06101528.txt 10-Jun-00


Subject: Problem with network performance
From: dark@dark.com (Dark Agony)

My program accesses my .dbf files on a mapped drive. When I
  create a report, I lose a lot of performance when i'm
  using the SET FILER TO.
any ideas ?

Subject: Re: Problem with network performance
From: "Bob Predaina" <Clipper@custombasses.nospam.com>

as you probably know, accessing a database using SET FILTER
  TO is very slow compared to indexing.  With the SET FILTER
  command, behind the scenes clipper still process every
  record in the database, whether it meets the filter
  condition or not.  this is not the case with indices.  as
  a result, you're making many more disk accesses than you
  would have to make if you were using the INDEX condition.
when using the INDEX method on a local disk, much of the
  data that you're attempting to access is likely to be
  found in a cache or a buffer.  when using the SET FILTER
  condition, this may be less likely to be the case.
accessing the data over a network adds a number of layers of
  processing to the data acquisition relative to keeping the
  data online on the same PC.
you have to 1) request it on the machine that is hosting the
  app, 2) convert this request for data to a network access
  command, 3) perform a disk search on the network drive, 4)
  transmit the results back over the network, and 5) process
  the network packet on the host once it arrives.  this
  amounts to a predictable degradation in performance.
to minimize the problem, you best bet would be to create a
  few extra indices and use them instead of SET FILTER.  if
  you could move them and your database to a local drive,
  all the better.

HTH.
Bob Predaina