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From "Raymond Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8542) Need a more common and capable atomic row mutation
Date Tue, 14 May 2013 03:19:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8542?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13656674#comment-13656674

Raymond Liu commented on HBASE-8542:

bq.For more than one comparison, how do we express their relationship (and, or, etc) ?

originally, I thought it will be "and" for all the condition. if complicate expression needed,
I don't know is there a good way to implement them? seems to me not a easy task.

bq. Is beforeafterflag an enum or a boolean ?If the flag is boolean, would two maps (one for
before, one for after) be better ?
hmm, good idea, two mpas might be better.

bq. The list of mutations should be applied all or none, right ?

Yes, since we are on a single row, originally, I am image a PUT/Delete/increment here. that
already been satisfied by current implementation. I am not sure if put/delete/increment been
mixed here, is that atomic still been easy to be implemented?
> Need a more common and capable atomic row mutation
> --------------------------------------------------
>                 Key: HBASE-8542
>                 URL: https://issues.apache.org/jira/browse/HBASE-8542
>             Project: HBase
>          Issue Type: Improvement
>          Components: Client, regionserver
>    Affects Versions: 0.95.0
>            Reporter: Raymond Liu
> Hi
> For Atomic row mutation, currently , there are CheckAndPut/Delete and people ask for
more CheckAndMutation like API,  also Increment/IncrementColumnValue are available. However
there are a lot of limitation of these approaching. Say :
> 1. The CheckAndMutation family can only check upon one value upon equal condition and
upon single column. This is quite limited, you probably want to compare two column, or need
more CompareOp (  for CompareOp, the lower level code can support different CompareOp, we
probably could export them to client API level.)
> 2. The mutation can only be done upon success, do not have a fail branch to perform another
operation. In order to implement branching at client level , you need to loop and check upon
a serial different conditions and fall back from the beginning upon anyone fails. Sometime
even this loop approaching can not full fill the requirements.
> 3. The CheckAndMutation don't return value, it's ok now, since it only do mutation upon
equal, while if you support more CompareOp, you have no way to know what's the original value
been changed.
> 4. Value can only be a constant one , could not reference other column
> 5. For ICV, well, it is only self referenced, could not check upon other column and increase.
Thus limit the usage.
> In HBASE-2322, it said "We provide a compare-and-swap primitive, which is sufficient
to achieve the same effect as row locks from the client side" But I don't see this is easy
and seems to me only ICV is compare and swap primitve the others just do compare and set.
> To give a few example which I think are quite common simple cases, while could not be
easily satisfied now :
> Case 1:  SQL like INSERT ON DUPLICATE, you want to insert a new row if there are no duplicate
row exist, while you want to update some column if there are already existing row.
> Case 2: Upon update/add/delete a row which have one size column employ the value say
'S'/'M'/'L',  a count number also need to be updated according to the size column. In order
to achieve this, you need to get the old size value to correctly figure out the count changes.
Thus you need an atomic operation for Get+Put on the size column ( though you could do this
job by looping through different value for check, just to figure out what the original value
it is. But we could surely do better than this. Say if you got hundreds of status instead
of three?)
> If you like , I am sure you can also think out more similar cases that you require a
more capable row mutation.
> Thus I am wondering, can we provide a common atomic row mutation API like :
> AtomicRowMutation( Map<KV, CompareOp> compare,  List<KV|Column>onSuccessMutation,
 List<KV|Column>onFaileMutation,  Map<Column, beforeafterflag> ColumntoReturn)
> Well , I believe you expert surely could figure out API better than this.
> The point is that I guess this won't be very hard to been implemented since in the current
CheckAndMutation/Increment code path, most thing is available and not much additional logic
is needed. API like this one might not solve all the issue  that people might ask for atomic
row mutation ( and which could be solved by the deprecated buggy rowLock). But I guess it
can solve majority of the mutation that involve a single row instead of cross row.  At least
for my own use cases.
> Any ideas?

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