From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
---|---|
To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
Cc: | Gabriele Bartolini <gabriele(dot)bartolini(at)2ndquadrant(dot)it>, desmodemone <desmodemone(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Marco Nenciarini <marco(dot)nenciarini(at)2ndquadrant(dot)it>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Proposal: Incremental Backup |
Date: | 2014-08-06 01:31:51 |
Message-ID: | CAGTBQpbHhwYVKk2YZ=1chcAa4W8cBLxEYs1N1hpcr7fGX3BG9Q@mail.gmail.com |
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On Tue, Aug 5, 2014 at 9:04 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On 5 August 2014 22:38, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
>
>>> * When we take an incremental backup we need the WAL from the backup
>>> start LSN through to the backup stop LSN. We do not need the WAL
>>> between the last backup stop LSN and the new incremental start LSN.
>>> That is a huge amount of WAL in many cases and we'd like to avoid
>>> that, I would imagine. (So the space savings aren't just the delta
>>> from the main data files, we should also look at WAL savings).
>>
>> Yes, probably something along the lines of removing redundant FPW and
>> stuff like that.
>
> Not what I mean at all, sorry for confusing.
>
> Each backup has a start LSN and a stop LSN. You need all the WAL
> between those two points (-X option)
>
> But if you have an incremental backup (b2), it depends upon an earlier
> backup (b1).
>
> You don't need the WAL between b1.stop_lsn and b2.start_lsn.
>
> In typical cases, start to stop will be a few hours or less, whereas
> we'd be doing backups at most daily. Which would mean we'd only need
> to store at most 10% of the WAL files because we don't need WAL
> between backups.
I was assuming you wouldn't store that WAL. You might not even have it.
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