Re: About to add WAL write/fsync statistics to pg_stat_wal view

On 2021/03/22 16:50, Fujii Masao wrote:
> 
> 
> On 2021/03/22 9:50, ikedamsh wrote:
>> Agreed. I separated the patches.
>>
>> If only the former is committed, my trivial concern is that there may be
>> a disadvantage, but no advantage for the standby server. It may lead to
>> performance degradation to the wal receiver by calling
>> INSTR_TIME_SET_CURRENT(), but the stats can't visible for users until the
>> latter patch is committed.
> 
> Your concern is valid, so let's polish and commit also the 0003 patch to v14.
> I'm still thinking that it's better to separate wal_xxx columns into
> walreceiver's and the others. But if we count even walreceiver activity on
> the existing columns, regarding 0003 patch, we need to update the document?
> For example, "Number of times WAL buffers were written out to disk via
> XLogWrite request." should be "Number of times WAL buffers were written
> out to disk via XLogWrite request and by WAL receiver process."? Maybe
> we need to append some descriptions about this into "WAL configuration"
> section?

Agreed. Users can know whether the stats is for walreceiver or not. The
pg_stat_wal view in standby server shows for the walreceiver, and in primary
server it shows for the others. So, I updated the document.
(v20-0003-Makes-the-wal-receiver-report-WAL-statistics.patch)

>> I followed the argument of pg_pwrite().
>> But, I think "char *" is better, so fixed it.
> 
> Thanks for updating the patch!
> 
> +extern int    XLogWriteFile(int fd, char *buf,
> +                          size_t nbyte, off_t offset,
> +                          TimeLineID timelineid, XLogSegNo segno,
> +                          bool write_all);
> 
> write_all seems not to be necessary. You added this flag for walreceiver,
> I guess. But even without the argument, walreceiver seems to work expectedly.
> So, what about the attached patch? I applied some cosmetic changes to the patch.

Thanks a lot. Yes, "write_all" is unnecessary.
Your patch is looks good to me.


Regards,
-- 
Masahiro Ikeda
NTT DATA CORPORATION