Cassandra Data Modeling - Beginning Apache Cassandra Development - page 53

Cassandra-powered applications (e.g., Number of page hits, number of active users,
etc.).
In Cassandra, a counter is a 64-bit signed integer. A write on counter will require a
read from replica nodes (this depends on consistency level, default is ONE). While
reading a counter column value, read has to be consistent.

Counter Column with and without replicate_on_write

Default value of replicate_on_write is true. If set to false it will replicate on one rep-
lica node (irrespective of replication factor). That might be helpful to avoid read-
before-write on serving write request. But any subsequent read may not be consistent
and may also result in data loss (single replica node is gone!).

Play with Counter Columns

In Chapter 1 we discussed setting multiple clusters on a single machine. First let's start
with a cluster of three nodes on a single machine. (Please refer to the “Configuring
Multiple Nodes on a Single Machine” section in Chapter 1 .) In this recipe we will dis-
cuss the do's and don'ts of using counter columns.

1. Let's create a keyspace counterkeyspace :

create keyspace counterkeyspace with
replication = {'class' : 'SimpleStrategy',
'replication_factor' : 2 }

2. Create a column family counternoreptable with replic-

ate_on_write as false :

create table counternoreptable(id text
PRIMARY KEY, pagecount counter) with
replicate_on_write='false';

3. Update pagecount to increment by 2 as follows:

update counternoreptable set
pagecount=pagecount+2 where id = '1';