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From Benjamin Roth <>
Subject Re: Understanding of proliferation of sstables during a repair
Date Sun, 26 Feb 2017 21:01:35 GMT
Hi Seth,

Repairs can create a lot of tiny SSTables. I also encountered the creation
of so many sstables that the node died because of TMOF. At that time the
affected nodes were REALLY inconsistent.

One reason can be immense inconsistencies spread over many
partition(-ranges) with a lot of subrange repairs that trigger a lot of
independant streams. Each stream results in a single SSTable that can be
very small. No matter how small it is, it has to be compacted and can cause
a compaction impact that is a lot bigger than expected from a tiny little

Also consider that there is a theoretical race condition that can cause
repairs even though data is not inconsistent due to "flighing in mutations"
during merkle tree calculation.

2017-02-26 20:41 GMT+01:00 Seth Edwards <>:

> Hello,
> We just ran a repair on a keyspace using TWCS and a mixture of TTLs .This
> caused a large proliferation of sstables and compactions. There is likely a
> lot of entropy in this keyspace. I am trying to better understand why this
> is.
> I've also read that you may not want to run repairs on short TTL data and
> rely upon other anti-entropy mechanisms to achieve consistency instead. Is
> this generally true?
> Thanks!

Benjamin Roth

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