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Measure Recall since v0.5.0 ​

In the context of vector search, recall is the ratio of true nearest neighbors to approximate nearest neighbors returned by the index. For example, if the index retrieves approximate nearest neighbors and of them are true nearest neighbors, then the recall is .

Recall measures the ratio of relevant results to all results retrieved from a search. When using an index, you likely want to know the recall and QPS corresponding to different parameters. The function vchordrq_evaluate_query_recall is designed for evaluating recall. It receives a query that returns row identifiers and returns the corresponding recall.

sql
SET vchordrq.probes = '100';
SET vchordrq.epsilon = 1.0;
SELECT vchordrq_evaluate_query_recall(query => $$
  SELECT ctid FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 10);
$$);

By default, the function evaluates the recall by generating estimated ground truth with another index scan. If you would like to evaluate the recall by generating ground truth with a table scan, set the function parameter exact_search to true.

sql
SET vchordrq.probes = '100';
SET vchordrq.epsilon = 1.0;
SELECT vchordrq_evaluate_query_recall(query => $$
  SELECT ctid FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 10
$$, exact_search => true);

Reference ​

This feature is not supported by vchordg.

Functions vchordrq ​

vchordrq_evaluate_query_recall since v0.5.0 ​

  • Description: Evaluates the recall of a given vchordrq query.
  • Result: real
  • Arguments:
    • query: text, the query whose recall is evaluated
    • exact_search: boolean, use ground truth instead of estimated ground truth
    • accu_probes: text, vchordrq.probes for estimated ground truth
    • accu_epsilon: real, vchordrq.epsilon for estimated ground truth
  • Example:
    • SELECT vchordrq_evaluate_query_recall(query => $$ SELECT ctid FROM t ORDER BY val <-> '[0.5, 0.25, 1.0]' LIMIT 10 $$);
    • SELECT vchordrq_evaluate_query_recall(query => $$ SELECT ctid FROM t ORDER BY val <-> '[0.5, 0.25, 1.0]' LIMIT 10 $$, exact_search => true);
    • SELECT vchordrq_evaluate_query_recall(query => $$ SELECT ctid FROM t ORDER BY val <-> '[0.5, 0.25, 1.0]' LIMIT 10 $$, accu_probes => '9999', accu_epsilon => 4.0);