Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!rpi!uupsi!cai.com!setas01
From: setas01@cai.com
Newsgroups: comp.databases
Subject: Re: SQL Precompilers
Message-ID: <324.26c7e25e@cai.com>
Date: 14 Aug 90 11:37:02 GMT
Organization: Computer Associates International
Lines: 28

Subject : SQL pre-compilers. 

Bruce E. Golightly   from  bg0l@andrew.cmu.edu (BeeGeeZeroEl) writes : 

>I'm not sure that you'd like the kind of pre-optimization you described. If the
>characteristics of the data base changed to any real extent, performance
>could fall right through the floor. Good performance can be related to 
>optimization that makes use of statistics on the data base AS IT PRESENTLY
>EXISTS. Old stats may be very misleading!!

I agree that old stats may be misleading, if the access plan is not
modified to reflect the changes done to the database. So  the access plans 
must change depending on the new stats. This is taken care of in CA-DB.
CA-DB provides a command to update statistics and invalidate all related 
queries. However, if there are changes in fields or indexes, all the compiled
queries accessing the tables are automatically invalidated. 

The invalidated queries are then re-compiled the next time any of the query
is executed. Thus, it automatically compiles before executing it and stores
the access plan for future use. The user need not have to manually do this.
CA-DB version 1.5 also provides a command to validate all compiled queries
that have been invalidated.  

This is the kind of pre-optimization supported by CA-DB from Computer
Associates, a relational DBMS available on VAX/VMS and UNIX environments.

Ashok Sethi                    UUCP      :     mit-eddie!usgcdh!setas01    
			       INTERNET	 :     USGCDH!setas01@eddie.mit.edu