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From Edward Capriolo <>
Subject Re: memtable sstable questions (0.6.4)
Date Wed, 20 Oct 2010 19:01:05 GMT
On Wed, Oct 20, 2010 at 2:47 PM, CassUser CassUser <> wrote:
> Hey,
> As I understand it writes go directly to the commit log.  Once a threshold
> has been reached the data is shipped to a memtable, and again to an sstable.
> 1. How many memtables are created when a flush happens from a commit log?
> One per CF?
> 2. Is there any space associated with an empty memtable?
> 3. When a flush happens from a memtable to an sstable, does this create a
> single new sstable?
> 4. Should compaction be turned off during a large data load?
> Thanks.

Take a look at:

1 and 3
Memtables flush for three reasons size, time, and number of
operations. There is one memtable per column family. Each memtable
flushes individually.

2. Is this a trick question?

4. Should compaction be turned off during a large data load?
You can disable compaction during bulk loads. This can help because
otherwise the same data might be compacted multiple times. However if
you go to long with compaction turned off you end up with multiple
sstables. This can end up in fragmented rows.

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