On Tue, Jun 5, 2012 at 8:44 AM, Viktor Jevdokimov <Viktor.Jevdokimov@adform.com> wrote:

Understand simple mechanics first, decide how to act later.


Without –PR there’s no difference from which host to run repair, it runs for the whole 100% range, from start to end, the whole cluster, all nodes, at once.

That's not exactly true. A repair without -pr will repair all the ranges of the node on which repair is ran. So it will only repair the ranges that the node is a replica for. It will *not* repair the whole cluster (unless the replication factor is equal to the number of nodes in the cluster but that's a degenerate case). And hence it does matter on which host repair is run (it always matter, whether you use -pr or not).

In general you want to use repair without -pr in case where you want to repair a specific node. Typically, if a node was dead for a reasonably long time, you may want to run a repair (without -pr) on that specific node to have him catch up faster (faster that if you were only relying on read-repair and hinted-handoff).

For repairing a whole cluster, as is the case for the weekly scheduled repairs in the initial question, you want to use -rp. You *do not* want to use repair without -pr in that case. You do not because for that task using -pr is more efficient (and to be clear, not using -pr won't cause problems, but it does is less efficient).




With –PR it runs only for a primary range of a node you are running a repair.

Let say you have simple ring of 3 nodes with RF=2 and ranges (per node) N1=C-A, N2=A-B, N3=B-C (node tokens are N1=A, N2=B, N3=C). No rack, no DC aware.

So running repair with –PR on node N2 will only repair a range A-B, for which node N2 is a primary and N3 is a backup. N2 and N3 will synchronize A-B range one with other. For other ranges you need to run on other nodes.


Without –PR running on any node will repair all ranges, A-B, B-C, C-A. A node you run a repair without –PR is just a repair coordinator, so no difference, which one will be next time.



Best regards / Pagarbiai
Viktor Jevdokimov
Senior Developer

J. Jasinskio 16C, LT-01112 Vilnius, Lithuania
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From: David Daeschler [mailto:david.daeschler@gmail.com]
Sent: Tuesday, June 05, 2012 08:59
To: user@cassandra.apache.org
Subject: nodetool repair -pr enough in this scenario?




Currently I have a 4 node cassandra cluster on CentOS64. I have been running nodetool repair (no -pr option) on a weekly schedule like:


Host1: Tue, Host2: Wed, Host3: Thu, Host4: Fri


In this scenario, if I were to add the -pr option, would this still be sufficient to prevent forgotten deletes and properly maintain consistency?


Thank you,
- David