From: | Masahiro Ikeda <ikedamsh(at)oss(dot)nttdata(dot)com> |
---|---|
To: | lchch1990(at)sina(dot)cn |
Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Add statistics to pg_stat_wal view for wal related parameter tuning |
Date: | 2020-11-16 09:24:10 |
Message-ID: | 3599412d5f3eee44e3658e81d3790f6a@oss.nttdata.com |
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Thread: | |
Lists: | pgsql-hackers |
On 2020-11-13 12:32, lchch1990(at)sina(dot)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
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