Fixed calculation of JOIN_CACHE::max_records

The old code did set max_records to either number_of_rows
(partial_join_cardinality) or memory size (join_buffer_space_limit)
which did not make sense.

Fixed by setting max_records to number of rows that fits into
join_buffer_size.

Other things:
- Initialize buffer cache values in JOIN_CACHE constructors (safety)

Reviewer: Sergei Petrunia <sergey@mariadb.com>

mysql-test/main/join_cache.result

@@ -3781,9 +3781,9 @@ id1	num3	text1	id4	id3	dummy
 228808822	6	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	18	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	1	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
-228808822	3	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	17	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	50	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
+228808822	3	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	4	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	826928662	935693782	0
 228808822	89	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	2381969632	2482416112	0
 228808822	19	CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC	2381969632	2482416112	0

sql/sql_join_cache.cc

@@ -829,6 +829,12 @@ size_t JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size)
     size_t max_sz;
     size_t min_sz= get_min_join_buffer_size(); 
     size_t len= 0;
+    double max_records, partial_join_cardinality=
+      (join_tab-1)->get_partial_join_cardinality();
+    size_t limit_sz= (size_t) join->thd->variables.join_buff_size;
+    /* Expected join buffer space used for one record */
+    size_t space_per_record;
+
     for (JOIN_TAB *tab= start_tab; tab != join_tab;
          tab= next_linear_tab(join, tab, WITHOUT_BUSH_ROOTS))
     {
@@ -839,13 +845,17 @@ size_t JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size)
     len+= get_max_key_addon_space_per_record() + avg_aux_buffer_incr;
     space_per_record= len;
     
-    size_t limit_sz= (size_t)join->thd->variables.join_buff_size;
+    /* Note that space_per_record can be 0 if no table fields where used */
+    max_records= (double) (limit_sz / MY_MAX(space_per_record, 1));
+    set_if_smaller(max_records, partial_join_cardinality);
+    set_if_bigger(max_records, 10.0);
+
     if (!optimize_buff_size)
       max_sz= limit_sz;
     else
     {    
-      if (limit_sz / max_records > space_per_record)
-        max_sz= space_per_record * max_records;
+      if ((size_t) (limit_sz / max_records) > space_per_record)
+        max_sz= space_per_record * (size_t) max_records;
       else
         max_sz= limit_sz;
       max_sz+= pack_length_with_blob_ptrs;
@@ -895,14 +905,10 @@ int JOIN_CACHE::alloc_buffer()
     join->thd->variables.join_buff_space_limit;
   bool optimize_buff_size= 
          optimizer_flag(join->thd, OPTIMIZER_SWITCH_OPTIMIZE_JOIN_BUFFER_SIZE);
-  double partial_join_cardinality=  (join_tab-1)->get_partial_join_cardinality();
   buff= NULL;
   min_buff_size= 0;
   max_buff_size= 0;
   min_records= 1;
-  max_records= (size_t) (partial_join_cardinality <= join_buff_space_limit ?
-                 (ulonglong) partial_join_cardinality : join_buff_space_limit);
-  set_if_bigger(max_records, 10);
   min_buff_size= get_min_join_buffer_size();
   buff_size= get_max_join_buffer_size(optimize_buff_size);
 

sql/sql_join_cache.h

@@ -248,9 +248,6 @@ class JOIN_CACHE :public Sql_alloc
   /* The expected size of the space per record in the auxiliary buffer */
   size_t avg_aux_buffer_incr;
 
-  /* Expected join buffer space used for one record */
-  size_t space_per_record; 
-
   /* Pointer to the beginning of the join buffer */
   uchar *buff;         
   /* 
@@ -272,11 +269,6 @@ class JOIN_CACHE :public Sql_alloc
     the minimal size equal to min_buff_size
   */
   size_t min_records;
-  /*
-    The maximum expected number of records to be put in the join buffer
-    at one refill 
-  */
-  size_t max_records;
 
   /* 
     Pointer to the current position in the join buffer.
@@ -542,6 +534,7 @@ class JOIN_CACHE :public Sql_alloc
     join_tab= tab;
     prev_cache= next_cache= 0;
     buff= 0;
+    min_buff_size= max_buff_size= 0;            // Caches
   }
 
   /* 
@@ -557,6 +550,7 @@ class JOIN_CACHE :public Sql_alloc
     next_cache= 0;
     prev_cache= prev;
     buff= 0;
+    min_buff_size= max_buff_size= 0;            // Caches
     if (prev)
       prev->next_cache= this;
   }