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From "Liu, Raymond" <raymond....@intel.com>
Subject RE: How to implement this check put and then update something logic?
Date Fri, 10 May 2013 00:52:45 GMT
Any suggestion?

> Hi
> 	Say, I have four field for one record :id, status, targetid, and count.
> 	Status is on and off, target could reference other id, and count will record
> the number of "on" status for all targetid from same id.
> 	The record could be add / delete, or updated to change the status.
> 	I could put count in another table, or put it in the same table, it doesn't
> matter. As long as it can work.
> 	My question is how can I ensure its correctness of the "count" field when
> run with multiple client update the table concurrently?
> 	The closet thing I can think of is checkAndPut, but I will need two steps to
> find out the change of count, since checkAndPut etc can only test a single value
> and with EQUAL comparator, thus I can only check upon null firstly, then on or
> off. Thus when thing change during this two step, I need to retry from first step
> until it succeed. This could be bad when a lot of concurrent op is on going.
> 	And then, I need to update count by checkAndIncrement, though if the
> above problem could be solved, the order of -1 +1 might not be important for
> the final result, but in some intermediate time, it might not reflect the real
> count of that time.
> 	I know this kind of transaction is not the target of HBASE, APP should take
> care of it, then , what's the best practice on this? Any quick simple solution for
> my problem? Client RowLock could solve this issue, But it seems to me that it is
> not safe and is not recommended and deprecated?
> 	Btw. Is that possible or practice to implement something like PutAndGet
> which put in new row and return the old row back to client been implemented?
> That would help a lot for my case.
> Best Regards,
> Raymond Liu

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