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Performance suggestions for a large table
Message
Information générale
Forum:
Visual FoxPro
Catégorie:
Codage, syntaxe et commandes
Divers
Thread ID:
00239591
Message ID:
00239668
Vues:
19
If you're selecting records by RECNO(), I would use GO and COPY TO ARRAY. Try this for getting 100 records starting with record 700,000:
GO 700000
COPY NEXT 100 TO ARRAY laMyArray
>I have a 1 million row table with a primary key of RECNO(). I need to pull random sets of 100 contiguous rows from the table. I have tried 3 things:
>
>1) SELECT * FROM table WHERE PriKey>=N AND PriKey>2) SEEK followed by COPY TO ARRAY
>3) SEEK followed by SCAN
>
>All three get a throughput of about 10 requests per second. This seems slow to me. Would anyone disagree? Can you suggest a better way to do the requests?
>
>Especially in the SCAN case I am puzzled. It would seem that all FoxPro has to do is read the records sequentially (I tried using SET ORDER TO 0 and NOOPTIMIZE), yet my disk's average transfer rate is 5 times the result set size and my CPU is at 15%.
>
>Also, in the SELECT case, I am collecting statistics and I see some requests taking 10 milliseconds and others taking 450 milliseconds. Based on the ranges requested, it does not look like buffering is causing the speedy ones so could disk fragmentation be causing the slow ones?
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