Data compression for monitoring records

CICS performs data compression, by default, on the SMF 110 monitoring records produced by the CICS monitoring facility (CMF). Data compression can provide a significant reduction in the volume of data written to SMF. The records are compressed and expanded using standard z/OS services.

Control data compression for monitoring records by specifying the COMPRESS option in your Monitoring Control Table (MCT), using the DFHMCT TYPE=INITIAL macro. COMPRESS=YES is the default for this option, meaning that data compression is used. If you specify the system initialization parameter MCT=NO, the default MCT built by CICS specifies COMPRESS=YES. If you do not want to compress monitoring records, you must specify COMPRESS=NO in your MCT.

You can inquire on and change the data compression option dynamically using the monitoring facility transaction CEMN, or the equivalent EXEC CICS commands. However, when CICS is restarted the data compression option reverts to the COMPRESS value in your MCT, if you use a monitoring control table and specify the monitoring control table suffix on the MCT system initialization parameter.

When data compression is active, CICS uses the standard z/OS Data Compression and Expansion Services (CSRCESRV) to compress the CICS data section of each monitoring record before writing it to SMF. The SMF header and SMF product section of records are not compressed. This process can provide a very considerable reduction in the volume of data written to SMF, and a corresponding reduction in I/O and CPU usage for the SMF address space. If you normally exclude monitoring data fields to reduce data volume, you might find that using data compression removes the need for exclusion and enables you to collect complete monitoring data.

The collected monitoring data can include a mix of compressed records and records that have not been compressed. Records might not be compressed because of the following situations:
  • Depending on the data pattern of the record, compressing the data section might possibly result in a larger record. If this situation occurs, CICS does not compress the record.
  • Data compression might fail because of a problem involving the z/OS Data Compression and Expansion Services.
  • Data compression might be switched off dynamically using the CEMN transaction or EXEC CICS SET MONITOR command.
When CICS SMF 110 monitoring records have been compressed, they must be identified and expanded using the z/OS Data Compression and Expansion Services, before they can be processed by SMF 110 reporting tools.
  • The CICS-supplied monitoring sample program DFH$MOLS supports the expansion of compressed CICS SMF 110 monitoring records. DFH$MOLS automatically identifies any compressed monitoring records in the input, and uses the z/OS data expansion service to expand them before working with them. If you specify the EXPAND control statement, DFH$MOLS copies the compressed monitoring records to an output data set in their expanded format, with the records that were never compressed. See Sample monitoring data print program for further information on the DFH$MOLS program.
  • If you use an SMF 110 reporting tool supplied by IBM or by another vendor, and you want to use data compression, make sure that the product can identify compressed CICS SMF 110 monitoring records and can expand the data section using the z/OS Data Compression and Expansion Services, so that the monitoring records can be processed correctly. If the reporting tool cannot work with records in this way, you might use DFH$MOLS with the EXPAND control statement to produce an output data set containing the SMF 110 monitoring records in their expanded format, for the tool to work with.
A reporting tool that is using the z/OS Data Compression and Expansion Services needs this information:
  • The field SMFMNCRL in the SMF product section of the record identifies where data compression has been used for a monitoring record and gives the compressed length of the CICS data section. A zero value for this field means that data compression was not performed on the record.
  • The maximum length of the CICS data section of an SMF 110 monitoring record, when expanded, is 32598 bytes.

For detailed information about the z/OS Data Compression and Expansion Services (CSRCESRV), see the z/OS MVS Assembler Services Guide, and the z/OS MVS Assembler Services Reference ABE-HSP.

Data compression applies only to SMF 110 records written by CICS monitoring, with subtype X'0001' in the record subtype field in the SMF header. It does not apply to the other types of SMF 110 records created by CICS; that is, records written by CICS journaling, CICS statistics, the TS data sharing server, the coupling facility data table (CFDT) server, and the named counter sequence number server.