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From Stack <st...@duboce.net>
Subject Re: Filter with State
Date Wed, 01 Aug 2012 22:44:16 GMT
On Wed, Aug 1, 2012 at 10:44 PM, Jerry Lam <chilinglam@gmail.com> wrote:
> Hi HBase guru:
>
> From Lars George talk, he mentions that filter has no state. What if I need
> to scan rows in which the decision to filter one row or not is based on the
> previous row's column values? Any idea how one can implement this type of
> logic?

You could try carrying state in the client (but if client dies state dies).

You can't have scanners carry state across rows.  It says so in API
http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/filter/package-summary.html#package_description
(Whatever about the API, if LarsG says it, it must be so!).

Here is the issue: If row X is in region A on server 1 there is
nothing to prevent row X+1 from being on region B on server 2.  How do
you carry the state between such rows reliably?

Can you redo your schema such that the state you need to carry remains
within a row?
St.Ack

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