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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: LevelDB type compaction
Date Thu, 15 Sep 2011 22:30:58 GMT
On Thu, Sep 15, 2011 at 3:05 PM, mcasandra <mohitanchlia@gmail.com> wrote:
> With Leveldb is it going to make reads slower

No.

Qualified: compared to "major compaction" under the tiered strategy,
leveled reads will usually be a little slower for update-heavy loads.
(For insert-mostly workloads compaction doesn't really matter.)  But
major compaction is not practical in production; you want something
that gives consistently good performance, rather than good performance
once a day or once a week and then degrades quickly.

> my understanding is it
> will create more smaller files

Yes.

> and updates could be scattered all over
> before compaction?

No, updates to a given row will be still be in a single sstable.

> Also, when memtables are flushed, does it create small
> files too since memtable size would generally be bigger than 2-4MB?

Level0 (newly flushed) sstables are not size-limited.  This is one of
a handful of differences we have over leveldb itself, which remains a
good overview (http://leveldb.googlecode.com/svn/trunk/doc/impl.html).

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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