Mainframe, MVS and zOS Discussion

hello,

I'm trying to understand how a control interval split occurs? When a CI is full with records, what happens when record with key 150 is inserted?

I searched it on google and there are references about VSAM demystified which I've downloaded but for novice like me it's tough to understand it. Can someone please assist me in understanding this concept about CI splits? And are they good or bad?

Your help is appreciated.

VSAM will access a free CI in the CA, move half the records from the full CI to the new CI, and then add the record being inserted. If there are no free CI in the CA, then VSAM will do a CA split and move half the CI to the new CA.

CI and CA splits used to be worse than they are now. As disks have gotten faster, the impact of CI splits has lessened. They are not really good, but neither are they bad any more -- if they get excessive, the VSAM file might be unloaded, deleted, defined, and reloaded but that typically is an application decision.