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From "Takayuki Tsunakawa" <tsunakawa.ta...@jp.fujitsu.com>
Subject Re: How is column timestamp useful?
Date Mon, 10 May 2010 00:49:49 GMT
From: "tsuna" <tsunanet@gmail.com>
> > If saving memory (=keep memtable as small as possible) is
important,
> > you can set the maximum number of versions to 1.

> I don't think you'll be saving much memory anyway.  As Ryan already
> pointed out, when you overwrite a cell, a new version is created,
> regardless of the maximum number of versions you allow.  If you
> rewrite a cell 100 times in 5s, you'll end up with 101 versions, but
> only the last version will be visible to you.  You'll have to wait
> until a compaction "garbage collects" the 100 "unreachable", older
> versions.


I understood that, even if the maximum # of versions is 1, heavily
updated rows consume much memory up to the memtable size limit, and
minor compactions (memtable flush to disk) occur frequently. Then,
nessary versions (in this case, one version) is kept on disk.

Thank you.

Regards
- Takayuki





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