.. _prefix_index_queries_optimization:

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Prefix Index Queries Optimization
=================================

|Percona Server| has ported Prefix Index Queries Optimization feature from
Facebook patch for |MySQL|.

Prior to this |InnoDB| would always fetch the clustered index for all prefix
columns in an index, even when the value of a particular record was smaller
than the prefix length. This implementation optimizes that case to use the
record from the secondary index and avoid the extra lookup.

Status Variables
================

.. variable:: Innodb_secondary_index_triggered_cluster_reads

   :vartype: Numeric
   :scope: Global

This variable shows the number of times secondary index lookup triggered
cluster lookup.

.. variable:: Innodb_secondary_index_triggered_cluster_reads_avoided

   :vartype: Numeric
   :scope: Global

This variable shows the number of times prefix optimization avoided
triggering cluster lookup.

Version Specific Information
================================================================================

* :rn:`8.0.12-1`: The feature was ported from |Percona Server| 5.7