On Monday, 25 June 2012 06:16:57 UTC-4, foxy.md wrote:
>
> what I'm trying to avoid is segmentation violation when millions records
> are returned using EXECUTE "SELECT... WITH ..." RTNLIST ID.LIST in a routine
>
In many situations, you would be better off to avoid EXECUTE / SELECT /
RTNLIST entirely, and simply code the conditions for valid record
processing. By using an EXECUTE statement, then processing the resulting
list, you're reading every record twice, taking a hit on performance. Why
not read them just once by using the jBC SELECT statement? Example:
OPEN 'MYFILE' TO MY.FL ELSE ...
SELECT MY.FL
LOOP
READNEXT ID ELSE EXIT
READ REC FROM MY.FL, ID THEN
IF REC<5> = MY.VALUE THEN
DoSomething
END
END
REPEAT
While there is a performance benefit to this method, there is also a
caveat. The jBC SELECT statement does not scan the entire file to create a
full list of item IDs before processing begins. Instead, it just scans in
the first few IDs of the file. Once these IDs are taken from the list, a
few more are scanned until the entire file has been processed. A potential
"problem" with this, depending on your processing logic, is that you could
end up with records added to the file prior to when the SELECT was started.
--
Kevin Powick
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