IDMS Journal buffer SPLIT count

Products

• IDMS - Database

Issue/Introduction

The IDMS DCMT D BUFFER command shows a non-zero SPLIT count.

Does that mean that the journal page size is too small?

Environment

Release: All supported releases.

Resolution

The documentation indicates the SPLIT count  means - Number of times I/O was forced to avoid a small split journal record.

The journal buffers can contain multiple records. A SPLIT does not necessarily mean that the buffer is too small. It means the journal record doesn't fit into the current buffer. So IDMS forces a write on the current buffer and puts the record in a new buffer.

Whether the journal buffer is too small or not depends on the size of the records in the database.

See the documentation on journal buffer sizing which has some recommendations:

Buffer Page Size
The journal buffer page size determines the block size for the disk or tape journal files that are specified for the DMCL. Use the following criteria to select a size for the journal buffer pages:

• If possible, the page size should be at least twice the size of the longest database record occurrence
• The page size should approximate an optimal page size for the device type in which non-VSAM disk journal files reside.