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Start background writer during archive recovery. Background writer now performs

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its usual buffer cleaning duties during archive recovery, and it's responsible
for performing restartpoints.

This requires some changes in postmaster. When the startup process has done
all the initialization and is ready to start WAL redo, it signals the
postmaster to launch the background writer. The postmaster is signaled again
when the point in recovery is reached where we know that the database is in
consistent state. Postmaster isn't interested in that at the moment, but
that's the point where we could let other backends in to perform read-only
queries. The postmaster is signaled third time when the recovery has ended,
so that postmaster knows that it's safe to start accepting connections.

The startup process now traps SIGTERM, and performs a "clean" shutdown. If
you do a fast shutdown during recovery, a shutdown restartpoint is performed,
like a shutdown checkpoint, and postmaster kills the processes cleanly. You
still have to continue the recovery at next startup, though.

Currently, the background writer is only launched during archive recovery.
We could launch it during crash recovery as well, but it seems better to keep
that codepath as simple as possible, for the sake of robustness. And it
couldn't do any restartpoints during crash recovery anyway, so it wouldn't be
that useful.

log_restartpoints is gone. Use log_checkpoints instead. This is yet to be
documented.

This whole operation is a pre-requisite for Hot Standby, but has some value of
its own whether the hot standby patch makes 8.4 or not.

Simon Riggs, with lots of modifications by me.
This commit is contained in:
Heikki Linnakangas
2009-02-18 15:58:41 +00:00
parent 36a9cf38c5
commit cdd46c7654
8 changed files with 920 additions and 191 deletions
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7
src/backend/storage/buffer/README
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@ -1,4 +1,4 @@
$PostgreSQL: pgsql/src/backend/storage/buffer/README,v 1.15 2008/11/06 20:51:14 tgl Exp $
$PostgreSQL: pgsql/src/backend/storage/buffer/README,v 1.16 2009/02/18 15:58:41 heikki Exp $
Notes About Shared Buffer Access Rules
======================================
@ -268,3 +268,8 @@ out (and anyone else who flushes buffer contents to disk must do so too).
This ensures that the page image transferred to disk is reasonably consistent.
We might miss a hint-bit update or two but that isn't a problem, for the same
reasons mentioned under buffer access rules.
As of 8.4, background writer starts during recovery mode when there is
some form of potentially extended recovery to perform. It performs an
identical service to normal processing, except that checkpoints it
writes are technically restartpoints.