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From: Apache Wiki <wikidiffs@apache.org>
To: Apache Wiki <wikidiffs@apache.org>
Date: Mon, 23 Aug 2010 22:17:20 -0000
Message-ID: <20100823221720.42436.80776@eosnew.apache.org>
Subject: 
 =?utf-8?q?=5BCassandra_Wiki=5D_Update_of_=22Operations=22_by_RobertColi?=

Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Cassandra Wiki" for=
 change notification.

The "Operations" page has been changed by RobertColi.
The comment on this change is: removed the last reference to flushing befor=
e doing a snapshot.. also added a line clarifying that snapshot triggers th=
e flush, and what this means about what data is or isn't in the snapshot....
http://wiki.apache.org/cassandra/Operations?action=3Ddiff&rev1=3D62&rev2=3D=
63

--------------------------------------------------

  The reason why you run `nodetool cleanup` on all live nodes is to remove =
old Hinted Handoff writes stored for the dead node.
  =

  =3D=3D Backing up data =3D=3D
- Cassandra can snapshot data while online using `nodetool snapshot`.  You =
can then back up those snapshots using any desired system, although leaving=
 them where they are is probably the option that makes the most sense on la=
rge clusters.
+ Cassandra can snapshot data while online using `nodetool snapshot`.  You =
can then back up those snapshots using any desired system, although leaving=
 them where they are is probably the option that makes the most sense on la=
rge clusters. `nodetool snapshot` triggers a node-wide flush, so all data w=
ritten before the execution of the snapshot command is contained within the=
 snapshot.
  =

  With some combinations of operating system/jvm you may receive an error r=
elated to the inability to create a process during the snapshotting, such a=
s this on Linux
  =

@@ -128, +128 @@

  To revert to a snapshot, shut down the node, clear out the old commitlog =
and sstables, and move the sstables from the snapshot location to the live =
data directory.
  =

  =3D=3D=3D Consistent backups =3D=3D=3D
- You can get an eventually consistent backup by flushing all nodes and sna=
pshotting; no individual node's backup is guaranteed to be consistent but i=
f you restore from that snapshot then clients will get eventually consisten=
t behavior as usual.
+ You can get an eventually consistent backup by snapshotting all node; no =
individual node's backup is guaranteed to be consistent but if you restore =
from that snapshot then clients will get eventually consistent behavior as =
usual.
  =

  There is no such thing as a consistent view of the data in the strict sen=
se, except in the trivial case of writes with consistency level =3D ALL.
 =20