Re: max_worker_processes on the standby

On Wed, Jul 15, 2015 at 5:57 PM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> Fujii Masao wrote:
>> Hi,
>>
>> "25.5.3. Administrator's Overview" in the document
>> -----------------------------------------------------
>> The setting of some parameters on the standby will need reconfiguration
>> if they have been changed on the primary. For these parameters,
>> the value on the standby must be equal to or greater than the value
>> on the primary. If these parameters are not set high enough then
>> the standby will refuse to start. Higher values can then be supplied
>> and the server restarted to begin recovery again. These parameters are:
>>     max_connections
>>     max_prepared_transactions
>>     max_locks_per_transaction
>> -----------------------------------------------------
>>
>> I found that the value of max_worker_processes on the standby also
>> must be equal to or greater than the value on the master. So we should
>> just add max_worker_processes to this paragraph. Patch attached.
>
> True.  Also track_commit_timestamp.

Yes, but I intentionally did not include track_commit_timestamp in
the patch because it's not easy for me to document the hot standby
condition of track_commit_timestamp unless I read the code more.

One example which makes me a bit confusing is; both master and
standby are running fine with track_commit_timestamp disabled,
then I enable it only on the master. That is, the value of
track_commit_timestamp is not the same between master and standby.
No error happens in this case. According to the code of xlog_redo(),
the commit timestamp tracking mechanism is activated in this case.
However, after that, if standby is restarted, standby emits an error
because the value of track_commit_timestamp is not the same between
master and standby. Simple question is; why do we need to cause
the standby fail in this case? Since I'm not familiar with the code of
track_commit_timestamp yet, I'm not sure whether this behavior is
valid or not.

> Can you add a comment somewhere in
> CheckRequiredParameterValues(void) that the set of parameters is listed
> in section such-and-such in the docs, so that next time there's a higher
> chance that the docs are kept up to date?

+1

What about the attached patch?

Regards,

--
Fujii Masao