opt_statistics.h File Reference

#include <sys/types.h>
#include "my_inttypes.h"

Go to the source code of this file.

Typedefs
typedef float	rec_per_key_t

Functions
rec_per_key_t	guess_rec_per_key (const TABLE *const table, const KEY *const key, uint used_keyparts)
	Guesstimate for "records per key" when index statistics is not available. More...

Typedef Documentation

rec_per_key_t

typedef float rec_per_key_t

Function Documentation

guess_rec_per_key()

rec_per_key_t guess_rec_per_key	(	const TABLE *const	table,
		const KEY *const	key,
		uint	used_keyparts
	)

Guesstimate for "records per key" when index statistics is not available.

Parameters

table	the table
key	the index
used_keyparts	the number of key part that should be included in the estimate

Returns

estimated records per key value

Guesstimate for "records per key" when index statistics is not available.

Assume that the first key part matches 1% of the file and that the whole key matches 10 (duplicates) or 1 (unique) records. For small tables, ensure there are at least ten different key values. Assume also that more key matches proportionally more records. This gives the formula:

records = a - (x-1)/(c-1)*(a-b)

where

b = records matched by whole key a = records matched by first key part (1% of all records?) c = number of key parts in key x = used key parts (1 <= x <= c)