Joining too many tables is expensive and slow. Stage data from many tables into one for better performance and navigability. Aggregations can cause a bottleneck during query execution. Improve performance by pre-calculating the aggregations and staging them in summary tables. Poor selection criteria.
Indexes increase selection speeds but impede update and insertion performance.
Identify those fields that really need to be indexed and eliminate those that don't. Times of heaviest workload. All business intelligence systems experience peaks and valleys of demand. Manage peak loads and justify infrastructure expenditures by identifying your heaviest resource consumption times by hour, day, week, or month. Users often request more data than is necessary.