cs/wiki/percona-server:features:innodb_stats#innodb_index_stats">INNODB_INDEX_STATS</a> patch
in Percona Server, and presents with information on InnoDB keys cardinality as per indexed column.
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<p>
The Percona Server INNODB_INDEX_STATS table presents with cardinality values per index, per indexed column. 
That is, it lets us know the average number of rows expected to be found in an index for some key.
</p>

<p>For single column keys, this is simple enough. However, for compound indexes 
(indexes over 