Via va Viaindex

[Richard Witkopp]

Really? That may have been true 5 years ago, but I thought
most modern versions of databases would let you specify the
index.

> Mark,  
> 
> Most database optimizers will not quarantee that if you give 
> them an Index
> to use, they will use it. They may decide that the index is 
> not the optimal
> method of retrieval. (depending on the amount of data and the 
> kind of data
> in the table). I believe that some database don't even allow 
> you to specify
> an index on retrieval.  Because of that PowerHouse doesn't 
> pass the VIAINDEX
> information to the database at all.  We pass the list of 
> segments and the
> ordering information instead. This allows the database to 
> decide for itself
> which path is the optimal one for it to use in each case.  
> The ordering
> request quarantees that the information is retrieved in a 
> consistent order
> regardless of how the database retrieved it.  In this way we 
> are using the
> database as efficiently as we can, letting it use its, hopefully
> intelligent, information base to determine how best to get 
> you the data you
> requested.
> 
> Syntacticly, use of VIAINDEX, for relational databases is a kind of
> shorthand for VIA a,b,c ORDERED, which is the information 
> that will be sent
> to the database.  With VIAINDEX, you can override the 
> defaults by specifying
> the VIA segments, but if they are not a sequential subset of the index
> segments (a,b is valid, a,c is not, nor is b,c), PowerHouse 
> will ignore the
> VIAINDEX specification in the more recent versions (PH 
> 8.1...). (I'm not
> sure how accurate the comparison is for earlier versions.) 
> You can also
> override the ordering by specifying it.  In this case 
> PowerHouse will use
> the VIAINDEX segments but apply your specified ordering.
> 
> Hope this helps
> 
> Allison Hamilton
> My words and ideas are not necessarily my employers.

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Subscribe: "subscribe powerh-l" in message body to majordomo@lists.swau.edu
Unsubscribe: "unsubscribe powerh-l" in message to majordomo@lists.swau.edu
powerh-l@lists.swau.edu is gatewayed one-way to bit.listserv.powerh-l
This list is closed, thus to post to the list, you must be a subscriber.