The same batch retrieval-only program issuing the exact same DML run under CV shows a higher PAGES REQUESTED value than when run in local mode.
Lines Requested and Recs Made Current are identical.
Processing differs in CV due to considerations for other transactions that may be accessing the same pages.
- Under CV IDMSDBMS always releases its internal lock on a page at the
completion of a command to ensure that other run-units can access
the buffer. As a result a subsequent access to the same page is
passed to IDMSDBIO even though it may have been the last buffer (page)
accessed. This results in an increased PAGES REQUESTED value.
- For a local mode job there is no concern for conflicts with other
run-units so the internal buffer lock is not released until
another page is needed by IDMSDBMS. As a result an additional call to
DBIO is not required if we keep accessing the same database page. The
size of the difference depends on the data path characteristics of the
This means that the number of pages requested through CV will
typically be larger than the number of pages requested for a local job.
Whether a job uses dataspace or prefetch does not matter since the
statistic is updated by IDMSDBMS before control is passed to IDMSDBIO.