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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "ArchitectureOverview" by tuxracer69
Date Sat, 14 Nov 2009 15:13:11 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=2&rev2=3

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

  At write time, 
   * you first write to a '''disk commit log''' (sequential)
   * After write to log it is sent to the appropriate nodes
-  * Each node receiving write first records it in a local log, then makes update to appropriate
'''memtables''' (one for each column family). A Memtable is Cassandra's in-memory representation
of key/value pairs
+  * Each node receiving write first records it in a local log, then makes update to appropriate
'''memtables''' (one for each column family). A Memtable is Cassandra's in-memory representation
of key/value pairs before the data gets flushed to disk as an SSTable.  
- before the data gets flushed to disk as an SSTable.  
   * '''Memtables''' are flushed to disk when:
     * Out of space
     * Too many keys (128 is default)
@@ -144, +143 @@

     * Discard tombstones
  
  
+ === Write properties ===
+ 
+  * No reads 
+  * No seeks 
+  * ''Fast''
+  * Atomic within ColumnFamily 
+  * Always writable
+ 
  
  
  
@@ -158, +165 @@

  
  
  
- Cassandra write properties
  
  
- No reads No seeks Fast Atomic within ColumnFamily Always writable
  
  
  
  
+ == Read ==
  
- 
- 
- 
- 
- == Read path ==
+ === Read path ===
  
  
+  * Any node 
+  * Partitioner 
+  * Wait for R responses 
- Any node Partitioner Wait for R responses Wait for N ­ R responses in the background and
perform read repair
+  * Wait for N -­ R responses in the background and perform read repair
  
- 
- 
- 
- 
- 
- 
- Cassandra read properties
+ === Cassandra read properties ===
  
+  * Read multiple SSTables 
+  * Slower than writes (but still fast) 
+  * Seeks can be mitigated with more RAM 
+  * Scales to billions of rows
  
- Read multiple SSTables Slower than writes (but still fast) Seeks can be mitigated with more
RAM Scales to billions of rows
  
- 
- 
- 
- 
- 
- 
- Consistency in a BASE world
+ === Consistency in a BASE world ===
  
+ Specify W, number of nodes to wait for
  
- If W + R > N, you will have consistency W=1, R=N W=N, R=1 W=Q, R=Q where Q = N / 2 +
1
+  * If W + R > N, you will have consistency 
+  * W=1, R=N 
+  * W=N, R=1 
+  * W=Q, R=Q where Q = N / 2 + 1
  
  
  
@@ -204, +204 @@

  
  
  
- vs MySQL with 50GB of data
+ Cassandra vs MySQL with 50GB of data
  
  
- MySQL
+ || MySQL       || Cassandra    ||
+ ||~300ms write || ~0.12ms write||
+ ||~350ms read  || ~15ms read   ||
  
- 
- ~300ms write ~350ms read ~0.12ms write ~15ms read
- 

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