On Tue, Aug 5, 2014 at 9:04 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 5 August 2014 22:38, Claudio Freire <klaussfreire@gmail.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.
