The workflow system uses indexes to facilitate and speed up searches. When you create a roster, queue, or event log, Process Configuration Console automatically creates the indexes, marked with a system icon.
The indexes that the workflow system needs in order to function properly are indicated by the tooltip that appears when you hold the cursor over the icon. You cannot change or delete a mandatory system-defined index.
You can define indexes, depending on the needs of your system. You can add, change, or delete user-defined indexes on rosters, queues, and event logs.
By default, the workflow system creates an index for user queues called PWDefaultOrder. This index determines the order in which a user's work appears in his inbox. You can modify this index to change the default order.
Use additional indexes sparingly as they add to the system overhead, both in space and performance. Indexes are the primary means of reducing disk I/O when properly used. Retrieval performance of indexed data remains almost constant, even as new rows are inserted. However, the presence of many indexes on a table decreases the performance of updates, deletes, and inserts because the system must also update the indexes associated with the table.
You can create simple or composite indexes. A composite index (also called a concatenated index) is an index that you create on multiple columns in a table. Columns in a composite index can appear in any order. Composite indexes can speed retrieval of data for search filters in which the filter conditions reference all or the leading portion of the columns in the composite index. Therefore, the order of the columns used in the definition is important; generally, the most commonly accessed or most selective columns go first.
An index must not exceed the maximum index key size.
Some system indexes appear with no index key fields defined. The fields actually indexed are not available for querying, and therefore, do not appear in the list.
A roster index must contain the F_WobNum field. If this field is not included in your indexed fields, it is automatically added for you when you close the Index Properties window.
An event log index must contain the F_TimeStamp and F_SeqNumber fields. If these fields are not included in your indexed fields, they are automatically added for you when you close the Index Properties window.
Do not use F_QueueWPClassId as the first or only field for an index on a queue because the system already uses this index internally for cases where two queues share the same physical table.