NEWS.txt

0.5.0
=====
0. The commitlog format has changed (but sstable format has not). 
   When upgrading from 0.4, empty the commitlog either by running 
   bin/nodeprobe flush on each machine and waiting for the flush to finish,
   or simply remove the commitlog directory if you only have test data.
   (If more writes come in after the flush command, starting 0.5 will error
   out; if that happens, just go back to 0.4 and flush again.)
   The format changed twice: from 0.4 to beta1, and from beta2 to RC1.

.5 The gossip protocol has changed, meaning 0.5 nodes cannot coexist
   in a cluster of 0.4 nodes or vice versa; you must upgrade your
   whole cluster at the same time.

1. Bootstrap, move, load balancing, and active repair have been added.
   See http://wiki.apache.org/cassandra/Operations.  When upgrading
   from 0.4, leave autobootstrap set to false for the first restart
   of your old nodes.

2. Performance improvements across the board, especially on the write
   path (over 100% improvement in stress.py throughput).

3. Configuration:
     - Added "comment" field to ColumnFamily definition.
     - Added MemtableFlushAfterMinutes, a global replacement for the 
       old per-CF FlushPeriodInMinutes setting
     - Key cache settings

4. Thrift:
     - Added get_range_slice, deprecating get_key_range


0.4.2
=====
1. Improve default garbage collector options significantly --
   throughput will be 30% higher or more.


0.4.1
=====
1. SnapshotBeforeCompaction configuration option allows snapshotting
   before each compaction, which allows rolling back to any version
   of the data.


0.4.0
=====
1. On-disk data format has changed to allow billions of keys/rows per
   node instead of only millions.  The new format is incompatible with 0.3;
   see 0.3 notes below for how to import data from a 0.3 install.

2. Cassandra now supports multiple keyspaces.  Typically you will have
   one keyspace per application, allowing applications to be able to
   create and modify ColumnFamilies at will without worrying about
   collisions with others in the same cluster.

3. Many Thrift API changes and documentation.  See 
   http://wiki.apache.org/cassandra/API

4. Removed the web interface in favor of JMX and bin/nodeprobe, which
   has significantly enhanced functionality.

5. Renamed configuration "<Table>" to "<Keyspace>".

6. Added commitlog fsync; see "<CommitLogSync>" in configuration.


0.3.0
=====
1. With enough and large enough keys in a ColumnFamily, Cassandra will
   run out of memory trying to perform compactions (data file merges).
   The size of what is stored in memory is (S + 16) * (N + M) where S
   is the size of the key (usually 2 bytes per character), N is the
   number of keys and M, is the map overhead (which can be guestimated
   at around 32 bytes per key).
   So, if you have 10-character keys and 1GB of headroom in your heap
   space for compaction, you can expect to store about 17M keys
   before running into problems.
   See https://issues.apache.org/jira/browse/CASSANDRA-208

2. Because fixing #1 requires a data file format change, 0.4 will not
   be binary-compatible with 0.3 data files.  A client-side upgrade
   can be done relatively easily with the following algorithm:
     for key in old_client.get_key_range(everything):
         columns = old_client.get_slice or get_slice_super(key, all columns)
     new_client.batch_insert or batch_insert_super(key, columns)
   The inner loop can be trivially parallelized for speed.

3. Commitlog does not fsync before reporting a write successful.
   Using blocking writes mitigates this to some degree, since all
   nodes that were part of the write quorum would have to fail
   before sync for data to be lost.
   See https://issues.apache.org/jira/browse/CASSANDRA-182

Additionally, row size (that is, all the data associated with a single
key in a given ColumnFamily) is limited by available memory, because
compaction deserializes each row before merging.

See https://issues.apache.org/jira/browse/CASSANDRA-16