Provided by: percona-toolkit_3.0.13-1_all bug


       pt-index-usage - Read queries from a log and analyze how they use indexes.


       Usage: pt-index-usage [OPTIONS] [FILES]

       pt-index-usage reads queries from logs and analyzes how they use indexes.

       Analyze queries in slow.log and print reports:

         pt-index-usage /path/to/slow.log --host localhost

       Disable reports and save results to percona database for later analysis:

         pt-index-usage slow.log --no-report --save-results-database percona


       Percona Toolkit is mature, proven in the real world, and well tested, but all database
       tools can pose a risk to the system and the database server.  Before using this tool,

       ·   Read the tool's documentation

       ·   Review the tool's known "BUGS"

       ·   Test the tool on a non-production server

       ·   Backup your production server and verify the backups


       This tool connects to a MySQL database server, reads through a query log, and uses EXPLAIN
       to ask MySQL how it will use each query.  When it is finished, it prints out a report on
       indexes that the queries didn't use.

       The query log needs to be in MySQL's slow query log format.  If you need to input a
       different format, you can use pt-query-digest to translate the formats.  If you don't
       specify a filename, the tool reads from STDIN.

       The tool runs two stages.  In the first stage, the tool takes inventory of all the tables
       and indexes in your database, so it can compare the existing indexes to those that were
       actually used by the queries in the log.  In the second stage, it runs EXPLAIN on each
       query in the query log.  It uses separate database connections to inventory the tables and
       run EXPLAIN, so it opens two connections to the database.

       If a query is not a SELECT, it tries to transform it to a roughly equivalent SELECT query
       so it can be EXPLAINed.  This is not a perfect process, but it is good enough to be

       The tool skips the EXPLAIN step for queries that are exact duplicates of those seen
       before.  It assumes that the same query will generate the same EXPLAIN plan as it did
       previously (usually a safe assumption, and generally good for performance), and simply
       increments the count of times that the indexes were used.  However, queries that have the
       same fingerprint but different checksums will be re-EXPLAINed.  Queries that have
       different literal constants can have different execution plans, and this is important to

       After EXPLAIN-ing the query, it is necessary to try to map aliases in the query back to
       the original table names.  For example, consider the EXPLAIN plan for the following query:

         SELECT * FROM tbl1 AS foo;

       The EXPLAIN output will show access to table "foo", and that must be translated back to
       "tbl1".  This process involves complex parsing.  It is generally very accurate, but there
       is some chance that it might not work right.  If you find cases where it fails, submit a
       bug report and a reproducible test case.

       Queries that cannot be EXPLAINed will cause all subsequent queries with the same
       fingerprint to be blacklisted.  This is to reduce the work they cause, and prevent them
       from continuing to print error messages.  However, at least in this stage of the tool's
       development, it is my opinion that it's not a good idea to preemptively silence these, or
       prevent them from being EXPLAINed at all.  I am looking for lots of feedback on how to
       improve things like the query parsing.  So please submit your test cases based on the
       errors the tool prints!


       After it reads all the events in the log, the tool prints out DROP statements for every
       index that was not used.  It skips indexes for tables that were never accessed by any
       queries in the log, to avoid false-positive results.

       If you don't specify "--quiet", the tool also outputs warnings about statements that
       cannot be EXPLAINed and similar.  These go to standard error.

       Progress reports are enabled by default (see "--progress").  These also go to standard


       This tool accepts additional command-line arguments.  Refer to the "SYNOPSIS" and usage
       information for details.

           Prompt for a password when connecting to MySQL.

           short form: -A; type: string

           Default character set.  If the value is utf8, sets Perl's binmode on STDOUT to utf8,
           passes the mysql_enable_utf8 option to DBD::mysql, and runs SET NAMES UTF8 after
           connecting to MySQL.  Any other value sets binmode on STDOUT without the utf8 layer,
           and runs SET NAMES after connecting to MySQL.

           type: Array

           Read this comma-separated list of config files; if specified, this must be the first
           option on the command line.

           Create the "--save-results-database" if it does not exist.

           If the "--save-results-database" already exists and this option is specified, the
           database is used and the necessary tables are created if they do not already exist.

           Create views for "--save-results-database" example queries.

