How do I delete all data in a Cassandra column family?

I'm looking for a way to delete all of the rows from a given column family in cassandra.

This is the equivalent of TRUNCATE TABLE in SQL.

You can use the truncate thrift call, or the TRUNCATE <table> command in CQL.

http://www.datastax.com/docs/1.0/references/cql/TRUNCATE

You can also do this via Cassandra CQL.

$ cqlsh
Connected to Test Cluster at localhost:9160.
[cqlsh 4.1.1 | Cassandra 2.0.6 | CQL spec 3.1.1 | Thrift protocol 19.39.0]
Use HELP for help.
cqlsh> TRUNCATE my_keyspace.my_column_family;

Its very simple in Astyanax. Just a Single Line statement

/* keyspace variable is Keyspace Type */
keyspace.truncateColumnFamily(ColumnFamilyName); 

If you are using Hector it is easy as well:

cluster.truncate("our keyspace name here", "your column family name here");

If you are using cqlsh, then you can either do it in 2 ways

1. use keyspace; and then truncate column_family;
2. truncate keyspace.column_family;

If you want to use DataStax Java driver, you can look at - http://www.datastax.com/drivers/java/1.0/com/datastax/driver/core/querybuilder/QueryBuilder.html or http://www.datastax.com/drivers/java/2.0/com/datastax/driver/core/querybuilder/Truncate.html

depending on your version.

if you are working on cluster setup, truncate can only be used when all the nodes of the cluster are UP.

By using truncate, we will miss the data(we are not sure with the importance of the data)

So the very safe way as well a trick to delete data is to use COPY command,

1. backup data using copy cassandra cmd
   copy tablename to 'path'

2. duplicate the file using linux cp cmd
   cp 'src path' 'dst path'

3. edit duplicate file in dst path, delete all lines expect first line.
   save the file.

4. use copy cassandra cmd to import
   copy tablename from 'dst path'