How to read the EXPLAIN execution plan and output of PROFILE?

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Last updated 22, Mar 2024

Question

How to read the EXPLAIN execution plan and output of PROFILE?

Answer

Let's consider the following explain plan of a hybrid vector similarity search query that performs also a full-text search and a tag search.

FT.EXPLAIN doc_idx (@content:(carbonara) @genre:{technical})=>[KNN 2 @embedding $vec AS score] 
RETURN 1 score 
DIALECT 2 
LIMIT 0 10 
params 2 vec \x0e\xaf\xae<\xac\x92\x96< [...]

This is the output produced by the FT.EXPLAIN command:

VECTOR {
  INTERSECT {
    @content:carbonara
    TAG:@genre {
      technical
    }
  }
} => {K=2 nearest vectors to `$vec` in vector index associated with field @embedding, yields distance as `score`}

The internal section (the INTERSECT, in this example) is a pre-filter and returns the KNN results from the induced sub-space. This holds for both FLAT and HNSW indexing methods.

The FT.PROFILE command of this same query, instead, would return the following output.

(Result{0 total, docs: []}, {'Total profile time': 1.0, 'Parsing time': 1.0, 'Pipeline creation time': 0.0, 'Iterators profile': {'Type': 'VECTOR', 'Time': 0.0, 'Counter': 0.0, 'Child iterators': [{'Type': 'INTERSECT', 'Time': 0.0, 'Counter': 0.0, 'Child iterators': [{'Type': 'TEXT', 'Term': 'carbonara', 'Time': 0.0, 'Counter': 4.0, 'Size': 4.0}, {'Type': 'TAG', 'Term': 'technical', 'Time': 0.0, 'Counter': 3.0, 'Size': 4.0}]}]}, 'Result processors profile': {'Type': 'Index', 'Time': 0.0, 'Counter': 0.0}})

References

Learn more about the FT.EXPLAIN and FT.INFO commands.