DSXchange

Hi,

When do we use static hashed file and on which basis do we define it?

thanks in advance.

Whenever you like, provided you don't mind incurring the additional monitoring and maintenance overheads. It's defined on the basis of "file type" (the "create file" options in the Hashed File stage); type 30 is a dynamic hashed file; types 2-18 are static hashed files. The best candidates for static hashed files are those in which the number of records and/or total data volume is essentially unchanging (static), for example a table of country codes.

ray.wurlod wrote:Whenever you like, provided you don't mind incurring the additional monitoring and maintenance overheads.

Ray, could you expand a little bit on this please? Not looking for a Full Wurlod or anything, but curious what you meant by 'additional monitoring and maintenance overheads'.

Thanks.

When a static hashed file is created you have to specify the size and number of groups (pages). If the volume of data is likely to change these values may become outdated. You need to monitor the level of overflowed groups and resize when necessary. This is managed automatically in dynamic hashed files, which is why they are to be preferred when the volume of data is likely to change.

You also need to choose one from among 17 hashing algorithms; a wrong choice will lead to "clumping" (over-full and near-empty groups). Dynamic hashed files have only two, and the choice is very easily made.

Gotcha... thanks again.