Latest TDB2 design and code...

ronnie sahlberg ronniesahlberg at
Sun Sep 12 01:06:43 MDT 2010

Snapshots have many more nice properties than just ctdb and ctdb recoveries.

They would allow things like
* rewind to content from previous snapshot
* (if cheap) compute delta between snapshot x and snapshot y
* compute delta between snapshot n and snapshot n-1 to allow backup or
replication of deltas.
* a series of deltas between n and n-1 allow for very compact
representation of a series of point in time backups.
* they provide an internally consistent point in time representations
if the data, which could be used for backup
or traversal purposes. traversing and/or backing the data up online
without locking database.

Cheap snapshots have almost infinite number of use cases.
I think snapshots are useful.

ronnie sahlberg

On Sun, Sep 12, 2010 at 11:52 AM,  <tridge at> wrote:
> Hi Ronnie,
>  > But I really really really would like to see
>  > cheap read-only snapshots, and cheap compute delta between two snapshots.
> why? I suspect snapshots will add a lot of complexity to the code, so
> what is the payoff for that complexity?
> I suspect you want this for inter-cluster ctdb. Perhaps instead you
> can put the snapshot support in ctdbd itself, and use a minimal set of
> hooks in tdb that allow you to record changes, similar to the locking
> hooks that Rusty is proposing.
> Cheers, Tridge

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