Hello,
Full snapshot forces a flush, yes.
Incremental hard-links to SSTables, yes.
This question really depends on how your cluster was "lost".
Node Loss: You would be able to restore a node based on restoring
backups + commit log or just by using repair.
Cluster Loss: (all nodes down scenario with recoverable machines/disks):
You would be able to restore to the point where you captured your last
incremental backup. If you had a commit log, then those operations would
be replayed during bootstrapping. You would also have to restore SSTables
that were written to disk but not captured in an incremental backup.
Cluster Loss: (all nodes down scenario with unrecoverable
machines/disks): You would only be able to restore to the last incremental
backup point. This assumes you save backups off Cluster.
The commit log's goal is to provide durability in case of node failure
prior to a flush operation. The commit log will be replayed during
bootstrapping a node and will repopulate memtables. There is also a commit
log archive and restore feature as well:
http://www.datastax.com/documentation/cassandra/2.0/cassandra/configuration/configLogArchive_t.html.
I have not personally used this feature so cannot comment on it's
performance/stability.
Does this help?
BTW: Here's the 1.2 documentation for backup and restore -
http://www.datastax.com/documentation/cassandra/1.2/cassandra/operations/ops_backup_restore_c.html
Here's the 2.0 documentation for backup and restore -
http://www.datastax.com/documentation/cassandra/2.0/cassandra/operations/ops_backup_restore_c.html
Thanks,
Jonathan
Jonathan Lacefield
Solutions Architect, DataStax
(404) 822 3487
<http://www.linkedin.com/in/jlacefield>
<http://www.datastax.com/what-we-offer/products-services/training/virtual-training>
On Thu, Mar 6, 2014 at 9:14 AM, java8964 <java8...@hotmail.com> wrote:
> Hi,
>
> Currently I am looking how the bacup/restore be done in Cassandra, based
> the document from DataStax:
>
> http://www.datastax.com/docs/1.1/backup_restore
>
> Here is one way to do it:
>
> 1) Do a full snapshot every week
> 2) Enable incremental backup every day
>
> So with last snapshot + the incremental backups after that snapshot, you
> can restore the cluster to the stage before it is lost.
>
> Here are my understanding how Cassandra will flush from Memtable to
> SSTable files in snapshot or incremental backups:
>
> 1) Full snapshot will force Cassandra flush all memtables to SSTable
> files, but incremental backup won't.
> 2) Incremental backup just hard-link all the SSTables after the last
> snapshot.
>
> Here is my question:
>
> If the my above understanding is correct, let's say there is a data change
> happened after the last snapshot, then recorded into commit log, and stored
> in memtable, but never flush to the SSTables yet, at this time, we lost our
> cluster. Will that change be lost just based on last snapshot plus
> incremental backups? Or besides the last snapshot plus incremental backups,
> we also need all commit log for a restore?
>
> Thanks
>
> Yong
>
