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https://issues.apache.org/jira/browse/HBASE-16992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15631095#comment-15631095
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ChiaPing Tsai commented on HBASE-16992:
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Thanks for your explanation [~anoop.hbase] [~enis]
bq.It can be the same rows or different rows as Anoop says.
The main point i concern is the cells in one mutation may have different rows, 
because we merge the cells returned by CP into original mutation.
It makes mutation against the agreement of "Row" interface but is ok for 
HRegion#doMiniBatchMutate.

> The usage of mutation from CP is weird.
> ---------------------------------------
>
>                 Key: HBASE-16992
>                 URL: https://issues.apache.org/jira/browse/HBASE-16992
>             Project: HBase
>          Issue Type: Bug
>            Reporter: ChiaPing Tsai
>
> {code:title=HRegion#doMiniBatchMutate|borderStyle=solid}
> Mutation cpMutation = cpMutations[j];
> Map<byte[], List<Cell>> cpFamilyMap = cpMutation.getFamilyCellMap();
> checkAndPrepareMutation(cpMutation, replay, cpFamilyMap, now);
>  // Acquire row locks. If not, the whole batch will fail.
> acquiredRowLocks.add(getRowLockInternal(cpMutation.getRow(), true));
> if (cpMutation.getDurability() == Durability.SKIP_WAL) {
>   recordMutationWithoutWal(cpFamilyMap);
> }
> // Returned mutations from coprocessor correspond to the Mutation at index i. 
> We can
>  // directly add the cells from those mutations to the familyMaps of this 
> mutation.
> mergeFamilyMaps(familyMaps[i], cpFamilyMap); // will get added to the 
> memstore later
> {code}
> 1. Does the returned mutation from coprocessor have the same row as the 
> corresponded mutation? If so, the acquiredRowLocks() can be saved. If not, 
> the corresponded mutation may maintain the cells with different row due to 
> mergeFamilyMaps().
> 2. Is returned mutation's durability useful? If so, we should deal with the 
> different durabilities before mergeFamilyMaps(). If not, the 
> recordMutationWithoutWal can be saved. 
> 3. If both the returned mutation and corresponded mutation have 
> Durability.SKIP_WAL, the recordMutationWithoutWal() may record the duplicate 
> cells due to mergeFamilyMaps().
> Any comment? Thanks.



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