Commit 6ecaac01 authored by sasha@mysql.sashanet.com's avatar sasha@mysql.sashanet.com
Browse files

count(distinct) cleanup

parent 73e6a690

mysql-test/t/count_distinct2.test

+1 −1
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ select count(distinct n2), n1 from t1 group by n1; 
drop table t1;



# test the converstion from tree to MyISAM

create table t1 (n int);

create table t1 (n int default NULL);

let $1=5000;

while ($1)

{

sql/item_sum.cc

+8 −2
Original line number Diff line number Diff line
@@ -839,7 +839,8 @@ int dump_leaf(byte* key, uint32 count __attribute__((unused)), 
{

  char* buf = item->table->record[0];

  int error;

  memset(buf, 0xff, item->rec_offset); // make up for cheating in the tree

  // the first item->rec_offset bytes are taken care of with

  // restore_record(table,2) in setup()

  memcpy(buf + item->rec_offset, key, item->tree.size_of_element);

  if ((error = item->table->file->write_row(buf)))

  {
@@ -888,6 +889,7 @@ bool Item_sum_count_distinct::setup(THD *thd) 
  table->file->extra(HA_EXTRA_NO_ROWS);		// Don't update rows

  table->no_rows=1;



  

  if(table->db_type == DB_TYPE_HEAP) // no blobs, otherwise it would be

    // MyISAM

    {
@@ -895,6 +897,10 @@ bool Item_sum_count_distinct::setup(THD *thd) 
      void* cmp_arg;

      int key_len;



      // to make things easier for dump_leaf if we ever have to dump to

      // MyISAM

      restore_record(table,2);

      

      if(table->fields == 1) // if we have only one field, which is

	// the most common use of count(distinct), it is much faster

	// to use a simpler key compare method that can take advantage
@@ -941,7 +947,7 @@ bool Item_sum_count_distinct::setup(THD *thd) 
      // but this has to be handled - otherwise someone can crash

      // the server with a DoS attack

      max_elements_in_tree = (key_len) ? max_heap_table_size/key_len :

	max_heap_table_size;

	1;

    }

  

  return 0;

sql/item_sum.h

+4 −3
Original line number Diff line number Diff line
@@ -148,19 +148,20 @@ class Item_sum_count_distinct :public Item_sum_int 
  bool fix_fields(THD *thd,TABLE_LIST *tables);

  TMP_TABLE_PARAM *tmp_table_param;

  TREE tree;

  uint max_elements_in_tree;

  

  // calculated based on max_heap_table_size. If reached,

  // walk the tree and dump it into MyISAM table

  uint max_elements_in_tree;

  

  bool use_tree;

  // If there are no blobs, we can use a tree, which

  // is faster than heap table. In that case, we still use the table

  // to help get things set up, but we insert nothing in it

  bool use_tree;

  

  int rec_offset;

  // the first few bytes of record ( at least one)

  // are just markers for deleted and NULLs. We want to skip them since

  // they will just bloat the tree without providing any valuable info

  int rec_offset;



  int tree_to_myisam();