Understand simple mechani= cs first, decide how to act later.

=A0<= /p>

Without =96PR there=92s n= o difference from which host to run repair, it runs for the whole 100% rang= e, 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. I= t will *not* repair the whole cluster (unless the replication factor is equ= al 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, wh= ether you use -pr or not).

In general you want to use repair without -pr in case w= here 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 rel= ying on read-repair and hinted-handoff).

For repairing a whole cluster, as is the case for the w= eekly 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&= #39;t cause problems, but it does is less efficient).

--
Sylvain

=A0
=

=A0

With =96PR it runs only f= or a primary range of a node you are running a repair.=

Let say you have simple r= ing of 3 nodes with RF=3D2 and ranges (per node) N1=3DC-A, N2=3DA-B, N3=3DB= -C (node tokens are N1=3DA, N2=3DB, N3=3DC). No rack, no DC aware.

So running repair with = =96PR on node N2 will only repair a range A-B, for which node N2 is a prima= ry 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.=

=A0<= /p>

Without =96PR running on = any node will repair all ranges, A-B, B-C, C-A. A node you run a repair wit= hout =96PR is just a repair coordinator, so no difference, which one will be next time.

=A0<= /p>

=A0<= /p>

 Best regards / Pagarbiai Viktor Jevdokimov Senior Developer Phone: +370 5 212 3063, Fax +370 5 261 0453 J. Jasinskio 16C, LT-01112 Vilnius, Lithuania Follow us on Twitter: @adforminsider What is Adform: watch this short video

Disclaimer: The information contained in this message and attachments is in= tended solely for the attention and use of the named addressee and may be c= onfidential. If you are not the intended recipient, you are reminded that t= he information remains the property of the sender. You must not use, disclose, distribute, copy, print or rely= on this e-mail. If you have received this message in error, please contact= the sender immediately and irrevocably delete this message and any copies.

From: David Da= eschler [mailto:david.daeschler@gmail.com]
Sent: Tuesday, June 05, 2012 08:59
To: u= ser@cassandra.apache.org
Subject: nodetool repair -pr enough in this scenario?<= /span>

=A0

Hello,

=A0

Currently I have a 4 node cassandra cluster on CentO= S64. I have been running nodetool repair (no -pr option) on a weekly schedu= le like:

=A0

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

=A0

In this scenario, if I were to add the -pr option, w= ould this still be sufficient to prevent forgotten deletes and properly mai= ntain consistency?

=A0

Thank you,
- David

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