distribution and access details for fallback amps

Database
Enthusiast

distribution and access details for fallback amps

Hi,

We know that rows distribution takes place based on Row hash value of primary index column of the table. Can anyone tell how the distribution of data amongst the fallback amps take place? Also, when the amp is down, how the data is read from the Fallback amp? Basically, please tell as what  governs the distribution and access of Fallback data.

3 REPLIES
Supporter

Re: distribution and access details for fallback amps

Check the manuals on the HashMaps - there exits two. One primary, one for the fallback. The two hashmaps gurantees that the fallback data will be placed on a different cluster. 

In case DB detects that an VPROC is down and table is fallback it will use the fallback hashmap to locate the fallback data.

Enthusiast

Re: distribution and access details for fallback amps

Ulrich, the fallback row is always in the same cluster as the primary. 

Supporter

Re: distribution and access details for fallback amps

Jim, yes you are right - I used the wrong term, was thinking of the cabinet - but this depends on your HW... 

Section AMP Clustering and Fallback in the Database Administration doc is explaining it good.

The other important considerations are

For AMP failures due to hardware-related problems, to protect the availability of your data,

define AMP clustering assignments as closely as possible to the following fault-tolerant

strategy. No two or more AMPs in a cluster:

• On the same node (for MPP systems).

• In the same node cabinet.

• Serviced by the same disk array cabinet.

• Serviced by the same disk array controller.