> - we are running on production linux VMs (not ideal but this is out of our > hands) Is the VM doing anything wacky with the IO ?
> As part of a DR exercise, we killed all 6 nodes in DC1, Nice disaster. Out of interest, what was the shutdown process ? > We noticed that data that was written an hour before the exercise, around the > last memtables being flushed,was not found in DC1. To confirm, data was written to DC 1 at CL LOCAL_QUORUM before the DR exercise. Was the missing data written before or after the memtable flush ? I'm trying to understand if the data should have been in the commit log or the memtables. Can you provide some more info on how you are detecting it is not found in DC 1? > If we understand correctly, commit logs are being written first and then to > disk every 10s. Writes are put into a bounded queue and processed as fast as the IO can keep up. Every 10s a sync messages is added to the queue. Not that the commit log segment may rotate at any time which requires a sync. A loss of data across all nodes in a DC seems odd. If you can provide some more information we may be able to help. Cheers ----------------- Aaron Morton Freelance Developer @aaronmorton http://www.thelastpickle.com On 24/08/2012, at 6:01 AM, rubbish me <rubbish...@googlemail.com> wrote: > Hi all > > First off, let's introduce the setup. > > - 6 x C* 1.1.2 in active DC (DC1), another 6 in another (DC2) > - keyspace's RF=3 in each DC > - Hector as client. > - client talks only to DC1 unless DC1 can't serve the request. In which case > talks only to DC2 > - commit log was periodically sync with the default setting of 10s. > - consistency policy = LOCAL QUORUM for both read and write. > - we are running on production linux VMs (not ideal but this is out of our > hands) > ----- > As part of a DR exercise, we killed all 6 nodes in DC1, hector starts talking > to DC2, all the data was still there, everything continued to work perfectly. > > Then we brought all nodes, one by one, in DC1 up. We saw a message saying all > the commit logs were replayed. No errors reported. We didn't run repair at > this time. > > We noticed that data that was written an hour before the exercise, around the > last memtables being flushed,was not found in DC1. > > If we understand correctly, commit logs are being written first and then to > disk every 10s. At worst we lost the last 10s of data. What could be the > cause of this behaviour? > > With the blessing of C* we could recovered all these data from DC2. But we > would like to understand why. > > Many thanks in advanced. > > Amy > >
