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From "Seidl, Ed" <sei...@llnl.gov>
Subject mutations in a combiner?
Date Fri, 09 Mar 2012 18:58:58 GMT
I have a wacky question…is there any way to add data to a table from within a Combiner running
at compaction time?  Here's what I'm trying to achieve…

Let's say I have a table that stores some type of data that needs to be processed in some
way (binary, xml, it doesn't matter).  I may or may not receive all the data in one shot,
so as I populate the table, I do the processing (at least to the extent possible), and insert
a row with timestamp T1.  Some time later, I get another chunk of data for a given row and
insert it.  So now the row looks like

rowA CF:CQ:VIS:T1 = "start "
rowA CF:CQ:VIS:T2 ="end"

I can set up a combiner that will emit the value "start end", but now I want to re-process
that row.  The easiest way I can think of to do this is to have the combiner create an entry
in a second table with the row id I just merged, then a separate process can consume rows
from the indicator table and do the necessary processing.  Is this at all possible?  Or should
I just move all the combining logic to an external process?

Thanks,
Ed Seidl

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