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From Bruno Dumon <br...@outerthought.org>
Subject Re: Atomic update of a single row
Date Tue, 26 Jan 2010 20:53:34 GMT
The lock will in any case cause that writes don't happen concurrently.

But if a region server were to die between the updates to two column
families of one row (that are done in one Put operation), would the
update then be partially applied?

And that makes me also wonder: do these locks also apply to reads?
Thus, will all the updates to one row that are part of one Put
operation become visible 'atomicly' to readers?

Thanks for any clarification.


On Tue, Jan 26, 2010 at 8:02 PM, Jean-Daniel Cryans <jdcryans@apache.org> wrote:
> In get and put inside HRegion we call that line
> Integer lid = getLock(lockid, row);
> Even if you don't provide a row lock, it will create one for you and
> do the locking stuff. That happens before everything else, so is it
> fair to say that row reads are atomic?
> J-D
> On Tue, Jan 26, 2010 at 1:42 AM, Bruno Dumon <bruno@outerthought.org> wrote:
>> Hi,
>> At various places I have read that row writes are atomic.
>> However, from a curious look at the code of the put method in
>> HRegion.java, it seems like the updates of a put operation are written
>> to the WAL only for one column family at a time. Is this understanding
>> correct, so would it be more correct to say that the writes are
>> actually atomic per column family within a row?
>> On a related note, it would be nice if one could do both put and
>> delete operations on one row in an atomic manner.
>> Thanks,
>> Bruno

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