Re: Infrastructure changes for recovery

Simon Riggs wrote:

> I propose to
> * have startup process signal postmaster when it starts Redo phase (if
> it starts it)

I think the first is a good idea -- at least, if you can get the startup
process to use the normal ReadBuffer code path instead of
XLogReadBuffer. I don't really know what's needed for this to work, but
there seem to be several layers of stuff that need to be up for this to
work.

> * have startup process signal postmaster again when it has completed
> recovery, so that the change of state is via explicit signal rather than
> death of the child process

I'm not sure that this is very useful, because the startup process
cannot do anything much. It is an auxiliary process, which means it
can't connect to a database and it can't run transactions.

This other idea:

> ii) have postmaster allow connections while Redo is taking place, as one
> part of allowing query access to standby database

is interesting and I'm sure it would be very welcome. Of course, it is
first necessary to be able to run transactions in true "read only" mode,
which perhaps is nowadays not so difficult given the work with VXids.

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support