Re: LSN as a recovery target

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Adrien Nayrat <adrien(dot)nayrat(at)dalibo(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Christoph Berg <myon(at)debian(dot)org>, Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>, Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com>
Subject: Re: LSN as a recovery target
Date: 2016-09-05 07:02:20
Message-ID: CANP8+jKSeeh8dmGhVyOqzL2N1HpBg_w5b-Rg7JJQGYAH31L9ew@mail.gmail.com
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On 5 September 2016 at 06:55, Michael Paquier <michael(dot)paquier(at)gmail(dot)com> wrote:
> On Sun, Sep 4, 2016 at 11:30 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:

>> I noticed we don't mention what LSN is anywhere, so I'd like to apply
>> the following doc patch also.
>
> +1 for the idea. What do you think about adding a mention to the
> system data type pg_lsn?
>
> <para>
> + <acronym>WAL</acronym> records are appended to the <acronym>WAL</acronym>
> + logs as each new record is written. The insert position is described by
> + a Log Sequence Number (<acronym>LSN</acronym>) that is a byte offset into
> + the logs, increasing monotonically with each new record. Two
> + <acronym>LSN</acronym>s can be compared to calculate the volume of
> + <acronym>WAL</acronym> data that separates them, so are used to measure
> + progress of <acronym>WAL</acronym> during replication and recovery.
> + </para>
> Here we could for example append a sentence like "The system data type
> <link linkend="datatype-pg-lsn"><type>pg_lsn</></link> is an internal
> representation of the LSN".

Good input, thanks. v2 attached.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Attachment Content-Type Size
doc_lsn.v2.patch application/octet-stream 1.9 KB

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