I normally have migrations run at server startup and depending upon the
complexity, they could run for a while if they need to do per-row data
transformations. I don't get the point regarding collisions, somebody
is going to be locked out for a while, so getting the lock for a short
period and renewing it is the same???
I used the Astyanax client for a bit but the locking recipes don't work
with CQL3 non-compact tables, when I last tried 2 months ago.
The other advantage of using CAS compared with Astyanax's lock is that
the write/read operations that Astyanax does are all done server side in
CAS, plus it avoids the issue of the hinted writes that can cause "lost"
locks.
Blair
On 06/24/2013 01:35 PM, sankalp kohli wrote:
Assuming that database migration is a one time and rare operation, why
don't you try to grab a lock for a short time. If you are able to grab
it, then you can renew it for a longer time. This will make sure that in
case of collision, all contenders wont be locked out for long time.
You can use Netflix client recipe for locks.
On Sat, Jun 22, 2013 at 3:09 PM, Blair Zajac <bl...@orcaware.com
<mailto:bl...@orcaware.com>> wrote:
Looking at the Cassandra 13 keynote [1], slide 56 regarding hinted
writes causing the lock to be taken even though the client thinks
the lock attempt failed, which the new CAS support fixes.
I have some database migrations to run on Cassandra, so I still need
a long lived lock somewhere to prevent two or more migrations
running concurrently, so CAS doesn't directly solve this problem.
It sounds like I could have a BOOLEAN column named "lock" but use
CAS to update it from false or NULL value to true and this avoids
the problem of hinted updates problem. The finally block would
reset it to false or NULL. This would be a simpler implementation
than using the wait chain algorithm.
Any problems with this?
Blair
[1]
http://www.slideshare.net/__jbellis/cassandra-summit-2013-__keynote
<http://www.slideshare.net/jbellis/cassandra-summit-2013-keynote>
[2]
http://media.fightmymonster.__com/Shared/docs/Wait%20Chain%__20Algorithm.pdf
<http://media.fightmymonster.com/Shared/docs/Wait%20Chain%20Algorithm.pdf>
