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From Jeff Jirsa <>
Subject Re: Massive deletes -> major compaction?
Date Thu, 21 Sep 2017 18:51:01 GMT
The major compaction is most efficient but can temporarily double (nearly) disk usage - if
you can afford that, go for it.

Alternatively you can do a user-defined compaction on each sstable in reverse generational
order (oldest first) and as long as the data is minimally overlapping it’ll purge tombstones
that way as well - takes longer but much less disk involved. 

Jeff Jirsa

> On Sep 21, 2017, at 11:27 AM, Durity, Sean R <> wrote:
> Cassandra version 2.0.17 (yes, it’s old – waiting for new hardware/new OS to upgrade)
> In a long-running system with billions of rows, TTL was not set. So a one-time purge
is being planned to reduce disk usage. Records older than a certain date will be deleted.
The table uses size-tiered compaction. Deletes are probably 25-40% of the complete data set.
To actually recover the disk space, would you recommend a major compaction after the gc_grace_seconds
time? I expect compaction would then need to be scheduled regularly (ick)…
> We also plan to re-insert the remaining data with a calculated TTL, which could also
benefit from compaction.
> Sean Durity
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