output.txt

# CREATE INDEX output omitted
psql:repro.sql:8: INFO:  vector_l2_squared_distance
psql:repro.sql:8: INFO:  vector_l2_squared_distance
psql:repro.sql:8: INFO:  vector_l2_squared_distance
psql:repro.sql:8: INFO:  vector_l2_squared_distance
psql:repro.sql:8: INFO:  vector_l2_squared_distance
psql:repro.sql:8: INFO:  l2_distance
psql:repro.sql:8: INFO:  l2_distance
 id 
----
  1
  2
(2 rows)

repro.patch

diff --git a/src/vector.c b/src/vector.c
index 2f1e886..bf6c01a 100644
--- a/src/vector.c
+++ b/src/vector.c
@@ -563,6 +563,8 @@ l2_distance(PG_FUNCTION_ARGS)
        float           distance = 0.0;
        float           diff;
 
+       elog(INFO, "l2_distance");
+
        CheckDims(a, b);
 
        /* Auto-vectorized */
@@ -590,6 +592,8 @@ vector_l2_squared_distance(PG_FUNCTION_ARGS)
        float           distance = 0.0;
        float           diff;
 
+       elog(INFO, "vector_l2_squared_distance");
+
        CheckDims(a, b);
 
        /* Auto-vectorized */

repro.sql

SET enable_seqscan = off;

DROP TABLE IF EXISTS items;
CREATE TABLE items (id bigserial primary key, embedding vector(3));
INSERT INTO items (embedding) VALUES ('[0,0,0]'), ('[1,1,1]'), ('[2,2,2]'), ('[3,3,3]');
CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 1);

SELECT id FROM items ORDER BY embedding <-> '[0,0,0]' LIMIT 2;