Bug: Add --older-than option to nodetool clearsnapshot
Status: Resolved
Priority: Normal
Resolution: Fixed
Created: 17/Aug/21 05:17
Resolved: 27/Sep/22 22:02

h1. Summary

Opening this issue in reference to [this WIP PR|https://github.com/apache/cassandra/pull/1148]:

This functionality allows users of Cassandra to remove snapshots ad-hoc, based on a TTL. This is to address the problem of snapshots accumulating. For example, an organization I work for aims to keep snapshots for 30 days, however we don't have any way to easily clean them after those 30 days are up.

This is similar to the goals set in: https://issues.apache.org/jira/browse/CASSANDRA-16451 however would be available for Cassandra 3.x.
h1. Functionality

This adds a new command to NodeTool, called {{expiresnapshot}} with the following options:

NAME
 nodetool expiresnapshots - Removes snapshots that are older than a TTL
 in days

SYNOPSIS
 nodetool [(-h <host> | --host <host>)] [(-p <port> | --port <port>)]
 [(-pw <password> | --password <password>)]
 [(-pwf <passwordFilePath> | --password-file <passwordFilePath>)]
 [(-u <username> | --username <username>)] expiresnapshots [--dry-run]
 (-t <ttl> | --ttl <ttl>)

OPTIONS
 --dry-run
 Run without actually clearing snapshots

-h <host>, --host <host>
 Node hostname or ip address

-p <port>, --port <port>
 Remote jmx agent port number

-pw <password>, --password <password>
 Remote jmx agent password

-pwf <passwordFilePath>, --password-file <passwordFilePath>
 Path to the JMX password file

-t <ttl>, --ttl <ttl>
 TTL (in days) to expire snapshots

-u <username>, --username <username>
 Remote jmx agent username

The snapshot date is taken by converting the default snapshot name timestamps (epoch time in miliseconds). For this reason, snapshot names that don't contain a timestamp in this format will not be cleared.
h1. Example Use

This Cassandra environment has a number of snapshots, a few are recent, and a few outdated:

root@cassandra001:/cassandra# nodetool listsnapshots
 Snapshot Details:
 Snapshot name Keyspace name Column family name True size Size on disk
 1529173922063 users_keyspace users 362.03 KiB 362.89 KiB
 1629173909461 users_keyspace users 362.03 KiB 362.89 KiB
 1629173922063 users_keyspace users 362.03 KiB 362.89 KiB
 1599173922063 users_keyspace users 362.03 KiB 362.89 KiB
 1629173916816 users_keyspace users 362.03 KiB 362.89 KiB

Total TrueDiskSpaceUsed: 1.77 MiB

To validate the removal runs as expected, we can use the `--dry-run` option:

root@cassandra001:/cassandra# nodetool expiresnapshots --ttl 30 --dry-run
 Starting simulated cleanup of snapshots older than 30 days
 Clearing (dry run): 1529173922063
 Clearing (dry run): 1599173922063
 Cleared (dry run): 2 snapshots

Now that we are confident the correct snapshots will be removed, we can omit the {{--dry-run}} flag:

root@cassandra001:/cassandra# nodetool expiresnapshots --ttl 30
 Starting cleanup of snapshots older than 30 days
 Clearing: 1529173922063
 Clearing: 1599173922063
 Cleared: 2 snapshots

To confirm our changes are successful, we list the snapshots that still remain:

root@cassandra001:/cassandra# nodetool listsnapshots
 Snapshot Details:
 Snapshot name Keyspace name Column family name True size Size on disk
 1629173909461 users_keyspace users 362.03 KiB 362.89 KiB
 1629173922063 users_keyspace users 362.03 KiB 362.89 KiB
 1629173916816 users_keyspace users 362.03 KiB 362.89 KiB

Total TrueDiskSpaceUsed: 1.06 MiB
h1. Next Steps

To be completed:
 - Tests
 - Documentation updates

I am a new to this repository, and am fuzzy on a few details even after reading the contribution guide 😅 Any advice on the following would be greatly appreciated!
 - What branch would this type of change be merged into? Currently, I'm targeting {{apache:trunk}} by default
 - Is there a test strategy/pattern for this type of change? I was not able to find any existing tests for similar {{nodetool}} commands

Thanks! 😄