Re: Online base backup from the hot-standby

2011/10/15 Jun Ishiduka <ishizuka(dot)jun(at)po(dot)ntts(dot)co(dot)jp>:
>
>> >     if (!shutdown && XLogStandbyInfoActive())
>> > +   {
>> >             LogStandbySnapshot(&checkPoint.oldestActiveXid, &checkPoint.nextXid);
>> > +           XLogReportParameters(REPORT_ON_BACKEND);
>> > +   }
>> >
>> > Why doesn't the change of FPW need to be WAL-logged when
>> > shutdown checkpoint is performed? It's helpful to add the comment
>> > explaining why.
>>
>> Sure. I update the patch soon.
>
> Done.

+ /*
+ * The backend writes WAL of FPW at checkpoint. However, The backend do
+ * not need to write WAL of FPW at checkpoint shutdown because it
+ * performs when startup finishes.
+ */
+ XLogReportParameters(REPORT_ON_BACKEND);

I'm still unclear why that WAL doesn't need to be written at shutdown
checkpoint.
Anyway, the first sentence in the above comments is not right. Not a backend but
a bgwriter writes that WAL at checkpoint.

The second also seems not to be right. It implies that a shutdown checkpoint is
performed only at end of startup. But it may be done when smart or fast shutdown
is requested.

Regards,

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