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.

Ivan Kartyshov
Postgres Professional: www.postgrespro.com
Russian Postgres Company

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