Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
HBase, mail # dev - Question on Coprocessors and Atomicity


Copy link to this message
-
Question on Coprocessors and Atomicity
Suraj Varma 2011-12-03, 14:24
I'm looking at the preCheckAndPut / postCheckAndPut api with
coprocessors and I'm wondering ... are these pre/post checks done
_after_ taking the row lock or is the row lock only done within the
checkAndPut api.

I'm interested in seeing if we can implement something like:
(in pseudo sql)
update table-name
set column-name = new-value
where (column-value - new-value) > threshold-value

Basically ... I want to enhance the checkAndPut to not just compare
"values" ... but apply an arbitrary function on the value _atomically_
in the Put call. Multiple threads would be firing these mutations and
I'd like the threshold-value above to never be breached under any
circumstance.

Is there a solution that can be implemented either via checkAndPut or
using coprocessors preCheckAndPut? If not, would this be a useful
feature to build in HBase?

Thanks,
--Suraj