iTop/quick_impact_analysis.md

An attempt to accelerate the process of impact analysis by relying on recursive queries

TODO to prove the concept

• Integrate the recursive query into the process of building the impact graph
• Improve to cope with backtracking on redundancy nodes
• Optimize context management
  • Reduce the number of queries
  • See how to cache the queries (IN clause prevents caching)
• Restore redundancy computation

TODO to finalize the feature

• Unit tests for the whole stuff
• Deshardcode the query against the source nodes
• Deshardcode the query against the datamodel
  • Get the algorithm from make_quick_impact_query.php
  • Find a clean way to hack queries
  • Eliminate the limitation on unions
  • Cache (parts of) the query
• Review the KPIs
• Decide if the legacy algorithm should be kept (opt-in/out)
• Do not load persistent objects in the impact graph as they are not needed (tooltip loaded by ajax calls)

Metrics

To to build the impact graph with 520 CIs

Operation	Legacy	Optimized	Fix overhead in optimized version	Time per CI in optimized version
Build logical graph	2.5 s	0.4 s	0 s	0,7 ms
Integrate context	2 s	0.8 s	0,78 s	0,1 ms
Graphviz	0.4 s	0.4 s	0,4 s	0 ms
Total	4.9 s	1.6 s	1.18 s	0,8 ms

Comments:

• Graphviz execution time is the time for Windows to spawn the process, so it is not really relevant
• In the optimized version, building the logical graph still require to instantiate the objects which is done with one query per class, but it does not seem to be a must
• For small graphs, the overhead on context queries can be questioned