Hashmap

Database
KVB
N/A

Hashmap

Hi 

Is there any chance like if the data is huge then the hash map gets filled completely and hashing stops?

Regards

KVB

4 REPLIES

Re: Hashmap

Hashing won't stop but there may be a scenario of hash collisions. Where two different primary index rows would get same hash value.

To resolve this there exist one more 32 bit values generated called uniqueness values (added to hash value)

-Sri

Re: Hashmap

I agree with Sri, if the there is huge number of rows with small hash map, hashing would not stop, rather hash collsion will occure. A 32 bit uniqueness values is used to differentiate between the hash collisions. in TD 14, a larger hash map is introduced to avoid hash collisions. 

Khurram

Re: Hashmap

Hi Saeed,

On what basis number of Hashmap buckets will be decided? Let's say I have a Teradata system with 100 AMPS installing on 64bit SUSE linux, then howmany buckets will be created in Hashmap to hold AMP numbers?

Thanks in advance.

Sri.

N/A

Re: Hashmap

The number of hash buckets is always the same, 2**20 = 1,048,576

There's a process to fill the hash buckets for a n-AMP systems with numbers between 0 and n-1 during sysinit.

See the Database Design manual:

http://www.info.teradata.com/HTMLPubs/DB_TTU_15_00/Database_Management/B035_1094_015K/ch08.060.068.h...