RE: issues explaining performance issues to clients
- From: "Julio C. Aguilar-Chang" <jachang@xxxxxxxx>
- To: ganstadba@xxxxxxxxxxx
- Date: Wed, 22 Jul 2009 23:00:08 -0600 (MDT)
I'm glad to see that I'm not the only one with this problem!! I support a
database that is used as a data warehouse to conduct geophysical research.
The largest tables we have in the schema that holds the "raw" data that
the researchers use are in the order of 150 million rows. All the
researchers connect to the database using SQLPlus, each connects to their
own schema and, just like you, are free to issue any sql query they can
come up with in order to retrieve the data that they will be using for
their research.
Once in a while I get a phone call from one of them telling me that the
query is taking too long. The very first thing I ask and seems to work
for me and solve the problem immediately is: "How many times are you
going to run this query that is taking a long time? If you are going to
run it once or twice, then just let it finish because it is really not a
good use of my time to spend hours troubleshooting one query that will
only be run once or twice". Usually they realize that this makes more
sense and go away.
Unfortunately there is only so much we can do about this. The best that I
can hope for is to tune the system as a whole, and pretty much give up
tuning sql queries because 95% of the time these queries will only be run
once or twice.
Of course I always take a look at the current execution plan of queries
that are taking too long according to the researchers, and once in a while
I do find a query with 3 or 4 table joins and not enough join conditions
or obvious missing indexes.
Hope this gives you some comfort ... you are not alone!
Email: jachang@xxxxxxxx
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