Hello and welcome to the SAP HANA Academy.
The topic of this video tutorial series is SAP HANA 2.0 SPS 03, What’s New?
and in this video we will take a look at a new system administration command line tool: hdbmdcutil
Hi, I am Denys van Kempen.
Most of the SAP HANA administrators listening in will be familiar with the hdbnsutil command line tool
HANA database nameserver utility.
It is a bit like the Swiss army knife for different system management tasks and activities
like changing the encryption root keys, changing the network the services listen to,
configuring and managing system replication, and so on.
As of SPS 03, we now have another tool for system management:
hdbmdcutil, the HANA database multi-tenant database container utility.
There is only one flag so far: -restoreTopology
and this initializes the topology with the content from a topology backup file.
When would you want to use it? When the storage, the persistence, of the
system database has been damaged and cannot be recovered. You also do not have a backup.
If you do have a backup, use that - you would be much better off.
Initializing means exactly that back to the initial, the original, state, so no license,
for example, or whatever changes you have made to the system database.
It is more of a last resort option
you will have some trouble getting the XS
Advanced environment back up after a system database re-init, for example.
Might need to be reinstalled. However, the system database does not contain
any user data,which typically tends to be the most important So, a reinit of the systemdb
might be an important lifeline to get out of the water and start again.
Like I said before, in the extremely unlikely event that there is no backup of the system database.
Let’s do a little simulation.
Do NOT repeat after me on your production system.
This is just to show how a disaster might look like.
HDB info - This is our HANA system up and running
Now, lets list the contents of the file system for our system T02.
We have three directories. The first is for the nameserver, the system database that is.
Number two and three are the indexserver for
the first tenant and its xsengine process. You can look that up with a bit of SQL.
OK - let’s simulate we loose the storage for our system database. I will just remove the file.
OK - HDB info - HANA is still up but it would probably crash soon.
Let’s stop the system - HDB stop
Now, we can run our command hdbmdcutil -restoreTopology
Loading initial topology from a JSON file.
Creating persistence - this takes a bit of time.
Minute or so, on my system and if you want to know what the password
is for the system user, it is probably a good idea to specify that as well here as well.
OK - Done. Let’s check if our nameserver database file
is back on persistence. Yes, it is - with the current time stamp
We can start HANA up again - HDB start and we are back in business.
For those interested, here is the JSON file, by the way, that hdbmdcutil used to reinitialize
the system database. That’s all that is needed.
The hdbmdcutil command line tool and the initialization procedure for the system database is documented
in Note 2588284. No reference yet, in the regular SAP HANA
documentation on the SAP Help Portal, so should you need to use the tool, it is
probably best to first contact SAP support. Well, That’s it.
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