Taking a Global Snapshot of Cassandra Clusters

Procedure

Run the nodetool snapshot command, specifying the hostname, JMX port, and keyspace. For example:

$ nodetool -h localhost -p 7199 snapshot mykeyspace

Results

The snapshot is created in the data_directory_location/keyspace_name/table_name–UUID/snapshots/snapshot_name directory. Each snapshot directory contains numerous .db files that contain the data at the time of the snapshot. Such as:

Package Installations

/var/lib/cassandra/data/mykeyspace/users-081a1500136111e482d09318a3b15cc2/snapshots/1406227071618/mykeyspace-users-ka-1-Data.db

Tarball Installations

install_location/data/data/mykeyspace/users-081a1500136111e482d09318a3b15cc2/snapshots/1406227071618/mykeyspace-users-ka-1-Data.db

Taking a Global Snapshot

As stated earlier, a global snapshot can be taken using the pssh tool. So let us configure this tool first.

The steps for configuring the pssh are:

1. Install the pssh tool using the following command

   sudo apt-get install python-pip
   sudo pip install pssh

2. Create a hosts file that contains all the ip’s of the nodes present in that cluster and name it something like pssh-hosts.
   
   It should look something like this:

   192.168.2.123
   192.168.2.125
   192.168.2.120

3. Now run the following command so that the snapshots get created on each and every node:

    pssh -h pssh-hosts -P "/root/cassandra/bin/nodetool -h localhost -p 7199 snapshot "

Now you've taken the dump of data on each node. You can download it using secure copy and restore it accordingly. I am still working on automating the process of downloading the dump, but I will update you all  as soon as it is done!

I hope youve enjoyed this article! If you have any queries, ping me here or on Twitter, and I'll be happy to help you out.