Is the block size or CI size appropriate?

As a rule of thumb, use a 4 KB CI/block size for the data portion of a HIDAM. However, if the average database record length is more than 1000 bytes (that is, larger than 1/4th of the block or CI size), then an increase of the block or CI size from 4 KB to 8 KB might improve the performance of HIDAM database accesses.

In these cases, an increase of the CI size/block size from 4 KB to 8 KB can often reduce the number of I/O operations (but will increase slightly the time of an I/O operation). CI/block sizes larger than 8 KB should be an exception (for example, for very large average database record sizes).

Discussion of the example

You can check the current block size or CI size, the number of blocks or the number of CIs in the Data Set Statistics report. You can check the average database record size in AVERAGE DATABASE RECORD SIZE in the Distribution of Database Record Sizes report. In Figure 3, AVERAGE DATABASE RECORD SIZE shows 2,317 bytes. Because this is over 1000 bytes, you can expect performance to improve by increasing the block size from 4 KB to 8 KB.