PPT Slide
- Tuple-transfer costs are assumed to dominate the query-execution costs
- Use of “Bound-is-easier” assumption
- Assume availability of full source-statistics
- Selectivity indices, histograms etc.
- Access cost & source latencies tend to equal or dominate the transfer cost
- Need to consider number of source calls
- Need for considering bushy joins (instead of just left-linear join trees)
- Full statistics are rarely available about internet sources
- Sources are decentralized and autonomous
- Difficult to do systematic optimization
Optimization challenges in EMERAC