DB2 for z/OS Coupling Facility Sizing

Just a very brief blog post today to inform you about something that I ran across doing some web research today... and that is a free, web-based Coupling Facility sizing tool from IBM named CFSIZER. 

The CFSIZER tool will connect to your live server to get information. You will need to input some values and some estimation of the type of workload for your system and CFSIZER will output its recommendations.

If you are struggling with your Data Sharing environment this might be a good place to start if you don't have any tools to help you. Here is the link to CFSIZER.

Thanks IBM!

The Db2 12 for z/OS Blog Series - Part 16: Db2 Catalog Availability Improvements

IBM has improved the availability of accessing Db2 Catalog objects when maintenance is being run in Db2 12 for z/OS. This impacts access during CATMAINT and online REORG.

This change is largely being driven by dynamic SQL, which is more prevalent but can cause problems. When dynamic SQL statement is executed, Db2 must dynamically prepares the SQL to determine access paths in order to run it. During this dynamic SQL preparation process, Db2 acquires read claims on a handful of Db2 Catalog table spaces and their related indexes. Additionally, a DBD lock is acquired on the Db2 Catalog database. The DBD lock is needed to serialize catalog operations with CATMAINT and other DDL that may execute against the catalog, because CATMAINT might be making structural changes to the catalog.

Prior to Version 12, the DBD lock and the read claims were released at COMMIT points. All well and good, but for transactions issuing dynamic SQL but not committing frequently, CATMAINT and online REORG on the Db2 Catalog were blocked during that period period of time.

As of Db2 12, DBD locks on the Db2 Catalog and read claims against catalog objects are released as soon as PREPARE statement execution is complete. This will improve availability for CATMAINT and online REORG of Db2 Catalog objects.

The Db2 12 for z/OS Blog Series - Part 15: DSN1COPY and Data Validation Improvements

If you’ve worked with Db2 for z/OS for awhile (note to IBM: I still have a problem with that lower case "b" but I'm trying), particularly as a DBA, you’ve almost certainly had the opportunity to use the DSN1COPY offline utility, sometimes called the Offline Copy utility.

DSN1COPY can be used in many helpful ways. For example, it can be used to copy data sets or check the validity of table space and index pages. Another use is to translate Db2 object identifiers for the migration of objects between Db2 subsystems or to recover data from accidentally dropped objects. DSN1COPY also can print hexadecimal dumps of Db2 table space and index data sets.

Its primary function, however, is to copy data sets. DSN1COPY can be used to copy VSAM data sets to sequential data sets, and vice versa. It also can copy VSAM data sets to other VSAM data sets and can copy sequential data sets to other sequential data sets. As such, DSN1COPY can be used to

• Create a sequential data set copy of a Db2 table space or index data set.
• Create a sequential data set copy of another sequential data set copy produced by DSN1COPY.
• Create a sequential data set copy of an image copy data set produced using the Db2 COPY utility, except for segmented table spaces. (The DB2 COPY utility skips empty pages, thereby rendering the image copy data set incompatible with DSN1COPY.)
• Restore a Db2 table space or index using a sequential data set produced by DSN1COPY.
• Restore a Db2 table space using a full image copy data set produced using the Db2 COPY utility.
• Move Db2 data sets from one disk to another.
• Move a Db2 table space or index space from a smaller data set to a larger data set to eliminate extents. Or move a Db2 table space or index space from a larger data set to a smaller data set to eliminate wasted space.

Given such a wide array of useful purposes you can see how DSN1COPY is an important arrow in a DBA’s quiver… But remember, it is an offline utility, so Db2 is not aware of – or in control of the data that is moving. So if you use it to change data in a production page set data integrity issues can arise. For example, you may get mismatches between the data page format and the description of the format in the Db2 Catalog.

Other types of errors that can ensue when using DSN1COPY include:

• incorrect DBID/PSID/OBID values,
• improper table space layout (for example, using DSN1COPY to copy data from a segmented table space to a partition-by-growth universal table 
• version number and table definition errors

In scenarios where DSN1COPY was not used properly you can encounter invalid data, abends, and storage overlays. Not good!

Thankfully, we get some help in Db2 12 for z/OS though. Improvements to the REPAIR utility make it easier to detect and correct data mismatches. You can use the REPAIR CATALOG utility to fix situations where the column data type or length in the table space differs from the catalog definition for the column. If Db2 can convert from the data type and length in the table space to the data type and length in the column then the REPAIR CATALOG utility enables conversion. The data type or length of the data in the table space will be changed to match the definition in the Db2 Catalog the next time that the data is accessed.

Additionally, we can use the REPAIR CATALOG TEST utility to detect multiple types of data mismatches. All of the following can be detected:

• If a range-partitioned table space indicates absolute page numbering, but the catalog indicates relative page numbering; and vice versa.
• The number of columns in the table space is greater than the number of columns in the catalog definition of the table.
• The column data type or length in the table space differs from the catalog definition for the column.

So Db2 12 makes life a bit easier for those of us who use DSN1COPY and sometimes do not specify the parameters or the data sets exactly perfectly.