IBM Mainframe Forum

[ewansyo]

How does the CI SIZE affect the ESDS VSAM file in terms of processing speed? Does larger CI SIZE much faster?

[c62ap90]

I always start define as CISZ (4096) and then depending on, for example, Splits - I contact our Systems Programmer for VSAM file tuning.

Some more info...
http://pic.dhe.ibm.com/infocenter/pdthe ... pvsm51.htm

An average CISZ of 4K is suitable for most applications. A smaller CISZ means faster retrieval for random processing at the expense of inserts (that is, more CISZ splits and therefore more space in the data set). A larger CISZ results in the transfer of more data across the channel for each READ. This is more efficient for sequential processing, similar to a large OS BLKSIZE.

[Robert Sample]

For an ESDS, I'd probably go with 18432 which is most space-efficient. However, if the application is running under CICS 4096 might work better as there is less data written at a time. If the application is running only batch ESDS with no alternate indexes, then 32768 might be your best CI SIZE. There is no one "true" answer to a question like yours -- it depends upon the site, whether the ESDS file has alternate indexes, whether the ESDS file is used online only or batch only or both, and other factors.

[ewansyo]

Hi,

Thank you both for the helpful responses.

The ESDS file has no alternate index and will be used only as an online log, we would only do write to this file. So does it mean that 32768 might be good for this type of file?

[NicC]

If the application is running only batch ESDS with no alternate indexes, then 32768 might be your best CI SIZE.

[Robert Sample]

For an online log, 4096 is probably your best choice. You want logs to be written fairly quickly, and hence a smaller CI SIZE makes sense.