Commit 43439d0c authored by heikki@donna.mysql.fi's avatar heikki@donna.mysql.fi
Browse files

btr0cur.c, ha_innobase.cc: 

  Fine-tune optimization parameters; in small tables the estimates are accurate; in big tables let us not be too optimistic about index selectivity
parent b908f410

innobase/btr/btr0cur.c

+19 −1
Original line number Diff line number Diff line
@@ -2552,6 +2552,7 @@ btr_estimate_number_of_different_key_vals( 
	ulint		total_external_size = 0;

	ulint		i;

	ulint		j;

	ulint		add_on;

	mtr_t		mtr;



	n_cols = dict_index_get_n_unique(index);
@@ -2624,6 +2625,23 @@ btr_estimate_number_of_different_key_vals( 
				 + not_empty_flag)

		                	/ (BTR_KEY_VAL_ESTIMATE_N_PAGES

		                	   + total_external_size);

	

		/* If the tree is small, smaller than <

		10 * BTR_KEY_VAL_ESTIMATE_N_PAGES + total_external_size, then

		the above estimate is ok. For bigger trees it is common that we

		do not see any borders between key values in the few pages

		we pick. But still there may be BTR_KEY_VAL_ESTIMATE_N_PAGES

		different key values, or even more. Let us try to approximate

		that: */



		add_on = index->stat_n_leaf_pages /

		   (10 * (BTR_KEY_VAL_ESTIMATE_N_PAGES + total_external_size));



		if (add_on > BTR_KEY_VAL_ESTIMATE_N_PAGES) {

			add_on = BTR_KEY_VAL_ESTIMATE_N_PAGES;

		}

		

		index->stat_n_diff_key_vals[j] += add_on;

	}

		

	mem_free(n_diff);

sql/ha_innobase.cc

+0 −16
Original line number Diff line number Diff line
@@ -3130,22 +3130,6 @@ ha_innobase::info( 
					rec_per_key = 1;

				}

			

				/* Since the MySQL optimizer is often too

				pessimistic in the assumption that a table

				does not fit in the buffer pool, we

				increase the attractiveness of indexes

				by assuming the selectivity of any prefix

				of an index is 1 / 100 or better.

				(Actually, we should look at the table

				size, and if the table is smaller than

				the buffer pool, we should uniformly

				increase the attractiveness of indexes,

				regardless of the estimated selectivity.) */



			        if (rec_per_key > records / 100) {

				        rec_per_key = records / 100;

				}



				table->key_info[i].rec_per_key[j]

								= rec_per_key;

			}