I'd like to mention a DASD feature: CACHE.
Frequently accessed data (i.e. VCR in VVDS) probably resides in cache,
so performance penalty is not so big.
--
Radoslaw Skorupka
Lodz, Poland
John H. Lang wrote:
The DFSMS: Managing Catalogs manual says:
quote
"The Effect of Sharing Catalogs on Cache Usage If a catalog is defined with
share options (3 4), and if it resides on a shared device, catalog
management considers the catalog a shared catalog. A catalog is considered a
shared catalog if it meets both of these conditions, even if it is not
actually being shared among systems. Before each physical access to a shared
catalog, special checking is performed to ensure that the ISC or CDSC
contains current information. Checking also ensures that the access method
control blocks for the catalog are updated in the event the catalog has been
extended, or otherwise altered from another system. This checking maintains
data integrity. It also affects performance because the VVR for a shared
catalog must be read before using the ISC or CDSC version of the BCS record.
Recommendation: To avoid catalog corruption, define a catalog volume on a
shared UCB and set catalog share options to (3 4) on all systems sharing a
catalog."
unquote
John Lang
Central Coast Software
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