RE: Can a Query fill the system?

[Gord Royle <GRoyle@xxxxxxxx>]

The culprit may very well be a join that creates a "cartesian" results set.
Suppose you have two tables each with 1,000,000 records. If the join is not
done properly, you can select the first record from tableA and join it to
the 1,000,000 records from tableB then select the next record from tableA
and join it to the same 1,000,000 records from tableB. The ultimate result
is a results set with 1,000,000 X 1,000,000 records in it.

Gord Royle

-----Original Message-----
From: pam@medisense.com [mailto:pam@medisense.com]
Sent: Wednesday, October 02, 2002 9:57 AM
To: midrange-l@midrange.com
Subject: Can a Query fill the system?



I'm running a Model 720 with 400 GB, which is usually about 75% full. Last
night, it suddenly went to 90%. When I dialled in to check it, the only
suspicious job I could find was a query that had been running for over three
hours and still hadn't created output. So I killed it, and like magic, I was
back at 75%.

Now that I've had a chance to look at yesterday's performance graphs, I find
that three times, this query and similar ones filled the disk to the
threshhold in the course of two hours. These queries link four files, one of
which is huge. Clearly, there's something wrong with the joins. I've seen
this
sort of thing cause queries to run for ages to no effect, but I've never
seen
them chew up disk space like that.

What could it be doing that would fill 60GB in 2 hours?

Pam Phillips


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