Re: Re: [COMMITTERS] pgsql: Make a hard state change from catchup to streaming mode.

On Fri, Feb 18, 2011 at 11:50 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Feb 18, 2011 at 10:41 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> On Fri, Feb 18, 2011 at 10:09 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>>> Make a hard state change from catchup to streaming mode.
>>>> More useful state change for monitoring purposes, plus a
>>>> required change for synchronous replication patch.
>>
>>> As far as I can see, this patch was not posted or discussed before
>>> commit, and I'm not sure it's the behavior everyone wants.  It has the
>>> effect of preventing the system from ever going backwards from
>>> "streaming" to "catchup".  Is that what we want?
>>
>> That seems like a very bad idea from here.  Being able to go back to
>> catchup after loss of the streaming connection is essential for
>> robustness.  If we now have to restart the slave for that to happen,
>> it's not an improvement.
>
> No, that's not the case where it matters.  The state would get reset
> on reconnect.  The problem is when, say, the master server is
> generating WAL at a rate which exceeds the network bandwidth of the
> link between the master and the standby.  The previous coding will
> make us flip back into the catchup state when that happens.
>
> Actually, the old code is awfully sensitive, and knowing that you are
> not caught up is not really enough information: you need to know how
> far behind you are, and how long you've been behind for.  I'm guessing
> that Simon intended this patch to deal with that problem, but it's not
> the right fix.

So am I the only one who thinks this needs to be reverted?

--
Robert Haas
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