Re: Changeset Extraction v7.9.1

Hi,

On 2014-03-05 23:20:57 +0100, Andres Freund wrote:
> On 2014-03-05 17:05:24 -0500, Robert Haas wrote:
> > > I very much dislike having the three different event loops, but it's
> > > pretty much forced by the design of the xlogreader. "My" xlogreader
> > > version didn't block when it neeeded to wait for WAL but just returned
> > > "need input/output", but with the eventually committed version you're
> > > pretty much forced to block inside the read_page callback.
> > >
> > > I don't really have a idea how we could sensibly unify them atm.
> >
> > WalSndLoop(void (*gutsfn)())?
>
> The problem is that they are actually different. In the WalSndLoop we're
> also maintaining the walsender's state, in WalSndWriteData() we're just
> waiting for writes to be flushed, in WalSndWaitForWal we're primarily
> waiting for the flush pointer to pass some LSN. And the timing of the
> individual checks isn't trivial (just added some more comments about
> it).
>
> I'll simplify it by pulling out more common code, maybe it'll become
> apparent how it should look.

I've attached a new version of the walsender patch. It's been rebased
ontop of Heikki's latest commit to walsender.c. I've changed a fair bit
of stuff:
* The sleeptime is now computed to sleep until we either need to send a
keepalive or kill ourselves, as Heikki sugggested.
* Sleep time computation, sending pings, checking timeouts is now done
in separate functions.
* Comment and codestyle improvements.

Although they are shorter and simpler now, I have not managed to unify
the three loops however. They seem to be too different to unify them
inside one. I tried a common function with an 'wait_for' bitmask
argument, but that turned out to be fairly illegible. The checks in
WalSndWaitForWal() and WalSndLoop() just seem to be too different.

I'd be grateful if you (or somebody else!) could have a quick look at
body of the loops in WalSndWriteData(), WalSndWaitForWal() and
WalSndLoop(). Maybe I am just staring at it the wrong way.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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