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
