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More questions about Rushmore optimization
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De
25/06/1999 18:35:25
 
 
Information générale
Forum:
Visual FoxPro
Catégorie:
Base de données, Tables, Vues, Index et syntaxe SQL
Divers
Thread ID:
00234217
Message ID:
00234251
Vues:
26
>Hello Everybody
>
>I try to summarize all what I've read here and there about velocity in Data fetching and rushmore optimization. Some questions came into my mind after reading the interesting thread of last March about Deleted() tag and Rushmore optimization: I've picked some ideas that lead me to the following:
>
>Here is what I believe I have understood:
>
>If my (VFP)data are located on a server, each time I run a query through the LAN, I fetch all the records of all the tables involved in the SQL Select statement. Let's suppose there is only one 3MB table involved in the query: it would take about 3 seconds to fetch the table (on the idea that my ethernet LAN has a 10 KBits/sec speed): it's an eternity!
>
>In the same time, I read that rushmore optimization should be based on a local copy of these tables index files (March thread about Deleted() tags).
>
>If I understand right, I think that, compared to a non optimized query, a fully optimized SQL statement will:
>1- run against the local copy of the index file
>2- and then will only get the selected records from the distant table (or even only the desired fields), reducing both volume of repatriated data, trafic on the LAN and time of the query. This instead of fetching the whole distant table into my client station and processing the SELECTion on the local machine.
>
>In other words, does Rushmore optimization prevent to import the whole tables into the client machines each time a SELECT is run?
>
>Do I understand well?
>
>Selection processing is rarely clearly explained in guides or books, overall these subtleties about the way the data are fetched within or without Rushmore, about what exactly (whole tables? All records? Just some of them? All fields? Just some of them?just index tables?...)is repatriated when one runs a query.
>
>I hope to get useful answers to my questions and I'm sure that lots among us will be interesting in having the answers to these questions that remain vague to many.

FoxPro will attempt to cache the index locally. If it can't it will make successive calls to the server to get the needed pieces. Rushmore will try to use an existing index. If it determines that a suitable index does not exist (see my web page for more info), it may or may not create an index. It will try to determine if an index will speed up the query. If an index needs to be built, the entire table needs to be copied to the local workstation in order to create the index.
Craig Berntson
MCSD, Microsoft .Net MVP, Grape City Community Influencer
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