1 files changed, 23 insertions, 8 deletions

diff --git a/storage/innobase/include/btr0cur.h b/storage/innobase/include/btr0cur.h
index 12aaa73ae30..1f1ac2a09e7 100644
--- a/storage/innobase/include/btr0cur.h
+++ b/storage/innobase/include/btr0cur.h
@@ -614,8 +614,24 @@ btr_estimate_n_rows_in_range(
 	const dtuple_t*	tuple2,
 	page_cur_mode_t	mode2);
 
-/*******************************************************************//**
-Estimates the number of different key values in a given index, for
+
+/** Statistics for one field of an index. */
+struct index_field_stats_t
+{
+  ib_uint64_t n_diff_key_vals;
+  ib_uint64_t n_sample_sizes;
+  ib_uint64_t n_non_null_key_vals;
+
+  index_field_stats_t(ib_uint64_t n_diff_key_vals= 0,
+                      ib_uint64_t n_sample_sizes= 0,
+                      ib_uint64_t n_non_null_key_vals= 0)
+      : n_diff_key_vals(n_diff_key_vals), n_sample_sizes(n_sample_sizes),
+        n_non_null_key_vals(n_non_null_key_vals)
+  {
+  }
+};
+
+/** Estimates the number of different key values in a given index, for
 each n-column prefix of the index where 1 <= n <= dict_index_get_n_unique(index).
 The estimates are stored in the array index->stat_n_diff_key_vals[] (indexed
 0..n_uniq-1) and the number of pages that were sampled is saved in
@@ -623,12 +639,11 @@ index->stat_n_sample_sizes[].
 If innodb_stats_method is nulls_ignored, we also record the number of
 non-null values for each prefix and stored the estimates in
 array index->stat_n_non_null_key_vals.
-@return true if the index is available and we get the estimated numbers,
-false if the index is unavailable. */
-bool
-btr_estimate_number_of_different_key_vals(
-/*======================================*/
-	dict_index_t*	index);	/*!< in: index */
+@param[in]	index	index
+@return stat vector if the index is available and we get the estimated numbers,
+empty vector if the index is unavailable. */
+std::vector<index_field_stats_t>
+btr_estimate_number_of_different_key_vals(dict_index_t* index);
 
 /** Gets the externally stored size of a record, in units of a database page.
 @param[in]	rec	record