Can Hash File have more than one keys?

fyaqq · Post by **fyaqq** » Wed Sep 20, 2006 1:44 am

Some times I need to create hash files with more than one keys. But in the transformer stage, I can't look up what I want.
Thanks

ray.wurlod · Post by **ray.wurlod** » Wed Sep 20, 2006 2:21 am

A hashed file can have only one primary key (at a physical level), but it can have more than one column in that key. The total number of characters in all key columns may not exceed the number specified by MAXKEYLENGTH parameter in the uvconfig file.

To perform a lookup against a hashed file, a key expression must provide a value for each of the hashed file's key columns. It is NOT possible to perform a partial key lookup against a hashed file using a Hashed File stage, though it can be accomplished by a UV stage.

Edwink · Post by **Edwink** » Wed Sep 20, 2006 4:53 am

Ray, can u say wat wil be the lengthlimit for the primary key colum(physicallevel)?

ArndW · Post by **ArndW** » Wed Sep 20, 2006 7:39 am

EdWink - Ray did say what that length is - go to the uvconfig file in your DS directory and look for the value of MAXKEYLENGTH

kduke · Post by **kduke** » Wed Sep 20, 2006 7:42 am

The default is 768.

ray.wurlod · Post by **ray.wurlod** » Wed Sep 20, 2006 3:11 pm

In older versions (earlier than 6.0?) the default was 255. Nowadays it's 768, as Kim observes. Larger keys have implications for sizing the groups (pages) in the hashed file; after all, the entire key must be able to be stored. For example, the combination of 768-character keys and 512-byte pages simply would not work.
Recommended practice, for best performance, is to keep the size of hashed file keys (and, indeed, the size of hashed file data records) as small as possible.

rameshrr3 · Post by **rameshrr3** » Fri Sep 22, 2006 8:40 am

Edwink wrote:Ray, can u say wat wil be the lengthlimit for the primary key colum(physicallevel)?

alternatively on unix you can try this command from your OS command prompt

Code: Select all

$DSHOME/bin/smat -a | grep MAXKEYSIZE