Sort performance

One of the biggest factors that influences elapsed time is sorting log data, index keys, or both. NGT Recover offers many options that enable you to control the efficiency of the sort and customize the sort based on your environment.

Multiple concurrent key sorts provide the greatest performance gain for the product. For each table space, NGT Recover distributes the index keys for all indexes being rebuilt over a user-defined number of sorts and runs these sorts in parallel. For a partitioned table space, if the partitioning index is being rebuilt, NGT Recover does the rebuild of each partition at the completion of the MERGE or UNLOAD for each partition of the table space and this may happen concurrently with the MERGE or UNLOAD for the next partition (if the user-specified number of sorts is not exceeded).

When NGT Recover has input all of the keys to the sort for a group of indexes, NGT Recover then performs the REBUILD operation for each index in a subtask. There could be one subtask for each group of indexes that were sorted in the previous MERGE or UNLOAD phases. So, index REBUILDs can run concurrently.

NGT Recover determines the number of concurrent REBUILDs for each table space during analysis but never exceeds the user-specified number of sorts. Once NGT Recover schedules all of the REBUILDs for a table space in multiple subtasks, it begins the next MERGE or UNLOAD for a different table space if the user-specified number of sorts will not be exceeded.

NGT Recover uses BMC BMCSORT technology for sorts. This technology provides NGT Recover with more control of the sort process than external sort routines provide. This added control helps prevent memory-related problems during the sort process.

NGT Recover allocates the amount of resources to each sort process based on the amount of work that NGT Recover determines that the sort process will perform. NGT Recover also dynamically detects excess available memory and allocates a percentage of them to the sort processes.

The following areas are of major importance to sort performance and can be customized:

• Number of parallel sorts allowed

• Central and expanded storage

• DASD work space

In general, the more central and expanded storage available to the sort, the better the sort performs. In most cases, the NGT Recover and sort installation default values are sufficient, but if the defaults are not appropriate for your needs, you can use NGT Recover options to override them.

This section contains the following topics:

• Recommendations for a large number of concurrent sorts
• Sort file size estimation
• NGT Recover sort parameters
• Allocation of sort work space