           Several example queries are given for querying the tables in the
           "--save-results-database".  These example queries are, by default, created as views.
           Specifying "--no-create-views" prevents these views from being created.

           short form: -D; type: string

           The database to use for the connection.

           short form: -d; type: hash

           Only get tables and indexes from this comma-separated list of databases.

           type: string

           Only get tables and indexes from database whose names match this Perl regex.

           short form: -F; type: string

           Only read mysql options from the given file.  You must give an absolute pathname.

           type: Hash; default: non-unique

           Suggest dropping only these types of unused indexes.

           By default pt-index-usage will only suggest to drop unused secondary indexes, not
           primary or unique indexes.  You can specify which types of unused indexes the tool
           suggests to drop: primary, unique, non-unique, all.

           A separate "ALTER TABLE" statement for each type is printed.  So if you specify
           "--drop all" and there is a primary key and a non-unique index, the "ALTER TABLE ...
           DROP" for each will be printed on separate lines.

           Drop and re-create all pre-existing tables in the "--save-results-database".  This
           allows information from previous runs to be removed before the current run.

           Show help and exit.

           short form: -h; type: string

           Connect to host.

           type: Hash

           Ignore this comma-separated list of databases.

           type: string

           Ignore databases whose names match this Perl regex.

           type: Hash

           Ignore this comma-separated list of table names.

           Table names may be qualified with the database name.

           type: string

           Ignore tables whose names match the Perl regex.

           short form: -p; type: string

           Password to use when connecting.  If password contains commas they must be escaped
           with a backslash: "exam\,ple"

           short form: -P; type: int

           Port number to use for connection.

           type: array; default: time,30

           Print progress reports to STDERR.  The value is a comma-separated list with two parts.
           The first part can be percentage, time, or iterations; the second part specifies how
           often an update should be printed, in percentage, seconds, or number of iterations.

           short form: -q

           Do not print any warnings.  Also disables "--progress".

           default: yes

           Print the reports for "--report-format".

           You may want to disable the reports by specifying "--no-report" if, for example, you
           also specify "--save-results-database" and you only want to query the results tables

           type: Array; default: drop_unused_indexes

           Right now there is only one report: drop_unused_indexes.  This report prints SQL
           statements for dropping any unused indexes.  See also "--drop".

           See also "--[no]report".

           type: DSN

           Save results to tables in this database.  Information about indexes, queries, tables
           and their usage is stored in several tables in the specified database.  The tables are
           auto-created if they do not exist.  If the database doesn't exist, it can be auto-
           created with "--create-save-results-database".  In this case the connection is
           initially created with no default database, then after the database is created, it is

           pt-index-usage executes INSERT statements to save the results.  Therefore, you should
           be careful if you use this feature on a production server.  It might increase load, or
           cause trouble if you don't want the server to be written to, or so on.

           This is a new feature.  It may change in future releases.

           After a run, you can query the usage tables to answer various questions about index
           usage.  The tables have the following CREATE TABLE definitions:


             CREATE TABLE IF NOT EXISTS indexes (
               db           VARCHAR(64) NOT NULL,
               tbl          VARCHAR(64) NOT NULL,
               idx          VARCHAR(64) NOT NULL,
               cnt          BIGINT UNSIGNED NOT NULL DEFAULT 0,
               PRIMARY KEY  (db, tbl, idx)


             CREATE TABLE IF NOT EXISTS queries (
               query_id     BIGINT UNSIGNED NOT NULL,
               fingerprint  TEXT NOT NULL,
               sample       TEXT NOT NULL,
               PRIMARY KEY  (query_id)


             CREATE TABLE IF NOT EXISTS tables (
               db           VARCHAR(64) NOT NULL,
               tbl          VARCHAR(64) NOT NULL,
               cnt          BIGINT UNSIGNED NOT NULL DEFAULT 0,
               PRIMARY KEY  (db, tbl)


             CREATE TABLE IF NOT EXISTS index_usage (
               query_id      BIGINT UNSIGNED NOT NULL,
               db            VARCHAR(64) NOT NULL,
               tbl           VARCHAR(64) NOT NULL,
               idx           VARCHAR(64) NOT NULL,
               cnt           BIGINT UNSIGNED NOT NULL DEFAULT 1,
               UNIQUE INDEX  (query_id, db, tbl, idx)


             CREATE TABLE IF NOT EXISTS index_alternatives (
               query_id      BIGINT UNSIGNED NOT NULL, -- This query used
               db            VARCHAR(64) NOT NULL,     -- this index, but...
               tbl           VARCHAR(64) NOT NULL,     --
               idx           VARCHAR(64) NOT NULL,     --
               alt_idx       VARCHAR(64) NOT NULL,     -- was an alternative
               cnt           BIGINT UNSIGNED NOT NULL DEFAULT 1,
               UNIQUE INDEX  (query_id, db, tbl, idx, alt_idx),
               INDEX         (db, tbl, idx),
               INDEX         (db, tbl, alt_idx)

           The following are some queries you can run against these tables to answer common
           questions you might have.  Each query is also created as a view (with MySQL v5.0 and
           newer) if "--[no]create-views" is true (it is by default).  The view names are the
           strings after the "MAGIC_view_" prefix.

