Disk Space not freed up even after deleting keyspace from cassandra db and compaction

Question

I created a keyspace and a table(columnfamily) within it. Let's say "ks.cf"

After entering few hundred thousand rows in the columnfamily cf, I saw the disk usage using df -h.

Then, I dropped the keyspace using the command DROP KEYSPACE ks from cqlsh.

After dropping also, the disk usage remains the same. I also did nodetool compact, but no luck.

Can anyone help me out in configuring these things so that disk usage gets freed up after deleting the data/rows ?

Answer 1

Ran into this problem recently. After dropping a table a snapshot is made. This snapshot will allow you to roll this back if this was not intended. If you do however want that harddrive space back you need to run:

nodetool -h localhost -p 7199 clearsnapshot

on the appropriate nodes. Additionally you can turn snapshots off with auto_snapshot: false in your cassandra.yml.

edit: spelling/grammar

Answer 2

If you are just trying to delete rows, then you need to let the deletion step go through the usual delete cycle(delete_row->tombstone_creation->compaction_actually_deletes_the_row).

Now if you completely want to get rid of your keyspace, check your cassandra data folder(it should be specified in your yaml file). In my case it is "/mnt/cassandra/data/". In this folder there is a subfolder for each keyspace(i.e. ks ). You can just completely delete the folder related to your keyspace.

If you want to keep the folder around, it is good to know that cassandra creates a snapshot of your keyspace before dropping it. Basically a backup of all of your data. You can just go into 'ks' folder, and find the snapshots subdirectory. Go into the snapshots subdirectory and delete the snapshot related to your keyspace drop.