From f4503f39ee09a11d3b5f35eb0290d59e5d0e902b Mon Sep 17 00:00:00 2001
From: Igor Babaev <igor@askmonty.org>
Date: Tue, 21 Sep 2010 16:41:53 -0700
Subject: [PATCH] Fixed bug #52394 / LP bug #623209. When an incremental join
 cache is used to join a table whose fields are not referenced anywhere in the
 query the association pointer to the last record in the such cache can be the
 same as the pointer to the end of the buffer. The function
 JOIN_CACHE_BKA::get_next_key must take into consideration this when iterating
 over the keys of the records from the join buffer. The assertion in
 JOIN_TAB_SCAN_MRR::next also must take this into consideration. Borrowed a
 slightly changed test case from a patch attached to the bug #52394.

---
 mysql-test/r/join_cache.result | 28 ++++++++++++++++++++++++++++
 mysql-test/t/join_cache.test   | 28 ++++++++++++++++++++++++++++
 sql/sql_join_cache.cc          | 12 ++++++++----
 3 files changed, 64 insertions(+), 4 deletions(-)
 mode change 100755 => 100644 mysql-test/r/join_cache.result

diff --git a/mysql-test/r/join_cache.result b/mysql-test/r/join_cache.result
old mode 100755
new mode 100644
index 22ec45e6d25..f19243961b8
--- a/mysql-test/r/join_cache.result
+++ b/mysql-test/r/join_cache.result
@@ -5174,3 +5174,31 @@ a	b
 set join_cache_level=default;
 drop table t1,t2,t3;
 set @@optimizer_switch=@save_optimizer_switch;
+#
+# Bug #52394:  using join buffer for 3 table join with ref access 
+# LP #623209: and no references to the columns of the middle table
+#
+set join_cache_level=6;
+CREATE TABLE t1 (a int(11), b varchar(1));
+INSERT INTO t1 VALUES (6,'r'),(27,'o');
+CREATE TABLE t2(a int);
+INSERT INTO t2 VALUES(1),(2),(3),(4),(5);
+CREATE TABLE t3 (a int(11) primary key, b varchar(1));
+INSERT INTO t3 VALUES
+(14,'d'),(15,'z'),(16,'e'),(17,'h'),(18,'b'),(19,'s'),(20,'e'),
+(21,'j'),(22,'e'),(23,'f'),(24,'v'),(25,'x'),(26,'m'),(27,'o');
+EXPLAIN
+SELECT t3.a FROM t1,t2,t3 WHERE t1.a = t3.a AND t1.b = t3.b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	5	Using join buffer
+1	SIMPLE	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.a	1	Using where; Using join buffer
+SELECT t3.a FROM t1,t2,t3 WHERE t1.a = t3.a AND t1.b = t3.b;
+a
+27
+27
+27
+27
+27
+DROP TABLE t1,t2,t3;
+set join_cache_level=default;
diff --git a/mysql-test/t/join_cache.test b/mysql-test/t/join_cache.test
index 68693fe70eb..7bc22fd4f23 100755
--- a/mysql-test/t/join_cache.test
+++ b/mysql-test/t/join_cache.test
@@ -1956,3 +1956,31 @@ set join_cache_level=default;
 drop table t1,t2,t3;
 
 set @@optimizer_switch=@save_optimizer_switch;
+
+--echo #
+--echo # Bug #52394:  using join buffer for 3 table join with ref access 
+--echo # LP #623209: and no references to the columns of the middle table
+--echo #
+
+
+set join_cache_level=6;
+
+CREATE TABLE t1 (a int(11), b varchar(1));
+INSERT INTO t1 VALUES (6,'r'),(27,'o');
+
+CREATE TABLE t2(a int);
+INSERT INTO t2 VALUES(1),(2),(3),(4),(5);
+
+CREATE TABLE t3 (a int(11) primary key, b varchar(1));
+INSERT INTO t3 VALUES
+(14,'d'),(15,'z'),(16,'e'),(17,'h'),(18,'b'),(19,'s'),(20,'e'),
+(21,'j'),(22,'e'),(23,'f'),(24,'v'),(25,'x'),(26,'m'),(27,'o');
+
+EXPLAIN
+SELECT t3.a FROM t1,t2,t3 WHERE t1.a = t3.a AND t1.b = t3.b;
+SELECT t3.a FROM t1,t2,t3 WHERE t1.a = t3.a AND t1.b = t3.b;
+
+DROP TABLE t1,t2,t3;
+
+set join_cache_level=default;
+
diff --git a/sql/sql_join_cache.cc b/sql/sql_join_cache.cc
index f48db588fa6..947e3b3c9f1 100755
--- a/sql/sql_join_cache.cc
+++ b/sql/sql_join_cache.cc
@@ -3391,8 +3391,12 @@ int JOIN_TAB_SCAN_MRR::next()
   uint rc= join_tab->table->file->multi_range_read_next(ptr) ? -1 : 0;
   if (!rc)
   {
+    /* 
+      If a record in in an incremental cache contains no fields then the
+      association for the last record in cache will be equal to cache->end_pos
+    */ 
     DBUG_ASSERT(cache->buff <= (uchar *) (*ptr) &&
-                (uchar *) (*ptr) < cache->end_pos);
+                (uchar *) (*ptr) <= cache->end_pos);
     update_virtual_fields(join_tab->table);
   }
   return rc;
@@ -3728,12 +3732,12 @@ uint JOIN_CACHE_BKA::get_next_key(uchar ** key)
   uchar *init_pos;
   JOIN_CACHE *cache;
   
-  if (pos > last_rec_pos || !records)
-    return 0;
-
   /* Any record in a BKA cache is prepended with its length */
   DBUG_ASSERT(with_length);
    
+  if ((pos+size_of_rec_len) > last_rec_pos || !records)
+    return 0;
+
   /* Read the length of the record */
   rec_len= get_rec_length(pos);
   pos+= size_of_rec_len;