I've got a SQL Server 2000 database serving a classic ASP web
application. The performance of the database keeps nosediving and I
can't figure out why.

When preforming normally, running a known query will return a result set
in 5 seconds. After time, or more commonly after a big data import (the
system allows import from CSV files), the query can take more than 20
seconds to return the same data.

If I go and manually clean out all the data from the import (so the
tables have the same numbers of rows as before) the query will still run
at >20secs. I've also tried rebuilding the indexes and defragmenting the
data disk, and running the maintenance tasks to compact the log files.
Performance remains in the 'sucks' region.

However, if I detach the database and immediately reattach it,
everything perks up and the query runs in 5 seconds again.

I'm not entirely sure what happens during the detach/attach process.
Does anyone here have any ideas as to what might be fixing the issue
(and therefore any clues to the cause)?

thanks,

[quoted text, click to view]

Yes, auto update and auto create are both enabled. Something someone
suggested I try is manually updating the statistics when it's running
slowly.

So as soon as it does it again, I'll try that. Any other suggestions
welcomed!

Is the auto update statistics option enabled ??? It sounds like the
database creates statistics when you attch the database, but don't
update them