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Monitor the rollback progress

Former Member
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Hi Team,

Wanted to know, if suppose i cancel a job. Wanted to know if we can monitor the rollback progress. Undo data is stored in the data volumes but wanted to track it if its possible.

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Answers (1)

Former Member
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Has anyone tried to monitor the rollback area in hana?

Former Member
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Hi Folks,

Has anyone tried to attempt track the rollback progress.

Suppose i have a job running in SAP, i cancel it sql trace is the only option i see for tracking rollback progress. That too i cannot properly see it.

How much data has been rolled back or else what sql query was being run.

Mechanism of rollback is still kind of abstract to me.

Former Member
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Usually I only answer if I can add value, but as you explicitly asked me to comment this topic, I make an exception: I am not aware about a possibility to monitor rollbacks. In fact I haven't come across this possibility with other database like Oracle, either.

Former Member
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Martin,

Thanks so much for the response and thank you for making an exception.

The question is like this, how are we managing undo and then rollback of that data.

How does it work in HANA. we would love to know more about the control flow as to how it works in SAP HANA.

Now in db2 we can use "db2 get snapshot for all applications global" and then track the rollback progress.

Former Member
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Roughly speaking the following happens during a rollback in SAP HANA environments:

"In case a transaction is rolled back, write locks are released and transaction-specific change information of the consistent view manager is deleted. The versions remain in delta storage until the next merge operation but they will not be visible for any transaction."

So compared to other databases the rollback work is minor with SAP HANA due to the delta storage concept. Uncommitted data is never merged into the main and so we are sure that a rollback never has to touch the typically large main storage.

Former Member
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What happen if a savepoint is also triggered during the same time.

Former Member
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Nothing special, the savepoint is written as usual. I would guess that it treats the rollback like any other uncommitted transaction.

Former Member
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So then the delta pages would also be written into the disk since a savepoint has been triggered and during the phase of the rollback those pages would be changed right?

Former Member
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Yes, of course also the delta storage is persisted (-> delta log).

Former Member
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Martin,

Thanks so much for the insight. Dont you think this is an area which is kind of greyish and not much documentation has been mentioned. Here in DB2 whenever we see rollbacks we get the alerts related to log full situations. Wanted to understand in depth of the control flow as to how it happens in HANA.

Former Member
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I am not a DB2 expert and there might be some design details that result in an increased criticality of rollbacks. For other databases like Oracle and SAP HANA I neither see a significant risk of rollbacks nor an increased need for alerting.

Former Member
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just to recap as to what i have understood. We have the main and delta , during an update and delta gets updated and if a savepoint gets triggered then its written to the disk.

Now if we want to rollback then it gets rolled back from delta portion of the data and the next savepoint will change it on the disk as well right martin.