Re:Maximum Page Size for IDMS Database Files

Discussion created by ca.portal.admin on Jul 18, 2006


We look as though we will be running on new disks in the future that
would be formatted as 'MOD 9' rather than our current '3390' style. This
would allow us to increase our page sizes for the IDMS files. We are
running 16.0 SP1 and the manual suggests that 32764 is the maximum
allowed by IDMS. Is this true or could we go bigger if warranted?




Chris Wood

Alberta Department of Energy


2006-07-18, 11:37:57
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IDMS Public Discussion Forum


Re: Maximum Page Size for IDMS Database Files
"Dusting off the cobwebs from my brain I seem to remember that the 32K restriction was in the I/O subsystem. When an access method, like BDAM or QSAM, built EXCP commands the op codes, address, flag bytes and byte count were placed into a channel command word (CCW) which was actually two words long. In the original (format-0) version the data address was limited to 24 bytes so all I/O was placed below he line. Later in the format-1 version of the CCW the address field was opened up to 31 bits so I/O could go directly above the line. However, in both formats the byte count field would only support 32k.

I believe (but not positive) that there is now a format-2 CCW which can obtain a larger byte count. So if the hardware device supports larger blocks, the access method has been updated to use the format-2 CCWs, and the IDMS internal software and control blocks can support the larger pages; then you should be good to go. But that is a few ifs.

Bill Boyce
GE Money