From ac79f79637ae3f1050be6498d82ba80a63c071ff Mon Sep 17 00:00:00 2001
From: Andrew Kane <andrew@ankane.org>
Date: Sat, 20 Jan 2024 17:07:36 -0800
Subject: [PATCH] Allow override

---
 src/hnsw.c                    | 21 ++++++++++++++++-----
 test/t/015_hnsw_duplicates.pl |  5 ++---
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/hnsw.c b/src/hnsw.c
index 255d06f..b498bad 100644
--- a/src/hnsw.c
+++ b/src/hnsw.c
@@ -83,11 +83,8 @@ hnswcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 	List	   *qinfos;
 #endif
 
-	/*
-	 * Never use index without order or limit, or if limit + offset >
-	 * ef_search
-	 */
-	if (path->indexorderbys == NULL || root->limit_tuples < 0 || root->limit_tuples > hnsw_ef_search)
+	/* Never use index without order or limit */
+	if (path->indexorderbys == NULL || root->limit_tuples < 0)
 	{
 		*indexStartupCost = DBL_MAX;
 		*indexTotalCost = DBL_MAX;
@@ -97,6 +94,20 @@ hnswcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
 		return;
 	}
 
+	/*
+	 * Do not use index if limit + offset > ef_search unless enable_seqscan =
+	 * off
+	 */
+	if (root->limit_tuples > hnsw_ef_search)
+	{
+		*indexStartupCost = 1.0e10 - 1;
+		*indexTotalCost = 1.0e10 - 1;
+		*indexSelectivity = 0;
+		*indexCorrelation = 0;
+		*indexPages = 0;
+		return;
+	}
+
 	MemSet(&costs, 0, sizeof(costs));
 
 	index = index_open(path->indexinfo->indexoid, NoLock);
diff --git a/test/t/015_hnsw_duplicates.pl b/test/t/015_hnsw_duplicates.pl
index 4cc7f03..874ec43 100644
--- a/test/t/015_hnsw_duplicates.pl
+++ b/test/t/015_hnsw_duplicates.pl
@@ -23,11 +23,10 @@ sub insert_vectors
 
 sub test_duplicates
 {
-	# TODO Improve
 	my $res = $node->safe_psql("postgres", qq(
 		SET enable_seqscan = off;
-		SET hnsw.ef_search = 10;
-		SELECT COUNT(*) FROM (SELECT * FROM tst ORDER BY v <-> '[1,1,1]' LIMIT 10) t;
+		SET hnsw.ef_search = 1;
+		SELECT COUNT(*) FROM (SELECT * FROM tst ORDER BY v <-> '[1,1,1]' LIMIT 20) t;
 	));
 	is($res, 10);
 }