           Question: which queries sometimes use different indexes, and what fraction of the time
           is each index chosen?  MAGIC_view_query_uses_several_indexes:

            SELECT iu.query_id, CONCAT_WS('.', iu.db, iu.tbl, iu.idx) AS idx,
               variations, iu.cnt, iu.cnt / total_cnt * 100 AS pct
            FROM index_usage AS iu
               INNER JOIN (
                  SELECT query_id, db, tbl, SUM(cnt) AS total_cnt,
                    COUNT(*) AS variations
                  FROM index_usage
                  GROUP BY query_id, db, tbl
                  HAVING COUNT(*) > 1
               ) AS qv USING(query_id, db, tbl);

           Question: which indexes have lots of alternatives, i.e. are chosen instead of other
           indexes, and for what queries?  MAGIC_view_index_has_alternates:

            SELECT CONCAT_WS('.', db, tbl, idx) AS idx_chosen,
               GROUP_CONCAT(DISTINCT alt_idx) AS alternatives,
               GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
            FROM index_alternatives
            GROUP BY db, tbl, idx
            HAVING COUNT(*) > 1;

           Question: which indexes are considered as alternates for other indexes, and for what
           queries?  MAGIC_view_index_alternates:

            SELECT CONCAT_WS('.', db, tbl, alt_idx) AS idx_considered,
               GROUP_CONCAT(DISTINCT idx) AS alternative_to,
               GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
            FROM index_alternatives
            GROUP BY db, tbl, alt_idx
            HAVING COUNT(*) > 1;

           Question: which of those are never chosen by any queries, and are therefore
           superfluous?  MAGIC_view_unused_index_alternates:

            SELECT CONCAT_WS('.', i.db, i.tbl, i.idx) AS idx,
               alt.alternative_to, alt.queries, alt.cnt
            FROM indexes AS i
               INNER JOIN (
                  SELECT db, tbl, alt_idx, GROUP_CONCAT(DISTINCT idx) AS alternative_to,
                     GROUP_CONCAT(DISTINCT query_id) AS queries, SUM(cnt) AS cnt
                  FROM index_alternatives
                  GROUP BY db, tbl, alt_idx
                  HAVING COUNT(*) > 1
               ) AS alt ON i.db = alt.db AND i.tbl = alt.tbl
                 AND i.idx = alt.alt_idx
            WHERE i.cnt = 0;

           Question: given a table, which indexes were used, by how many queries, with how many
           distinct fingerprints?  Were there alternatives?  Which indexes were not used?  You
           can edit the following query's SELECT list to also see the query IDs in question.

            SELECT i.idx, iu.usage_cnt, iu.usage_total,
               ia.alt_cnt, ia.alt_total
            FROM indexes AS i
               LEFT OUTER JOIN (
                  SELECT db, tbl, idx, COUNT(*) AS usage_cnt,
                     SUM(cnt) AS usage_total, GROUP_CONCAT(query_id) AS used_by
                  FROM index_usage
                  GROUP BY db, tbl, idx
               ) AS iu ON i.db=iu.db AND i.tbl=iu.tbl AND i.idx = iu.idx
               LEFT OUTER JOIN (
                  SELECT db, tbl, idx, COUNT(*) AS alt_cnt,
                     SUM(cnt) AS alt_total,
                     GROUP_CONCAT(query_id) AS alt_queries
                  FROM index_alternatives
                  GROUP BY db, tbl, idx
               ) AS ia ON i.db=ia.db AND i.tbl=ia.tbl AND i.idx = ia.idx;

           Question: which indexes on a given table are vital for at least one query (there is no
           alternative)?  MAGIC_view_required_indexes:

              SELECT i.db, i.tbl, i.idx, no_alt.queries
              FROM indexes AS i
                 INNER JOIN (
                    SELECT iu.db, iu.tbl, iu.idx,
                       GROUP_CONCAT(iu.query_id) AS queries
                    FROM index_usage AS iu
                       LEFT OUTER JOIN index_alternatives AS ia
                          USING(db, tbl, idx)
                    WHERE ia.db IS NULL
                    GROUP BY iu.db, iu.tbl, iu.idx
                 ) AS no_alt ON no_alt.db = i.db AND no_alt.tbl = i.tbl
                    AND no_alt.idx = i.idx
              ORDER BY i.db, i.tbl, i.idx, no_alt.queries;

           type: Array

           Set the MySQL variables in this comma-separated list of "variable=value" pairs.

