Latest TDB2 design and code...

tridge at tridge at
Sun Sep 12 05:24:00 MDT 2010

Hi Ronnie,

 > 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.

yes, these are all basic properties of snapshots, but the question
still stands - what will Samba use them for?

How will users benefit from us having snapshots?

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

I love them in filesystems, but I also know just how much complexity
they add and just how much they can affect performance and prevent

I can see how they could be used in ctdb when you have wide area
clusters. That is a pretty esoteric use case for something that will
have a major impact on the code.

So what is another use case that would make it worthwhile to add this
to tdb?

Cheers, Tridge

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