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From "Jeremiah Jordan" <JEREMIAH.JOR...@morningstar.com>
Subject RE: Node repair questions
Date Mon, 11 Jul 2011 21:21:30 GMT
The more often you repair, the quicker it will be.  The more often your
nodes go down the longer it will be.

Repair streams data that is missing between nodes.  So the more data
that is different the longer it will take.  Your workload is impacted
because the node has to scan the data it has to be able to compare with
other nodes, and if there are differences, it has to send/receive data
from other nodes.


-----Original Message-----
From: A J [mailto:s5alye@gmail.com] 
Sent: Monday, July 11, 2011 2:43 PM
To: user@cassandra.apache.org
Subject: Node repair questions

Hello,
Have the following questions related to nodetool repair:
1. I know that Nodetool Repair Interval has to be less than
GCGraceSeconds. How do I come up with an exact value of GCGraceSeconds
and 'Nodetool Repair Interval'. What factors would want me to change the
default of 10 days of GCGraceSeconds. Similarly what factors would want
me to keep Nodetool Repair Interval to be just slightly less than
GCGraceSeconds (say a day less).

2. Does a Nodetool Repair block any reads and writes on the node, while
the repair is going on ? During repair, if I try to do an insert, will
the insert wait for repair to complete first ?

3. I read that repair can impact your workload as it causes additional
disk and cpu activity. But any details of the impact mechanism and any
ballpark on how much the read/write performance deteriorates ?

Thanks.

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