SAP HANA(Redo ,undo and savepoints)

[Former Member]

Hello experts,

Kindly give the details about undo and redo log pages in HANA and what they conatin exactly.

Also what is save point.

Thanks and Regards,

AJ

[former_member192811]

Hello Akshay,

Whenever any application requests for any transaction  on data in memory it is first written to a log volume which is nothing but a hardisk and external to RAM. This is referred to as redo log. Redo log holds following information:

Start of transaction

Commit of Transaction or abort of transaction

update details:

Value before update(undo log) and Value after update(redo log).

Once written to log volume the data is then written to RAM and then to disk or data volume every 5 mins which the default value and can be configured.

In data volume a savepoint is built of committed transactions .It represents consistent state of db. From a savepoint a system can be successfully restored.In the event power goes the redo log or log volume is read to restore  from the last savepoint on data volume and onwards.

In case for transactions which were not written to redo log and were uncommitted are written to undo log and they are stored in data volume not in log volume. Redo logs are in log volume.

For recovery both redo, undo and savepoints are read for restoration.

Hope that helps.

Regards,

Pooja M

[Former Member]

Thanks pooja.

Regards,

Akshay

[former_member767989]

I have question here please it's very urgent I understand that sap hana has got two section s of RAM volatile and non volatile do when we commit a transaction it crates a log entry in log volume and there is page management technique through which thd changed data or Insert,updates,delete ate written at regular interval yo persistent memory or non volatile RAM now in case of power failure or system crash when we restart database we can get the commuted data back since it's saved but during the page movement from volatile yo non volatie memmory if in a page which contains 4 transactions halfnof them are written to persistent storage and due tpowet loss remmsing 2 could not be written then in this case which transaction is committed snd which is not please there a big confusion I am having on this please if tiis can be addressd