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From Ravi Agrawal <ragra...@clearpoolgroup.com>
Subject RE: Tombstone gc after gc grace seconds
Date Thu, 29 Jan 2015 21:28:40 GMT
Hi,
I saw there are 2 more interesting parameters –

a.       tombstone_threshold - A ratio of garbage-collectable tombstones to all contained
columns, which if exceeded by the SSTable triggers compaction (with no other SSTables) for
the purpose of purging the tombstones. Default value – 0.2

b.      unchecked_tombstone_compaction - True enables more aggressive than normal tombstone
compactions. A single SSTable tombstone compaction runs without checking the likelihood of
success. Cassandra 2.0.9 and later.
Could I use these to get what I want?
Problem I am encountering is even long after gc_grace_seconds I see no reduction in disk space
until I run compaction manually. I was thinking to make tombstone threshold close to 0 and
unchecked compaction set to true.
Also we are not running nodetool repair on weekly basis as of now.

From: Eric Stevens [mailto:mightye@gmail.com]
Sent: Monday, January 26, 2015 12:11 PM
To: user@cassandra.apache.org
Subject: Re: Tombstone gc after gc grace seconds

My understanding is consistent with Alain's, there's no way to force a tombstone-only compaction,
your only option is major compaction.  If you're using size tiered, that comes with its own
drawbacks.

I wonder if there's a technical limitation that prevents introducing a shadowed data cleanup
style operation (overwritten data, including deletes, plus tombstones past their gc grace
period); or maybe even couple it directly with cleanup since most of the work (rewriting old
SSTables) would be identical.  I can't think of something off the top of my head, but it would
be so useful that it seems like there's got to be something I'm missing.

On Mon, Jan 26, 2015 at 4:15 AM, Alain RODRIGUEZ <arodrime@gmail.com<mailto:arodrime@gmail.com>>
wrote:
I don't think that such a thing exists as SSTables are immutable. You compact it entirely
or you don't. Minor compaction will eventually evict tombstones. If it is too slow, AFAIK,
the "better" solution is a major compaction.

C*heers,

Alain

2015-01-23 0:00 GMT+01:00 Ravi Agrawal <ragrawal@clearpoolgroup.com<mailto:ragrawal@clearpoolgroup.com>>:
Hi,
I want to trigger just tombstone compaction after gc grace seconds is completed not nodetool
compact keyspace column family.
Anyway I can do that?

Thanks




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