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Date: Tue, 17 Jan 2012 13:27:12 -0800 (PST)
From: lars hofhansl <lhofhansl@yahoo.com>
Reply-To: lars hofhansl <lhofhansl@yahoo.com>
Subject: Limited cross row transactions
To: hbase-dev <dev@hbase.apache.org>
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I just committed HBASE-5203 (together with HBASE-3584 this implements atomic row operations).
Although a relatively small patch it lays the groundwork for heterogeneous operations in a single WALEdit.

The interesting part is that even though the code enforced the atomic operation to be a for single row, this is not required.
It is enough if all involved KVs reside in the same region.

I am not saying that we should add any high level concept to HBase (such as the EntityGroups of Megastore).

But, with a slight addition to the API (allowing a grouping of multiple row operations) client applications have all the building blocks to do limited cross row atomic operations.
The client application would be responsible for either correctly pre-splitting the table, or a custom balancer has to be provided.

The operation would fail if the regionserver determines that it would need data from multiple region servers.

I think this needs at least minimal support from HBase and cannot (efficiently or without adding more moving parts) by a client API only.


Comments? Is this worth pursuing? If so, I'll file a jira and provide a patch.

Thanks.


-- Lars