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From Robert Coli <rc...@eventbrite.com>
Subject Re: Recommended amount of free disk space for compaction
Date Mon, 02 Dec 2013 19:57:01 GMT
On Thu, Nov 28, 2013 at 7:21 PM, Robert Wille <rwille@fold3.com> wrote:

> So here’s my question. If Cassandra only compacts one table at a time,
> then I should be safe if I keep as much free space as there is data in the
> largest table. If Cassandra can compact multiple tables simultaneously,
> then it seems that I need as much free space as all the tables put
> together, which means no more than 50% utilization.
>

If the number of SSTables is [x], then :

- "minor" compaction runs on 1-[x-1] SSTables (in practice, usually a
smaller number depending on config)
- "major" compaction runs on [x] SSTables

Unless you run a major compaction manually while using Size Tiered
Compaction, you are very unlikely to run a major compaction in normal
operation.

Level compaciton strategy has a different set of assumptions.

=Rob

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