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The LA
Fox
Developer Newsletter
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June
1994
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The LA Fox Developer
is the monthly newsletter of the LA Fox User Group. The purpose is information sharing among application developers and users working with
FoxPm.
LA
Fox
Address:
LA
Fox User Group
977 Ashbndge Lane
Harbor City, CA 90710
LA Fox Board of Directors
Chuck Williams, President
David Van Valkenburg, Treasurer
Allen Garfein, Membership
George Dvorak
Warren Rekow
Bill Seldon
Barry Lee, Newsletter Editor
Gregg Dunn
Kns Dahlin
The newsletter contains regular columns and articles from other user groups.
XPro User Group
2210 Wilshire Blvd.
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#161
Santa Monica, CA 90403
OC FoxPro Developers Group
Subscriptions
The annual membership fee for the LA Fox
User Group, including subscription to
The LA
Fox Developer Newsletter,
is $45.
Disclaimer
Neither the LA Fox User Group, the XPro User Group, the OC MS FoxPro Developers Group, their officers or board of directors or their members make any express or implied warranties of any kind with regard to any information disseminated, including, but not limited to, warranties of merchantability and/or fitness for a particular purpose.
Opinions provided by newsletter articles, or by speakers, members, or guests who address the meetings, are individual opinions only, and do not necessarily represent the opinions of the group. All opinions and information should be carefully considered, and the group is not liable for any incident or consequential damages in connection with, or arising out of, the furnishing or use of any information or opinions. Brand names and product names may be trademarks or registered trademarks of their respective owners.
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LA Fox President’s Column
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situations.
And FoxPro is at the forefront of this advance, with its Rushmore query optimization technology, which was the focus for most of this meeting. Rushmore operates with commands that include a For clause containing an optimizable expression, with files operating under Set Filter conditions, and with SQL Select queries containing optimizable expressions in the Where clause. The amount of performance improvement depends largely on the relative size of the result set to the whole file, and the relation of the query expression to the expressions for the available indexes.
Despite the fact that Rushmore is “fully integrated and automatic”, it really does require careful design and careful programming to get the full benefit, or at least to stay out of the way and let FoxPro do its thing. There are no hard and fast rules that work in every situation, but there are guidelines that will steer you in the right direction in laying out your data structure, building indexes, and expressing queries. If performance is really critical, there is no substitute for carefully designed testing to evaluate alternatives in your particular data and network environment. As usual in complex situations, there are tradeoffs
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you may have to program for best response for one type of query at the expense of slower response for other queries
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picking the right strategy depends on knowing your data and knowing your queries.
Perry led us through a range of topics including the Append From command for speed when adding records to a file, the importance of exactly matching the For clause expression to an index expression, the benefits of even partial optimization, the need to build an index tag on the Deleted() function, the need to avoid setting an Order, the benefits of Selecting into a cursor, and many more. Needless to say, this brief column can’t do justice to the topic, but I can point you at some other sources if you want more information.
Much of the material we covered, including some of the same examples, is included in George Goley’s book, Creating FoxPro Applications. George devotes 22 pages in Chapter 15 to a discussion of Rushmore and performance issues. This is a long time area of specialization for George
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he has written many articles in Data Based Advisor and he speaks on this topic at every FoxPro devcon
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you won’t find it more thoroughly or clearly described. However, this is a complex topic, and no single approach works for everyone, so you might want to look at David Kalman’s book, FoxPro 2.5 Developers Handbook. David devotes 60 pages in Chapter 6 to Rushmore and SQL, and part of Chapter 3 to indexing strategies (combination of
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