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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "ArchitectureInternals" by JonathanEllis
Date Thu, 08 Apr 2010 15:41:52 GMT
Dear Wiki user,

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The "ArchitectureInternals" page has been changed by JonathanEllis.


   * !StorageProxy gets the nodes responsible for replicas of the keys from the !ReplicationStrategy,
then sends read messages to them
     * This may be a !SliceFromReadCommand, a !SliceByNamesReadCommand, or a !RangeSliceReadCommand,
   * On the data node, !ReadVerbHandler gets the data from CFS.getColumnFamily or CFS.getRangeSlice
and sends it back as a !ReadResponse
+    * The row is located by doing a binary search on the index in SSTableReader.getPosition
     * For single-row requests, we use a !QueryFilter subclass to pick the data from the Memtable
and SSTables that we are looking for.  The Memtable read is straightforward.  The SSTable
read is a little different depending on which kind of request it is:
       * If we are reading a slice of columns, we use the row-level column index to find where
to start reading, and deserialize block-at-a-time (where "block" is the group of columns covered
by a single index entry) so we can handle the "reversed" case without reading vast amounts
into memory
       * If we are reading a group of columns by name, we still use the column index to locate
each column, but first we check the row-level bloom filter to see if we need to do anything
at all

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