Recommended way to use Tephra transaction in coprocessors

[Mohammad Adnan Raza]

Hello everyone,

I have requirement to use transaction in my hbase project. My requirement is - a client starts transaction and do some put operation. I'll have a coprocessor that will do few more puts. Now what I want is all these operation should go in single transaction. Meaning if client rollbacks her transaction my puts in coprocessor should also get rolledback.

My question is . is it possible to use transaction started in client in coprocessors? 

[Poorna Chandra]

Hi Mohammad,

If your co-processor executes before Tephra's co-processor then it can execute data operations using the client transaction.

If your co-processor updates the same row as the client Put, then just modify the client Put as required. Tephra co-processor will then execute the modified Put within the client transaction.

If you are adding new Puts then you'll need to copy the transaction attributes [1] from the client Put to your put. Tephra encodes the transaction as an attribute of the operation. Copying over the attributes will make the new Put also a part of the client transaction. 

On a rollback (rollback results in a Delete operation with "cask.tx.rollback" attribute),  you'll have to generate a corresponding Delete operation for your Puts.

You can do the same thing for Gets, Scans and Deletes too.

Apache Phoenix does something similar with Apache Phoenix and Tephra co-processors.

Thanks,

Poorna.

1 - Transaction attributes are cask.tx and cask.tx.rollback.

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[Poorna Chandra]

Hi Mohammad,

One more thing I missed mentioning for the case where you add new Puts - you'll have to use write pointer of the client transaction as the timestamp of the new Puts your co-processor creates. Tephra encodes client transaction as an attribute of operation called "cask.tx". TransactionCodec class can be used to decode the encoded transaction. 

Let me know if you have any questions.

Thanks,

Poorna.

[Mohammad Adnan Raza]

That's great help.

Thank you Poorna for prompt response. I'll try this and if I stuck somewhere I'll come come again :)

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       Mohd Adnan

       Feature Development Lead

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