ospike-examples.aero-multi-record-txn.0.01.source-code.design.txt Maven / Gradle / Ivy

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1)

For each update, record the previous state of the record prior to the update and hold this in a record with PK=TXN_ID.
Put the start time of the txn in here as well.
Use a map to hold the ‘old’ versions ( so looks like {PK_1:Record1_v1, PK_2:Record2_v2, … }

DONE

2)

If you are updating a record with PK  then to lock the record insert a record with PK _LOCK.
This will fail if someone else has locked the record. Include TXN_ID in the record. Rollback ( see below ) if locking fails

DONE

3)

On completion of the txn delete your PK=TXN_ID record ( this is your commit step) , followed by your locks.

DONE

4)

Rollback happens asynchronously ( or could be invoked) . TXN records more than a certain age get rolled back.

DONE

5)

If you fail while updating PK_1, PK_2 in steps 1 & 2 etc rollback will be able to restore the previous versions of the records.
The TXN record is deleted once the data restore is complete - this marks rollback complete
After rollback complete, delete the record locks.

DONE

6)

If you fail while removing locks in step 3, a separate time out process will traverse the locks periodically and remove orphan records
i.e. those which do not have an existing txn id and are beyond a certain age
This situation can occur when

1)  A txn record has been deleted ( means txn complete ) but deletion of locks did not run to completion.
2)  Lock taking initiated but associated txn record not written

DONE