we can just
> force a different value during the tests, just as we do for prepared
> xacts.
>

Seems we should focus our tests on the stuff that people actually use in
reality? :) And if we change the default, then even more people will use
that level.

But it would definitely be a good idea to have some buildfarm animals set
up to test each one.

Comments?
>
> Additionally, more complex and further into the future, I wonder if we
> couldn't also get rid of wal_level = logical by automatically switching
> to it whenever logical slots are active.
>

If it can be safely done online, I definitely think that would be a good
goal to have. If we could do the same for hot_standby if you had physical
slots, that might also be a good idea?

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/