From e98942aa7880ec2d3d48cb8c62520a464ab23cec Mon Sep 17 00:00:00 2001
From: Ziyang Hu <hu.ziyang@cantab.net>
Date: Fri, 13 Jan 2023 00:10:57 +0800
Subject: [PATCH] be conservative in index selection

---
 cozo-core/src/runtime/relation.rs | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/cozo-core/src/runtime/relation.rs b/cozo-core/src/runtime/relation.rs
index 8d9e79ba..cd915b24 100644
--- a/cozo-core/src/runtime/relation.rs
+++ b/cozo-core/src/runtime/relation.rs
@@ -160,18 +160,10 @@ impl RelationHandle {
         if self.indices.is_empty() {
             return None;
         }
-        let mut max_prefix_len = 0;
-        let key_len = self.metadata.keys.len();
-        for arg_use in arg_uses {
-            if *arg_use == IndexPositionUse::Join {
-                max_prefix_len += 1;
-                if max_prefix_len == key_len {
-                    break;
-                }
-            } else {
-                break;
-            }
+        if *arg_uses.first().unwrap() == IndexPositionUse::Join {
+            return None;
         }
+        let mut max_prefix_len = 0;
         let required_positions = arg_uses
             .iter()
             .enumerate()