Why does increasing the full text merge limit cause performance problems in IBM Rational Team Concert?
The Work Item Queries section of the Advanced Configuration in the Jazz Team server contains a configuration property called Full Text Merge Limit. When the property is hovered upon, the description indicates some level of performance may be compromised by setting this feature high.
The explanation indicates:
The number of full text results that will be merged with a structured query part. Technically, this is the size of an IN clause. Setting this parameter to a high value may have a severe impact on performance.
The full text merge limit has an impact on the query performance.
The default configuration of 100 means that the full text index is queried for full text results up to 100 work items. After the first 100 work items, the results are merged into a real work item query using the IN SQL statement.
If all open work items are searched for with some text, the query would first retrieve 100 results from the full text index that match the text and then add 100 work item IDs into a SQL query (similar to WHERE status = open AND...).
Adjusting the full text limit to a higher value will produce potentially better results at the cost of query execution performance. That is, the higher the merge limit is, the longer the query will execute, and therefore a larger impact on database performance.
Jazz and Rational Team Concert have an active community that can provide you with additional resources. Browse and contribute to the User forums, contribute to the Team Blog and review the Team wiki.
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