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From cem <cayiro...@gmail.com>
Subject Re: Cassandra 1.2 TTL histogram problem
Date Tue, 21 May 2013 21:43:31 GMT
Thank you very much for the swift answer.

I have one more question about the second part. Can method calculate
non-overlapping keys as overlapping? I mean it uses max and min tokens and
column count. They can be very close to each other if random keys are used.

In my use case I generate a GUID for each key and send a single write
request.

Cem

On Tue, May 21, 2013 at 11:13 PM, Yuki Morishita <mor.yuki@gmail.com> wrote:

> > Why does Cassandra single table compaction skips the keys that are in
> the other sstables?
>
> because we don't want to resurrect deleted columns. Say, sstable A has
> the column with timestamp 1, and sstable B has the same column which
> deleted at timestamp 2. Then if we purge that column only from sstable
> B, we would see the column with timestamp 1 again.
>
> > I also dont understand why we have this line in worthDroppingTombstones
> method
>
> What the method is trying to do is to "guess" how many columns that
> are not in the rows that don't overlap, without actually going through
> every rows in the sstable. We have statistics like column count
> histogram, min and max row token for every sstables, we use those in
> the method to estimate how many columns the two sstables overlap.
> You may have remainingColumnsRatio of 0 when the two sstables overlap
> almost entirely.
>
>
> On Tue, May 21, 2013 at 3:43 PM, cem <cayiroglu@gmail.com> wrote:
> > Hi all,
> >
> > I have a question about ticket
> > https://issues.apache.org/jira/browse/CASSANDRA-3442
> >
> > Why does Cassandra single table compaction skips the keys that are in the
> > other sstables? Please correct if I am wrong.
> >
> > I also dont understand why we have this line in worthDroppingTombstones
> > method:
> >
> > double remainingColumnsRatio = ((double) columns) /
> > (sstable.getEstimatedColumnCount().count() *
> > sstable.getEstimatedColumnCount().mean());
> >
> > remainingColumnsRatio  is always 0 in my case and the droppableRatio  is
> > 0.9. Cassandra skips all sstables which are already expired.
> >
> > This line was introduced by
> > https://issues.apache.org/jira/browse/CASSANDRA-4022.
> >
> > Best Regards,
> > Cem
>
>
>
> --
> Yuki Morishita
>  t:yukim (http://twitter.com/yukim)
>

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