Cleanup of sql_join_cache code (no logic changes)

- Remove virtual from get_min_join_buffer_size() and
  get_max_join_buffer_size().
- Avoid some calls to get_min_buffer_size()
- Simply cache usage in get_..._join_buffer_size()
- Simplify get_max_join_buffer_size() when using optimize_buff_size
- Reindented some long comments

Reviewer: Sergei Petrunia <sergey@mariadb.com>

sql/sql_join_cache.cc

@@ -694,15 +694,21 @@ void JOIN_CACHE::set_constants()
                (prev_cache ? prev_cache->get_size_of_rec_offset() : 0) + 
                length + fields*sizeof(uint);
   pack_length_with_blob_ptrs= pack_length + blobs*sizeof(uchar *);
-  min_buff_size= 0;
   min_records= 1;
+  min_buff_size= get_min_join_buffer_size();
   buff_size= (size_t)MY_MAX(join->thd->variables.join_buff_size,
-                 get_min_join_buffer_size());
+                            min_buff_size);
   size_of_rec_ofs= offset_size(buff_size);
   size_of_rec_len= blobs ? size_of_rec_ofs : offset_size(len); 
   size_of_fld_ofs= size_of_rec_len;
   base_prefix_length= (with_length ? size_of_rec_len : 0) +
                       (prev_cache ? prev_cache->get_size_of_rec_offset() : 0);
+  /*
+    Call ge_min_join_buffer_size() again as the size may have got smaller
+    if size_of_rec_ofs or some other variable changed since last call.
+  */
+  min_buff_size= 0;
+  min_buff_size= get_min_join_buffer_size();
   /*
     The size of the offsets for referenced fields will be added later.
     The values of 'pack_length' and 'pack_length_with_blob_ptrs' are adjusted
@@ -767,30 +773,29 @@ uint JOIN_CACHE::get_record_max_affix_length()
 
 size_t JOIN_CACHE::get_min_join_buffer_size()
 {
-  if (!min_buff_size)
-  {
-    size_t len= 0;
-    size_t len_last= 0;
+  if (min_buff_size)
+    return min_buff_size;                       // use cached value
+
+  size_t len= 0, len_last= 0, len_addon, min_sz, add_sz= 0;
+
   for (JOIN_TAB *tab= start_tab; tab != join_tab;
        tab= next_linear_tab(join, tab, WITHOUT_BUSH_ROOTS))
   {
     len+= tab->get_max_used_fieldlength();
     len_last+= tab->get_used_fieldlength();
   }
-    size_t len_addon= get_record_max_affix_length() +
-                      get_max_key_addon_space_per_record();
+  len_addon= (get_record_max_affix_length() +
+              get_max_key_addon_space_per_record());
   len+= len_addon;
   len_last+= len_addon;
-    size_t min_sz= len*(min_records-1) + len_last;
+  min_sz= len*(min_records-1) + len_last;
   min_sz+= pack_length_with_blob_ptrs;
-    size_t add_sz= 0;
   for (uint i=0; i < min_records; i++)
     add_sz+= join_tab_scan->aux_buffer_incr(i+1);
   avg_aux_buffer_incr= add_sz/min_records;
   min_sz+= add_sz;
   set_if_bigger(min_sz, 1);
   min_buff_size= min_sz;
-  }
   return min_buff_size;
 }
 
@@ -822,16 +827,21 @@ size_t JOIN_CACHE::get_min_join_buffer_size()
     The maximum possible size of the join buffer of this cache 
 */
 
-size_t JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size)
+size_t JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size,
+                                            size_t min_sz)
 {
-  if (!max_buff_size)
-  {
+  if (max_buff_size)
+    return max_buff_size;                       // use cached value
+
+  size_t limit_sz= (size_t) join->thd->variables.join_buff_size;
+
+  if (!optimize_buff_size)
+    return max_buff_size= limit_sz;
+
   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;
 
@@ -850,20 +860,15 @@ size_t JOIN_CACHE::get_max_join_buffer_size(bool optimize_buff_size)
   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 ((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;
   set_if_smaller(max_sz, limit_sz);
-    }
+
   set_if_bigger(max_sz, min_sz);
   max_buff_size= max_sz;
-  }
   return max_buff_size;
 }
       
@@ -906,11 +911,7 @@ int JOIN_CACHE::alloc_buffer()
   bool optimize_buff_size= 
          optimizer_flag(join->thd, OPTIMIZER_SWITCH_OPTIMIZE_JOIN_BUFFER_SIZE);
   buff= NULL;
-  min_buff_size= 0;
-  max_buff_size= 0;
-  min_records= 1;
-  min_buff_size= get_min_join_buffer_size();
-  buff_size= get_max_join_buffer_size(optimize_buff_size);
+  buff_size= get_max_join_buffer_size(optimize_buff_size, min_buff_size);
 
   for (tab= start_tab; tab!= join_tab; 
        tab= next_linear_tab(join, tab, WITHOUT_BUSH_ROOTS))
@@ -1098,13 +1099,14 @@ int JOIN_CACHE::init(bool for_explain)
     check_emb_key_usage()
 
   DESCRIPTION
-    The function checks some conditions at which the key values can be read
-    directly from the join buffer. This is possible when the key values can be
-    composed by concatenation of the record fields stored in the join buffer.
-    Sometimes when the access key is multi-component the function has to re-order
-    the fields written into the join buffer to make keys embedded. If key 
-    values for the key access are detected as embedded then 'use_emb_key'
-    is set to TRUE.
+    The function checks some conditions at which the key values can be
+    read directly from the join buffer. This is possible when the key
+    values can be composed by concatenation of the record fields
+    stored in the join buffer.  Sometimes when the access key is
+    multi-component the function has to re-order the fields written
+    into the join buffer to make keys embedded. If key values for the
+    key access are detected as embedded then 'use_emb_key' is set to
+    TRUE.
 
   EXAMPLE
     Let table t2 has an index defined on the columns a,b . Let's assume also

sql/sql_join_cache.h

@@ -602,9 +602,10 @@ class JOIN_CACHE :public Sql_alloc
   void set_join_buffer_size(size_t sz) { buff_size= sz; }
 
   /* Get the minimum possible size of the cache join buffer */
-  virtual size_t get_min_join_buffer_size();
+  size_t get_min_join_buffer_size();
   /* Get the maximum possible size of the cache join buffer */ 
-  virtual size_t get_max_join_buffer_size(bool optimize_buff_size);
+  size_t get_max_join_buffer_size(bool optimize_buff_size,
+                                  size_t min_buffer_size_arg);
 
   /* Shrink the size if the cache join buffer in a given ratio */
   bool shrink_join_buffer_in_ratio(ulonglong n, ulonglong d);