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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Trivial Update of "Hbase/JSONRest" by Michael Gottesman
Date Mon, 11 Aug 2008 01:10:03 GMT
Dear Wiki user,

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The following page has been changed by Michael Gottesman:
http://wiki.apache.org/hadoop/Hbase/JSONRest

------------------------------------------------------------------------------
  Please read this before you go further to the usage section. I envision two sorts of users
of JSONRest at the moment: the normal database user, and the timestamp database user.
  
  === For Normal Database Users ===
- I imagine that many people just want to use HBase as a normal database that can scale to
large loads. This does not necessarily require the usage of the timestamp side of HBase. In
this user's mind when he/she overwrites data, it is destroyed. REMEMBER IT IS NOT DESTROYED.
When you overwrite data in HBase through the usage of the non-timestamp part of the Client
API, all that you are doing is writing another Cell at a sooner timestamp. This will cover
up the older versions of the Cell. They are still there, just hidden if you use the non-timestamp
methods. They will still be there and be accessible via the timestamp methods until enough
old timestamp Cells accumulate that HBase cleans them up. This is done via a configuration
setting which allows you to set the number of different timestamp versions of a cell can exist
before HBase deletes the latest value.
+ I imagine that many people just want to use HBase as a normal database that can scale to
large loads. This does not necessarily require the usage of the timestamp side of HBase. In
this user's mind when he/she overwrites data, it is destroyed. REMEMBER IT IS NOT DESTROYED.
When you overwrite data in HBase through the usage of the non-timestamp part of the Client
API, all that you are doing is writing another Cell at an earlier timestamp. This will cover
up the older versions of the Cell. They are still there, just hidden from view if you do not
explicitly get them via the Client API Timestamp Methods. And, they will still be there and
be accessible via the timestamp methods until enough old timestamp Cells accumulate that HBase
cleans them up. This is done via a configuration setting which allows you to set the number
of different timestamp versions of a cell can exist before HBase deletes the latest value.
  
  === For Timestamp Database Users ===
  All the methods without timestamps use HConstants.LatestTimestamp (sp?), so you can still
use them if you want to create a new entry with the latest timestamp or delete the latest
entry.

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