Re: Transaction Snapshots and Hot Standby

On Fri, 2008-09-12 at 13:53 +0300, Hannu Krosing wrote:

> 4. Slave keeps copies of removed pages or rows when WAL apply removes
> old versions .
> 
> Possible ways to do this
> 
>  * inside Slave - have some backup store tied to OldestXmin intervals
> 
>   * variant 1 - have one global store, accessed through shared mem
>   * variant 2 - present removed pages to interested backends and 
>                 let them (decide to) keep them 
> 
>  * outside Slave - having file system keep old snapshots as long as
> needed, still must tie to OldestXmin intervals, but most of work done by
> storage layer (SAN or overlay file system).

Possible options for "outside Slave" filesystem snapshooting - 

ZFS ( http://en.wikipedia.org/wiki/ZFS ) is very likely usable 

Linux LVM + XFS may be usable -
http://arstechnica.com/articles/columns/linux/linux-20041013.ars

Possibly also http://en.wikipedia.org/wiki/Btrfs .

----------------
Hannu