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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "FAQ" by MakiWatanabe
Date Fri, 22 Apr 2011 12:07:49 GMT
Dear Wiki user,

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

The "FAQ" page has been changed by MakiWatanabe.
The comment on this change is: Add #seed and #seed_spof.


   * [[#replicaplacement|How does Cassandra decide which nodes have what data?]]
   * [[#cachehitrateunits|I have a row or key cache hit rate of 0.XX123456789.  Is that XX%
or 0.XX% ?]]
   * [[#bigcommitlog|Commit Log gets very big. Cassandra does not delete "old" commit logs.
+  * [[#seed|What are seeds?]]
+  * [[#seed_spof|Does single seed mean single point of failure?]]
@@ -431, +434 @@

  update column family XXX with memtable_flush_after=60;
+ <<Anchor(seed)>>
+ == What are seeds? ==
+ Seeds, or seed nodes are the nodes which new nodes refer to on
+ bootstrap to know ring information.
+ When you add a new node to ring, you need to specify at least one live
+ seed to contact. Once a node join the ring, it learns about the other
+ nodes, so it doesn't need seed on subsequent boot.
+ There is no special configuration for seed node itself. In stable and
+ static ring, you can point non-seed node as seed on bootstrap though
+ it is not recommended.
+ Nodes in the ring tend to send Gossip message to seeds more often ( Refer to [[ArchitectureGossip]]
for more
+ details ) than to non-seeds. In other words, seeds are worked as hubs of Gossip network.
+ With seeds, each node can detect status changes of other nodes quickly.
+ <<Anchor(seed_spof)>>
+ == Does single seed mean single point of failure? ==
+ If you are using replicated CF on the ring, only one seed in the ring
+ doesn't mean single point of failure. The ring can operate or boot
+ without the seed. However, it will need more time to spread status changes of node over
the ring.
+ It is recommended to have multiple seeds in production system.

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