2 Jan
2016
2 Jan
'16
9:22 a.m.
Hi! I was playing around with indexes after we faced problems with mariadb choosing the wrong index because of high average value group size. So I created a table with 4 text columns and indexed the 4th column with a prefix length of 1. Following are the stats in brief -- The index has 35 unique values There are around 1040000 rows in total. this will give an average value group size of 29714 Cardinality is calculated as <no. of records in the index>/<average size of value groups>, thus it's value must be 35 BUT from show indexes, it's value is shown as 72 (innodb_stats_persistent_sample_pages = 9999999).