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From Jan Kesten <j.kes...@enercast.de>
Subject Re: Nodetool clearsnapshot
Date Tue, 13 Jan 2015 14:18:25 GMT
Hi,

> I have read that snapshots are basicaly symlinks and they do not take 
> that much space.
> Why if I run nodetool clearsnapshot it frees a lot of space? I am 
> seeing GBs freed...

both together makes sense. Creating a snaphot just creates links for all 
files unter the snapshot directory. This is very fast and takes no 
space. But those links are hard links, not symbolic ones.

After a while your running cluster will compact some of its sstables and 
writing it to a new one as deleting the old ones. Now for example you 
had SSTable1..4 and a snapshot with the links to those four after 
compaction you will have one active SSTable5 which is newly written and 
consumes space. The snapshot-linked ones are still there, still 
consuming their space. Only when this snapshot is cleared you get your 
disk space back.

HTH,
Jan



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