Re: Online base backup from the hot-standby

On Mon, Oct 10, 2011 at 3:56 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> 2011/10/9 Jun Ishiduka <ishizuka(dot)jun(at)po(dot)ntts(dot)co(dot)jp>:
>
>>  Insert WAL including a value of current FPW (on master)
>>   * In the the same timing as update, they insert WAL (is named
>>     XLOG_FPW_CHANGE). XLOG_FPW_CHANGE has a value of the changed FPW.
>>   * When it creates CHECKPOINT, it adds a value of current FPW to the
>>     CHECKPOINT WAL.
>
> I can't see a reason why we would use a new WAL record for this,
> rather than modify the XLOG_PARAMETER_CHANGE record type which was
> created for a very similar reason.
> The code would be much simpler if we just extend
> XLOG_PARAMETER_CHANGE, so please can we do that?

After reading Ishiduka-san's patch, I'm thinking the opposite because
(1) Whenever full_page_writes must be WAL-logged, there is no need
to WAL-log the HS parameters. The opposite is also true. (2) How
full_page_writes record should be replayed is quite different from
how HS parameters record is.

So ISTM that the code would be simpler if we introduce new WAL
record for full_page_writes. Thought?

Regards,

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