"Stevenson, Charles" <[EMAIL PROTECTED]> wrote:
<snips>
Which would you suppose is much faster:
...
FOR I = 1 TO 100
EXECUTE 'SELECT VOC WITH TYPE = "V" COUNT.SUP'
LOOP WHILE READNEXT ID
NULL ;* GOSUB DO.STUFF
REPEAT
NEXT I
...
or
...
OPEN 'VOC' TO F ELSE STOP
FOR I = 1 TO 100
SELECT F
LOOP WHILE READNEXT ID
READ REC FROM F, ID THEN
IF REC[1,1]='V' THEN
NULL ;* GOSUB DO.STUFF
END
END
REPEAT
...
Notice how much less work #2 (seemingly) does:
...
Method 2 takes 2 or 3 times as longer to run than Method 1. It's not
because VOC is a special file.
I've tried it on other files, big and small.
...
</snips>
It is my understanding that UniData (at least...don't know about UniVerse)
cache's the SELECT in Method 1. You can see this from ECL by timing a huge
select, then CLEARSELECT, then re-issue the original select. The second
run will come back much quicker.
Also, Method 2 reads the block from the file and reallocates the value of
"REC" for each iteration, while Method 1 reads each block once and parses
for ID's. Assuming 10-20 records per block (recommended file sizing from
my UniData Admin trainer), that's a 10- to 20-fold savings on disk reads.
--Tom Pellitieri
-------
u2-users mailing list
[EMAIL PROTECTED]
To unsubscribe please visit http://listserver.u2ug.org/
