How Savepoint store in persistent storage works ?

[pavneet_rana]

Hi to all,

I have read that SAP HANA is ACID compatible. And will not lose data if power goes off.

This is because changed pages and log are written in save point and written to persistent storage.

1. But where this stored in RAM or some kind of DISK ?.

As per understanding that once power off all RAM data will go off.

2. Then how save point/ log gets back the data into RAM ?.

Please can any one explain above 2 point ,if i am wrongly understood.

I shall be thankful to you for this.

Regards

Pavneet Rana

[Former Member · Accepted solution]

First, HANA stores all information in-memory.

Then, period save points are generated which contain a snapshot of the database, usually on SAS local storage or SAN network storage.

In between snapshots, a log is kept on fast disk. Usually on SSD local storage, or on SAN network storage.

In the event of a shutdown, the database creates a consistent state. On startup, database tables are typically loaded on demand, depending on configuration.

In the event of a power failure, the log is replayed, and this ensures the Integrity property of ACID in HANA.

[pavneet_rana · Accepted solution]

Thanks for reply.

So it mean that save point , which is snap shot of in-memory table is stored in some type of Hard disk.

And also the change log also same in hard disk.

So it mean that we are till storing the data in some type of hard disk, which will be used as back, in case of power failure. and thus will in-memory will get data back from hard-disk.

am i right ?.

please elaborate you point if i still understood wrong.

Regards

Pavneet Rana

[Former Member · Accepted solution]

Correct. Typically the log file is stored on a faster disk but both save point and log are persisted on disk.

In the future we expect this to change, as static RAM becomes available it will no longer be necessary to persist on disk, but this innovation is still years away.

There is more information available in the HANA Admin guide: http://help.sap.com/hana/SAP_HANA_Administration_Guide_en.pdf

[pavneet_rana · Accepted solution]

Thanks for reply,

I have few more doubt.

1. Does save point/snap shot mean are taking the complete back-up of in-memory table/view/sql procedure in database ?.

2. What type of databases we are using for this purpose ?.

3. Please can you give some example of such database ?.

Regards

Pavneet Rana

[Former Member · Accepted solution]

1. Yes, a copy of all tables, views, repository objects

2. And 3. I don't understand the questions

[pavneet_rana · Accepted solution]

Thanks for reply,

2 and 3 pint i mean to say.

That if we are taking backup for in-memory object, we need to store in some database.

which database we used for this purpose.

Example DB2 / oracle etc.

Regards

Pavneet Rana

[Former Member · Accepted solution]

I still don't understand your question. To repeat:

- HANA is an in-memory database

- A copy of the contents of this are stored on disk

If you want to backup, then you can backup to disk, or tape, like any other database. You don't need Oracle and DB2 as well as HANA.