From: | Kartyshov Ivan <i(dot)kartyshov(at)postgrespro(dot)ru> |
---|---|
To: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
Cc: | PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: proposal: get oldest LSN - function |
Date: | 2016-03-11 13:35:08 |
Message-ID: | 56E2C98C.7030502@postgrespro.ru |
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Lists: | pgsql-hackers |
On 11.03.2016 16:33, Kartyshov Ivan wrote:
>
>
> On 28.02.2016 11:36, Michael Paquier wrote:
>> On Sun, Feb 28, 2016 at 4:40 PM, Kartyshov Ivan wrote:
>>> It will not satisfy our purposes and our administrators for three
>>> reasons.
>>> 1) DBA set me task to get the oldest number that present in WAL, not
>>> last
>> Yeah I got that.
>>
>>> 2) Surely we can choose the oldest segment from list
>>> "pg_ls_dir('pg_xlog')"
>>> of segments and calculate the first LSN by hand, but it is not what
>>> we want
>>> to do manually.
>> That's where I am not following. In any case you are just one SQL
>> query away from the result. And actually your patch is incorrect I
>> think. If you care about the oldest record available you should look
>> for the first LSN position of the oldest segment, no? What you are
>> calculating now is the oldest virtual LSN position in local pg_xlog.
>
> Sorry, for long not answering and thank you for time you spent
> reviewing this patch, please clarify what you meen, when you say
> "virtual LSN position".
> In whole you are right, my main goal is to get the oldest LSN position
> in local pg_xlog, and i agree with you that it isn`t too hard to get
> it by SQL query. But it will be more usefull, to have easy access in
> userspace.
>
>
You wrote "If you care about the oldest record available you should look
for the first LSN position of the oldest segment, no?"
Yes I do it exactly this way.
--
--
Ivan Kartyshov
Postgres Professional: www.postgrespro.com
Russian Postgres Company
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