- As part of the cache-saving feature, a third directory
(along with data and commitlog) has been added to the config
file. You will need to set and create this directory
when restarting your node into 0.6.6.
- We try to keep minor versions 100% compatible (data format,
commitlog format, network format) within the major series, but
we introduced a network-level incompatibility in 0.6.1.
Thus, if you are upgrading from 0.6.0 to any higher version
(0.6.1, 0.6.2, etc.) then you will need to restart your entire
cluster with the new version, instead of being able to do a
- row caching: configure with the RowsCached attribute in
- Hadoop map/reduce support: see contrib/word_count for an example
- experimental authentication support, described under
Authenticator in storage.conf
- MemtableSizeInMB has been replaced by MemtableThroughputInMB which
triggers a memtable flush when the specified amount of data has
been written, including overwrites.
- MemtableObjectCountInMillions has been replaced by the
MemtableOperationsInMillions directive which causes a memtable flush
to occur after the specified number of operations.
- Like MemtableSizeInMB, BinaryMemtableSizeInMB has been replaced by
- Replication factor is now per-keyspace, rather than global.
- KeysCachedFraction is deprecated in favor of KeysCached
- RowWarningThresholdInMB added, to warn before very large rows
get big enough to threaten node stability
- removed deprecated get_key_range method
- added batch_mutate meethod
- deprecated multiget and batch_insert methods in favor of
multiget_slice and batch_mutate, respectively
- added ConsistencyLevel.ANY, for when you want write
availability even when it may not be readable immediately.
Unlike CL.ZERO, though, it will throw an exception if
it cannot be written *somewhere*.
- read and write statistics are reported as lifetime totals,
instead of averages over the last minute. average-since-last
requested are also available for convenience.
- cache hit rate statistics are now available from JMX under
- compaction JMX metrics are moved to
org.apache.cassandra.db.CompactionManager. PendingTasks is now
a much better estimate of compactions remaining, and the
progress of the current compaction has been added.
- commitlog JMX metrics are moved to org.apache.cassandra.db.Commitlog
- progress of data streaming during bootstrap, loadbalance, or other
data migration, is available under
See http://wiki.apache.org/cassandra/Streaming for details.
- 0.6 network traffic is not compatible with earlier versions. You
will need to shut down all your nodes at once, upgrade, then restart.
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).
- Added "comment" field to ColumnFamily definition.
- Added MemtableFlushAfterMinutes, a global replacement for the
old per-CF FlushPeriodInMinutes setting
- Key cache settings
- Added get_range_slice, deprecating get_key_range
1. Improve default garbage collector options significantly --
throughput will be 30% higher or more.
1. SnapshotBeforeCompaction configuration option allows snapshotting
before each compaction, which allows rolling back to any version
of the data.
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
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.
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.
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.
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.