This post is more than 5 years old
24 Posts
0
413
A recent customer issue: my vsam file took many CI and CA Splits. Why?
The customer was using Performance Essential (PSP) to buffer the program using LSR and thought that PSP might be the problem as without PSP the excessive CI and CA splits did not occur. Turns out the customer had forced SIS to be enabled and neither LSR nor NSR had anything to do with the issue.
What is SIS? SIS is Sequential Insert Strategy. IBM has two record insert strategies for VSAM datasets, NIS (Normal Insert Strategy) and SIS. IBM did this because inserted records can fall into two categories. The first category is randomly distributed inserts. This type of insert occurs most often, so IBM made the insert strategy which provides the best use of storage and the best performance for this category the default. That is NIS. The second category is clustered inserts. This type of insert requires a different strategy to maximize use of storage and receive good performance. That is SIS.
It turns out that using the wrong strategy for the type of insert pattern (NIS for clustered inserts or SIS for random inserts) causes poor storage use and poor performance.
Please refer to http://csgateway.emc.com/primus.asp?id=emc217779 for more information on NIS and SIS.
Please refer to http://csgateway.emc.com/primus.asp?id=emc166727 for more information on when SIS should be used.
What is SIS? SIS is Sequential Insert Strategy. IBM has two record insert strategies for VSAM datasets, NIS (Normal Insert Strategy) and SIS. IBM did this because inserted records can fall into two categories. The first category is randomly distributed inserts. This type of insert occurs most often, so IBM made the insert strategy which provides the best use of storage and the best performance for this category the default. That is NIS. The second category is clustered inserts. This type of insert requires a different strategy to maximize use of storage and receive good performance. That is SIS.
It turns out that using the wrong strategy for the type of insert pattern (NIS for clustered inserts or SIS for random inserts) causes poor storage use and poor performance.
Please refer to http://csgateway.emc.com/primus.asp?id=emc217779 for more information on NIS and SIS.
Please refer to http://csgateway.emc.com/primus.asp?id=emc166727 for more information on when SIS should be used.
Davidy8s
154 Posts
0
July 2nd, 2009 06:00
I think the overall conclusion here is that loading VSAM data sets with the "less than optimum" insert strategy is necessarily going to produce more CI / CA splits; regardless of whether or not you're using Performance Essential.
Dave Yates
EMC TSE3
Benevolent Host S/W & Mainframe Forum Moderator
Il Moderatore Benevolo
2 Attachments
PSPV62C.results.TXT
PSPV62A.results.TXT