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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Online modify table schema (e.g. AddColumnFamily, DeleteColumnFamily, etc) and other features
Date Thu, 20 Jan 2011 18:48:58 GMT
To complement what jgray answered...

> 2. Different memstore/memtable-size and region-size for different table.
>    This feature is useful for different tables for different applications.
>     Is there a plan to support it?

Have you taken a look at the table properties? In the shell you can
tune MAX_FILESIZE and MEMSTORE_FLUSHSIZE to do exactly what you

> 3. Periodic flush.
>    Current HBase only flush memstore to HFile by memory size thresholds.
>    If a Region-Store is quiet for a long time (such as 2 hours) for a
> write-dense application, the periodic flush can free more memory.
>    Is there a plan to support it?

If a region isn't written to, and there's a write-heavy job going on,
then as the HLogs get created it's easy to reach the max number of
HLogs a RS can get (32 by default) and after that point the memstores
for the oldest edits will be flushed. If it's really inserting a lot
of data, I expect that it can takes less than an hour to force flush
unused memstores. Check out HLog.cleanOldLogs and

It's not really periodic or easily configurable tho.


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