Execution plans

[mikegoatly]

Given the work that went into v6 to optimise the query execution paths, having a way to visualize the order that each query part was executed in would help:

1. Explain how queries are executed, including the weightings that were calculated for each part
2. Spot any obvious improvements that could be made to the execution order.

Conceptually similar to SQL Server's actual execution plan generation, this would be opt-in when queries are executed against an index:

var results = this.index.Search("\"two three four\"", QueryExecutionOptions.IncludeExecutionPlan);

var executionPlan = results.GetExecutionPlan();

A execution plan would be a hierarchical tree of the query parts, including timing details and scoring breakdowns. For example:

You can see that:

• 1 "CHANGE" was executed first because it had the lowest weighting of the two intersecting queries, matching 3 documents
• 2 The "THE" query part was executed second, and had its results pre-filtered to the 3 documents already matched for the intersection
• 3 The results from the AND operators were intersected, resulting in 3 matches
• 4 "WORLD" was executed fourth, returning 14 documents
• 5 lastly, unioning (ORing) the two parts of the query together resulted in 17 document matches