jm wrote:
Hi guys,
I want to make use of the possibylity of hot backups in 2.3. If i
understand correctly, the only thing i need to do is to open the
writers with SnapshotDeletionPolicy, is that correct?
Right.
SnapshotDeletionPolicy dp = new SnapshotDeletionPolicy(new
KeepOnlyLastCommitDeletionPolicy());
final IndexWriter writer = new IndexWriter(dir, true, new
StandardAnalyzer(), dp);
You can also wrap any other deletion policy (it doesn't have to be
KeepOnlyLastCommit).
When you want to do a backup, make sure to do try/finally, ie:
IndexCommitPoint cp = dp.snapshot();
try {
Collection files = cp.getFileNames();
<do copying here>
} finally {
dp.release();
}
And what would be the trade off of using this policy versus the
default (performance wise)? I have frenquently updating indexes (up to
tens every second) that i close periodically, and much less freqent
readers.
There should be no performance loss as far as indexing throughput goes.
Though obviously while a backup is running, if you are taxing your IO
system, then flushing/merging by the writer may take longer to run...
however, it's safe (and maybe a good idea) to throttle the IO of your
backup so you don't adversely affect ongoing indexing & searching.
It just means you hold the commit point open for longer...
There is a transient cost in disk space: while a backup is running,
the writer will not delete any segment files referenced by the commit
point you have open. So, if the writer goes and merges away some of
these segments while your backup is running, this will consume some
extra disk space. Once you release the snapshot, the disk space will
be reclaimed the next time the writer flushes, merges or is closed.
Mike
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