yet another question/issue with repair.

Cassandra 2.1.18, 3 nodes, RF=3, vnode=256, data volume ~ 5G per node only. A 
repair (nodetool repair -par) issued on a single node at this data volume takes 
around 36min with an AVG of ~ 15MByte/s disk throughput (read+write) for the 
entire time-frame, thus processing ~ 32GByte from a disk perspective so ~ 6 
times of the real data volume reported by nodetool status. Does this make any 
sense? This is with 4 compaction threads and compaction throughput = 64. 
Similar results doing this test a few times, where most/all inconsistent data 
should be already sorted out by previous runs.

I know there is e.g. reaper, but the above is a simple use case simply after a 
single failed node recovers beyond the 3h hinted handoff window. How should 
this finish in a timely manner for > 500G on a recovering node?

I have to admit this is with NFS as storage. I know, NFS might not be the best 
idea, but with the above test at ~ 5GB data volume, we see an IOPS rate at ~ 
700 at a disk latency of ~ 15ms, thus I wouldn't treat it as that bad. This all 
is using/running Cassandra on-premise (at the customer, so not hosted by us), 
so while we can make recommendations storage-wise (of course preferring local 
disks), it may and will happen that NFS is being in use then.

Why we are using -par in combination with NFS is a different story and related 
to this issue: https://issues.apache.org/jira/browse/CASSANDRA-8743. Without 
switching from sequential to parallel repair, we basically kill Cassandra.

Throughput-wise, I also don't think it is related to NFS, cause we see similar 
repair throughput values with AWS EBS (gp2, SSD based) running regular repairs 
on small-sized CFs.

Thanks for any input.
The contents of this e-mail are intended for the named addressee only. It 
contains information that may be confidential. Unless you are the named 
addressee or an authorized designee, you may not copy or use it, or disclose it 
to anyone else. If you received it in error please notify us immediately and 
then destroy it. Dynatrace Austria GmbH (registration number FN 91482h) is a 
company registered in Linz whose registered office is at 4040 Linz, Austria, 
Freist?dterstra?e 313

Reply via email to