Ahh.. yeah. And during a compaction a new SSTable is created with the merged data.
So, if I take a snapshot before compaction, the old SSTables won't be deleted (b/c the snapshot hard links still have a reference to the files). But if I hadn't taken a snapshot before compaction, does compaction also automatically delete the old SSTables? FYI - The O'Reilly Cassandra book has a really misleading definition of snapshotting. It says that a snapshot makes a copy of the keyspace and saves it to a separate database file. Is there a way to do a read from a snapshot? So, using a client like Hector, can I request a read from a snapshot that I took like 2 weeks ago? It sounds like the main benefit of a snapshot is that it makes a bunch of nicely organized hard links in a separate folder from a specific point in time. So, taking snapshots to a different volume doesn't make sense since the hard links can't span file systems. But it would be nice to have a feature where the entire point-in-time copy of the SSTables can be copied to a different volume. Currently if the data volume gets corrupted, the snapshots on it can also get corrupted. On Wed, May 18, 2011 at 5:44 PM, Watanabe Maki <watanabe.m...@gmail.com>wrote: > SSTables are immutable. Those won't changed once written to disk. > > From iPhone > > > On 2011/05/19, at 9:37, Sameer Farooqui <cassandral...@gmail.com> wrote: > > As of 0.8.0, is it possible to take a Cassandra snapshot to a different > volume (like a EBS volume dedicated for backups)? > > About a year ago, Jonathan Ellis said that this won't be implemented b/c > snapshots are basically hard links: > <http://mail-archives.apache.org/mod_mbox/cassandra-commits/201002.mbox/%3c821546961.221891265939548009.javamail.j...@brutus.apache.org%3E> > http://mail-archives.apache.org/mod_mbox/cassandra-commits/201002.mbox/%3c821546961.221891265939548009.javamail.j...@brutus.apache.org%3E > > But I don't fully understand that. If a snapshot is just a hardlink, won't > the snapshot also change as new data is written to the SSTables? > > - Sameer > >
