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From Robert Coli <rc...@eventbrite.com>
Subject Re: questions related to the SSTable file
Date Wed, 18 Sep 2013 01:01:45 GMT
On Tue, Sep 17, 2013 at 5:46 PM, Takenori Sato <tsato@cloudian.com> wrote:

> > So in fact, incremental backup of Cassandra is just hard link all the
> new SSTable files being generated during the incremental backup period. It
> could contain any data, not just the data being update/insert/delete in
> this period, correct?
>
> Correct.
>
> But over time, some old enough SSTable files are usually shared across
> multiple snapshots.
>

To be clear, "incremental backup" feature backs up the data being modified
in that period, because it writes only those files to the incremental
backup dir as hard links, between full snapshots.

http://www.datastax.com/docs/1.0/operations/backup_restore
"
When incremental backups are enabled (disabled by default), Cassandra
hard-links each flushed SSTable to a backups directory under the keyspace
data directory. This allows you to store backups offsite without
transferring entire snapshots. Also, incremental backups combine with
snapshots to provide a dependable, up-to-date backup mechanism.
"

What Takenori is referring to is that a full snapshot is in some ways an
"incremental backup" because it shares hard linked SSTables with other
snapshots.

=Rob

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