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From lars hofhansl <lhofha...@yahoo.com>
Subject Re: MemStore and prefix encoding
Date Sat, 25 Aug 2012 21:57:21 GMT
The prefix encoding applies to blocks in the HFiles and in the block cache, but not to the

#1 Yes. Each column family is its own store. All stores are flushed together, so have many
add overhead (especially if a few tend to hold a lot of data, but the others don't, leading
to very many small store files that need to be compacted).
#2 There is only one key with the same key, column family, qualifier, and timestamp (if you
write multiple with the same timestamp it is undefined which one you'll get back when you
read the next time). So that does not make sense. Writes with the same key, column family,
qualifier (each with a different timestamp) count towards the version limit.

-- Lars

----- Original Message -----
From: Eric Czech <eric@nextbigsound.com>
To: user <user@hbase.apache.org>
Sent: Saturday, August 25, 2012 2:44 PM
Subject: MemStore and prefix encoding

Hi everyone,

Does prefix encoding apply to rows in MemStores or does it only apply
to rows on disk in HFiles?  I'm trying to decide if I should still
favor larger values in order to not repeat keys, column families, and
qualifiers more than necessary and while prefix encoding seems to
negate that concern for storage on disk, I'm not sure if it's still
applicable to in-memory storage.

Also, I had two other quick (unrelated) questions and I assume it'd be
less annoying if I put them all in one email:

1.  Do column families defined for a table introduce any overhead for
rows that don't put any values in them?  I don't think that's the case
but I wanted to be sure.

2.  Do writes with the same key, column family, qualifier, and
timestamp count towards the version limit?

Thanks for the help!

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