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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: limit on number of blocks per HFile and files per region
Date Fri, 24 Aug 2012 00:18:23 GMT
Inline. In general I'd recommend you read the documentation more
closely and/or get the book.

J-D

On Thu, Aug 23, 2012 at 4:21 PM, Pamecha, Abhishek <apamecha@x.com> wrote:
> 1.       Can there be multiple row keys per block and then per  HFile? Or is a block
or Hfile dedicated to a single row key?

Multiple row keys per HFile block. Read
http://hbase.apache.org/book.html#hfilev2

> I have a scenario, where for the same column family, some rowkeys will have very wide
rows, say rowkey W, and some rowkeys will have very narrow rows, say rowkey N. In my case,
 puts for rowkeys W and N are interleaved with a ratio of say 90 rowkeyW puts vs 10 rowkeyN
puts. On the get side, my app works on getting data for a single  rowkey at a time.
> Will that mean for a rowkeyN, the entries will be scattered across regions on that same
region server, given there are interleaved puts? Or Is there a way I can enforce contiguous
 writes to a region/Hfile reserved for rowkey N.  This way, I can leverage the block cache
and have the entire/most of  rowkeyN fit in there for that session.

The row keys are sorted according to their lexicographical order. See
http://hbase.apache.org/book.html#row

If you don't want the big rows coexisting with the small rows, put
them in different column families or different tables.

> 2.       Is there a limit on number of HFiles that can exist per region?

I think your understanding of HFiles being a bit wrong prompted you to
ask this, my previous answers probably make it so that you don't need
this answer anymore, but there it is just in case:

The HFiles are compacted when reaching
hbase.hstore.compactionThreshold (default of 3) per family, and you
can have no more than hbase.hstore.blockingStoreFiles (default of 7).

" Basically, on what criteria does a rowkey data gets split in two
regions [on the same region server]. I am assuming there can be many
regions per region server. And multiple regions for the same table can
belong in the same region server.

A row key only lives in a single region since the regions are split
based on row keys.

> 3.       Also, is there a limit on the number of blocks that are created per HFile?

No.

> What determines whether a split is required?

hbase.hregion.max.filesize, also see
http://hbase.apache.org/book.html#disable.splitting if you want to
change that.

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