Database Reference
In-Depth Information
Load balancing
A balanced Cassandra cluster is the one where each node owns an equal number of keys.
This means when you query
nodetool status
, a balanced cluster will show the same
percentage for all the nodes under the
Owns
or
Effective Ownership
columns. If the
data is not uniformly distributed between the keys, even with equal ownership you will see
some nodes are more occupied by the data than others. We use
RandomPartitioner
or
Murmur3Partitioner
to avoid this sort of lopsided cluster.
Note
Note that this section is valid for a setup that does
not
use vnodes. If you are using Cas-
sandra Version 1.2 or a version after it with default settings, you can skip this section.
This section is specifically for a cluster that uses one token per Cassandra instance.
Anytime a new node is added or a node is decommissioned, the token distribution gets
skewed. Normally, one always wants Cassandra to be fairly load balanced to avoid hot-
spots. Fortunately, it is very easy to load balance. The two-step load balancing process is as
follows:
1. Calculate the initial tokens based on the partitioner that you are using. It can be
manually generated by equally dividing token range for a given partitioner among
the number of nodes.
If you are using
RandomPartitioner
, you can use
tools/bin/token-
generator
to generate tokens for you. For example, the following command
generates the tokens for two data centers; each has three nodes:
$ tools/bin/token-generator 3 3
DC #1:
Node #1: 0
Node #2: 56713727820156410577229101238628035242
Node #3: 113427455640312821154458202477256070484
DC #2:
Node #1: 169417178424467235000914166253263322299
Node #2: 55989722784154413846455963776007251813
Node #3: 112703450604310824423685065014635287055
