Re: Sync Rep v17

On Tue, 2011-03-01 at 15:25 +0900, Fujii Masao wrote:
> On Tue, Mar 1, 2011 at 9:19 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On Mon, 2011-02-28 at 18:40 +0000, Simon Riggs wrote:
> >> > SyncRepReleaseWaiters should be called when walsender exits. Otherwise,
> >> > if the standby crashes while a transaction is waiting for replication,
> >> > it waits infinitely.
> >>
> >> Will think on this.
> >
> > The behaviour seems correct to me:

> > If allow_standalone_primary = on then we sit and wait until we hit
> > client timeout, which occurs even after last standby has gone.
>
> In that case, why do backends need to wait until the timeout occurs?
> We can make those backends resume their transaction as soon as
> the last standby has gone. No?

I'm getting a little confused as to what you're asking for regarding
shutdowns and WALSender disconnects.

The current behaviour is that when a reply is received we attempt to
wake up backends waiting for an LSN. If that reply is not received
within a timeout then we just return to user anyway. You can wait
forever, if you choose, by setting the timeout to 0.

The WALSender deliberately does *not* wake waiting users if the standby
disconnects. Doing so would break the whole reason for having sync rep
in the first place. What we do is allow a potential standby to takeover
the role of sync standby, if one is available. Or the failing standby
can reconnect and then release waiters.

If we shutdown, then we wait for the shutdown commit record to be
transferred to our standby, so a normal or fast shutdown of the master
always leaves all connected standbys up to date. We already do that, so
sync rep doesn't touch that behaviour. If a standby is disconnected,
then it doesn't receive the shutdown checkpoint record.

The wait state for a commit does not persist when we shutdown and
restart.

Can you restate which bits of the above you think need to be changed?

--
Simon Riggs http://www.2ndQuadrant.com/books/
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