Advantages

• BMC AMI Fast Path Indexer for IMS provides index building and maintenance capabilities for DEDBs.
• In a manner similar to how secondary indexes work with IMS full-function databases, an index to a Fast Path DEDB lets your applications process the primary DEDB in an alternate processing sequence.
• Because the index contains only a portion of the data in the primary DEDB, processing time is reduced for scan or browse operations.
• Using an index increases transaction throughput.
• BMC AMI Fast Path Indexer for IMS uses IMS services to update the index automatically when changes are made to the primary DEDB.
• You can use standard IMS services to recover an index to the same point in time as the primary DEDB.
• You can rebuild an index from the recovered primary DEDB by using the product’s batch utilities.

Enables creation of indexes

In efficient database designs, segments and fields are arranged to best fit the requirements of the most frequently used transactions.

Even the most well-designed database, however, can run more efficiently if it enables applications to use an alternate processing sequence when needed. A secondary index database solves this dilemma; you can use a second (alternate) processing sequence for the same database without disrupting the primary processing sequence that is defined in the primary DEDB.

The following figure shows an example of a primary DEDB and an associated secondary index database. The primary DEDB accesses course data through the root segment (Course).

Database structure for primary DEDB and secondary index databases

For an application to access this primary DEDB, the application must know the course number (root segment) before accessing any other information. If you use an index, however, the entry key into the database can be any segment; it does not have to be the root segment.

For example, assume that your application program could benefit by accessing the database through the Location segment, not the root segment (Course). Using a secondary index database, the application program accesses the database in this alternate manner. The application program accesses the database directly at the Location segment by using the Location code as the key. The program can then access all dependent segments of Location.

Path calls enable the application program to retrieve any segment in the path from the source segment (Location) to the root segment (Course). After the application accesses the Location segment, the segment is placed into the application’s I/O area. This type of access speeds processing time by reducing the number of times that the application must access the primary DEDB.

Improves integrity

BMC AMI Fast Path Indexer for IMS addresses the following integrity issues:

• primary DEDB maintenance

  BMC AMI Fast Path Indexer for IMS does not alter or interfere with the primary DEDB.

• index maintenance

  BMC AMI Fast Path Indexer for IMS uses IMS services to provide index maintenance when changes are made to the primary DEDB. To ensure integrity, BMC AMI Fast Path Indexer for IMS prohibits the application from updating the index directly.

• recovery

  BMC AMI Fast Path Indexer for IMS lets you register an index with the IMS Database Recovery Control (DBRC) feature. If you need to recover the primary DEDB, you must perform a synchronous recovery of the index and the primary DEDB. You can recover the index to the same point in time as the primary DEDB, or you can rebuild the index from the recovered primary DEDB by executing the BMC AMI Fast Path Indexer for IMS BUILD command.

Enables selective duplication of source data

Creating an index by using BMC AMI Fast Path Indexer for IMS is an efficient way to duplicate data from a primary DEDB.

If you process your index as a stand-alone database, you can create commands that duplicate only specific data from the primary DEDB. This capability lets you process only the index for that data. Otherwise, you would have to process the entire primary DEDB, which would be time-consuming and costly.

Enables concurrent index rebuild during change or reload

If you change the primary DEDB, you can simultaneously rebuild the associated secondary index database via the offline CHANGE or RELOAD commands; these commands are available in the Fast Path Reorg/EP product.

Offers choice of index structure

When defining BMC AMI Fast Path Indexer for IMS indexes, you can use a SHISAM structure or HISAM structure. Both of these database structures store the index data in sequential order.

Consider the following items based on index activity:

• SHISAM does not reuse the space for deleted segments.
• HISAM reuses space from deleted segments. HISAM is a better choice for high-activity indexes.

Enables concurrent initialization of source and indexes

If you are initializing a DEDB that has registered indexes of the DEDB structure type, BMC AMI Fast Path Indexer for IMS lets you simultaneously initialize the primary DEDB and its indexes in one job step.

You can initialize the primary DEDB and indexes when executing the INITIALIZE command that is available in the Fast Path Reorg/EP product.