COBOL technology has a group of rules, known as COBOL DB2 rules, that provide quite accurate insights on performance and efficiency issues related to DB2 access.
They have been proven to find performance issues and to provide remediation clues.
You can find COBOL DB2 rules in Models Management - Rules, and filtering by language = cobol and tag = repository.
Configuration of COBOL DB2 rules
To properly work, COBOL DB2 rules need to be fed with DB2 information.
All together, the DB2 information and the rules' logic provide quite a powerful performance issues detection system.
Their rules consume DB2 information from two specific resource files (catalog and plantable files).
These resource files are tightly coupled to your DB2 installation so you should provide them so Kiuwan can apply its efficiency logic.
Below you can find the way to specify location and format of these files.
Regarding format, every file follows a specific (fixed) sequence of information fields with a default size.
You can modify default sizes but keep always the order, as the rules will read those files according to the specified sequence.
DB2 Catalog file
This file contains information related to tables being used by the program to be analyzed. In case the program does not access DB2, this file will be empty.
Information contained in this file is organized by table and for every table is divided into three sections:
- Table Line format (one record per table, 37 characters)
- Indexes Line format (one record per index and table, 20 characters)
- Index Fields Line format (one record per field of the index, 24 characters, and records ordered according to the order that appears in the index)
There are two properties defined in ${kiuwan_local_analyzer_installation_dir}/conf/analyzer.properties file to configure DB2 Catalog file:
- cobol.db2.catalog.path
- cobol.db2.catalog.format
cobol.db2.catalog.path
This property defines where the DB2 catalog file is located.
After the 'file:///' prefix, encode the path where to find the resource files.
You can define an absolute path or a relative one. Use the '@{src.dir}' pattern to set a path relative to the source directory of the analysis.
cobol.db2.catalog.path=file:///@{src.dir}/resources/catalog.txtcobol.db2.catalog.format
This property is used to define the inner format of Catalog file.
# Format definition for Catalog resource.
cobol.db2.catalog.format=2:18_20:9_29:9_2:18_20:(1)_21:9_30:9_2:18_20:5Source program file and Catalog file
There is a correspondence between DB2 table INCLUDES specified in the source program file and the tables contained in Catalog file.
When this correspondence does not exist is because a VIEW is being used. In that case, tables used are located at PlanTable file and those tables found there are those to be searched in Catalog file.
Also, although is not a good practice, it’s not mandatory to INCLUDE a used table if its host variables will not be referenced. In this case, above mentioned correspondence will not exist.
DB2 Plan Table file
This file contains performance information related to DB2 accesses into the program to be analyzed.
For each access, this file contains one or more lines, and all of them belonging to the same access will have the same value in QUERYNO field.
In case the program does not access DB2, this file will be empty.
Every record is 168 characters long according to a specific format.
There are two properties defined in ${kiuwan_local_analyzer_installation_dir}/conf/analyzer.properties file to configure DB2 Plan Table file:
- cobol.db2.plantable.path
- cobol.db2.plantable.format
For specific information on DB2 performance aspects and EXPLAIN tables, please visit IBM related documentation pages as the following:
http://www.ibm.com/support/knowledgecenter/SSEPEK_10.0.0/perf/src/tpc/db2z_createexplaintables.html
cobol.db2.plantable.path
This property defines where the DB2 PlanTable file is located. It has the same syntax as catalog file path.
An example of configuration could be:
cobol.db2.plantable.path=file:///@{src.dir}/resources/plantable.txtcobol.db2.plantable.format
This property is used to define the inner format of PlanTable file.
You have to encode the position and length (separated by ':' character) of each one of the required fields in the file. To separate each pair position:length, use the '_' character.
Take notice that there are some lengths defined between parenthesis, that means that those lengths can not be changed.
Check following examples and graphics to understand the required fields meaning and how to encode them in the property.
# Format definition for PlanTable resource.
cobol.db2.plantable.format=1:9_10:4_14:8_22:8_30:4_34:4_38:8_46:18_64:4_68:2_70:4_74:8_82:18_100:(1)_101:(1)_102:(1)_103:(1)_104:(1)_105:(1)_106:(1)_107:(1)_108:(1)_109:3_112:(1)_113:(1)_114:4_118:(1)_119:6_125:26_151:18Source program file and Plan Table file
There is a relationship between DB2 accesses in the source program file and the information contained in PlanTable about performance for all of them.
Rows in PlanTable are grouped by AX_QUERYNO field, meaning they correspond to the same DB2 access. Rows order in PlanTable matches DB2 accesses order in the program source file. Every SELECT, UPDATE, DELETE, INSER or CURSOR declaration should be contained in PlanTable file.
The relationship between DB2 accesses (access-type objects) from source program and corresponding rows in PlanTable file is M:N according to the following table:
Considering 1:N as number of rows in PlanTable for one access.
| Access Type | Access-type Objects | Relationship |
| Simple | 1,being N the number of wos in PlanTable | 1 – 1:N |
| With SUBSELECT | M, being M-1 the number of subselects | M - N |
| With UNION | M, being N the number of selects participating in the UNION | M - N |
| INSERT /SELECT | 2, one for INSERT y one for SELECT | 2 - N |
Different combinations of the above table can be found depending on the access, i.e. an access with UNION and SUBSELECT will have as many access objects as SELECT in which can be decomposed. Rows identified with the same query do not match the total.