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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "ArchitectureOverview" by tuxracer69
Date Mon, 16 Nov 2009 19:08:19 GMT
Dear Wiki user,

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

The "ArchitectureOverview" page has been changed by tuxracer69.
http://wiki.apache.org/cassandra/ArchitectureOverview?action=diff&rev1=4&rev2=5

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

  Information is mainly based on [[http://assets.en.oreilly.com/1/event/27/Cassandra_%20Open%20Source%20Bigtable%20+%20Dynamo%20Presentation.pdf|J
Ellis OSCON 09 presentation ]]
  
  
- == Motivation ==
  
  
- Scaling reads to a relational database is hard Scaling writes to a relational database is
virtually impossible
  
- 
- ... and when you do, it usually isn't relational anymore
  
  Why Cassandra
   * MySQL drives too many random I/Os
@@ -83, +79 @@

  
  
  
- 
+ == Keys distribution and Partition ==
  Dynamo architecture & Lookup
+ 
+ 
+ In a ring of nodes A, B, C, D, E, F and G
+ Nodes B, C and D store keys in the range (''a'',''b'') including key ''k''
+ 
+ 
+ You can decide where the key should go in Cassandra using the {{{IntitialToken}}} parameter
for your {{{Partitioner}}}, see [[StorageConfiguration|Storage Configuration]]
  
  Architecture details
  
@@ -200, +203 @@

  write replica count > replication factor).
  
  
- 
+ You get consistency if R + W > N, where R is the number of records to read, W is the
number of records to write, and N is the replication factor.  A ConsistencyLevel of ONE means
R or W is 1.  A ConsistencyLevel of QUORUM means R or W is ceiling((N+1)/2).  A ConsistencyLevel
of ALL means R or W is N.  So if you want to write with a ConsistencyLevel of ONE and then
get the same data when you read, you need to read with ConsistencyLevel ALL.
  
  Cassandra vs MySQL with 50GB of data
  

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