Re: incorrect handling of the timeout in pg_receivexlog

On Tue, Feb 7, 2012 at 7:06 PM, Magnus Hagander <magnus@hagander.net> wrote:
> On Tue, Feb 7, 2012 at 10:55, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com> wrote:
>> On 07.02.2012 11:35, Magnus Hagander wrote:
>>>
>>> On Tue, Feb 7, 2012 at 10:31, Heikki Linnakangas
>>> <heikki.linnakangas@enterprisedb.com>  wrote:
>>>>
>>>> So, --statusint needs to be in milliseconds. And while we're at it, how

Attached patch does that and fixes the problem caused under
--disable-integer-datetimes.

>>>>
>>>> difficult would be to ask the server for the current value of
>>>> replication_timeout, and set --statusint automatically based on that? Or
>>>> perhaps mark replication_timeout as GUC_REPORT. It is rather fiddly that
>>>> depending on a server setting, you need to pass an option in the client
>>>> or
>>>> it will just silently fail with no indication of what the problem is.
>>>
>>>
>>> We can't really ask for it easily, since we're on a replication
>>> connection. Unless we add that to the walsender grammar, but that
>>> would make it impossible to use the receivexlog stuff against a 9.1
>>> server (which I think still works, though I haven't tested it in a
>>> while).
>>
>>
>> You could put a version-check there, and only send the command if connected
>> to a 9.2 server.
>
> True..
>
>
>>> Do we have a facility to make it a GUC_REPORT but only for walsender
>>> connections?
>>
>>
>> There's no such facility at the moment.
>>
>>
>>> It seems like a very unnecessary thing to have it sent out over every
>>> single connection, since it would only be useful in a very small
>>> subset of them.
>>
>>
>> True, and conversely, many of the current GUC_REPORT settings don't apply to
>> replication clients at all. Like standard_conforming_strings and DateStyle.
>
> Right. But it's less important there, since the replication
> connections will in any reasonable configuration be only a tiny part
> of the connections.
>
>
>> I think we need another flag for settings that should be sent to replication
>> clients. GUC_REPORT_REPLICATION? Some settings would have both GUC_REPORT
>> and GUC_REPORT_REPLICATION, while others would have only one of them.
>
> Yup, seems like the cleanest solution.

Agreed. But when replication_timeout is changed by SIGHUP in the server,
there would be a delay before pg_receivexlog receives the parameter
change packet and changes the standby message interval based on the
new value of replication_timeout. Which might cause unexpected replication
timeout. So the user-settable interval (i.e., --statusint) is still useful for
people who want to avoid such fragility, even if we will support the auto-
tuning of the interval.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center