Re: Add statistics to pg_stat_wal view for wal related parameter tuning

On 2020-11-13 12:32, lchch1990@sina.cn wrote:
>> Now, pg_stat_wal supports reset all informantion in WalStats
>> using pg_stat_reset_shared('wal') function.
>> Isn't it enough?
> Yes it ok, sorry I miss this infomation.

OK.

>>> 3. I do not think it's a correct describe in document for
>>> 'wal_buffers_full'.
> 
>> Where should I rewrite the description? If my understanding is not
>> correct, please let me know.
> Sorry I have not described it clearly, because I can not understand
> the meaning of this
> column after I read the describe in document.
> And now I read the source code of walwrite and found the place where
> 'wal_buffers_full'
> added is for a backend to wait a wal buffer which is occupied by other
> wal page, so the
> backend flush the old page in the wal buffer(after wait it can).
> So i think the origin decribe in document is not so in point, we can
> describe it such as
> 'Total number of times WAL data written to the disk because a backend
> yelled a wal buffer
> for an advanced wal page.
> 
> Sorry if my understand is wrong.

Thanks for your comments.

You're understanding is almost the same as mine.
It describes when not only backends but also other backgrounds 
initialize a new wal page,
wal buffer's space is already used and there is no space.

> 'Total number of times WAL data written to the disk because a backend
> yelled a wal buffer for an advanced wal page'

Thanks for your suggestion.
I wondered that users may confuse about how to use "wal_buffers_full" 
and how to tune parameters.

I thought the reason which wal buffer has no space is
important for users to tune the wal_buffers parameter.

How about the following comments?

'Total number of times WAL data was written to the disk because WAL 
buffers got full
  when to initialize a new WAL page'


Regards,
-- 
Masahiro Ikeda
NTT DATA CORPORATION