           By default, the tool sets:


           Variables specified on the command line override these defaults.  For example,
           specifying "--set-vars wait_timeout=500" overrides the defaultvalue of 10000.

           The tool prints a warning and continues if a variable cannot be set.

           short form: -S; type: string

           Socket file to use for connection.

           short form: -t; type: hash

           Only get indexes from this comma-separated list of tables.

           type: string

           Only get indexes from tables whose names match this Perl regex.

           short form: -u; type: string

           User for login if not current user.

           Show version and exit.

           default: yes

           Check for the latest version of Percona Toolkit, MySQL, and other programs.

           This is a standard "check for updates automatically" feature, with two additional
           features.  First, the tool checks its own version and also the versions of the
           following software: operating system, Percona Monitoring and Management (PMM), MySQL,
           Perl, MySQL driver for Perl (DBD::mysql), and Percona Toolkit. Second, it checks for
           and warns about versions with known problems. For example, MySQL 5.5.25 had a critical
           bug and was re-released as 5.5.25a.

           A secure connection to Percona’s Version Check database server is done to perform
           these checks. Each request is logged by the server, including software version numbers
           and unique ID of the checked system. The ID is generated by the Percona Toolkit
           installation script or when the Version Check database call is done for the first

           Any updates or known problems are printed to STDOUT before the tool's normal output.
           This feature should never interfere with the normal operation of the tool.

           For more information, visit


       These DSN options are used to create a DSN.  Each option is given like "option=value".
       The options are case-sensitive, so P and p are not the same option.  There cannot be
       whitespace before or after the "=" and if the value contains whitespace it must be quoted.
       DSN options are comma-separated.  See the percona-toolkit manpage for full details.

       ·   A

           dsn: charset; copy: yes

           Default character set.

       ·   D

           dsn: database; copy: yes

           Database to connect to.

       ·   F

           dsn: mysql_read_default_file; copy: yes

           Only read default options from the given file

       ·   h

           dsn: host; copy: yes

           Connect to host.

       ·   p

           dsn: password; copy: yes

           Password to use when connecting.  If password contains commas they must be escaped
           with a backslash: "exam\,ple"

       ·   P

           dsn: port; copy: yes

           Port number to use for connection.

       ·   S

           dsn: mysql_socket; copy: yes

           Socket file to use for connection.

       ·   u

           dsn: user; copy: yes

           User for login if not current user.


       The environment variable "PTDEBUG" enables verbose debugging output to STDERR.  To enable
       debugging and capture all output to a file, run the tool like:

          PTDEBUG=1 pt-index-usage ... > FILE 2>&1

       Be careful: debugging output is voluminous and can generate several megabytes of output.


       You need Perl, DBI, DBD::mysql, and some core packages that ought to be installed in any
       reasonably new version of Perl.


       For a list of known bugs, see <>.

       Please report bugs at <>.  Include the following
       information in your bug report:

       ·   Complete command-line used to run the tool

       ·   Tool "--version"

       ·   MySQL version of all servers involved

       ·   Output from the tool including STDERR

       ·   Input files (log/dump/config files, etc.)

       If possible, include debugging output by running the tool with "PTDEBUG"; see


       Visit <> to download the latest release of
       Percona Toolkit.  Or, get the latest release from the command line:




       You can also get individual tools from the latest release:


       Replace "TOOL" with the name of any tool.


       Baron Schwartz and Daniel Nichter


       This tool is part of Percona Toolkit, a collection of advanced command-line tools for
       MySQL developed by Percona.  Percona Toolkit was forked from two projects in June, 2011:
       Maatkit and Aspersa.  Those projects were created by Baron Schwartz and primarily
       developed by him and Daniel Nichter.  Visit <> to learn
       about other free, open-source software from Percona.


       This program is copyright 2011-2018 Percona LLC and/or its affiliates, 2010-2011 Baron


       This program is free software; you can redistribute it and/or modify it under the terms of
       the GNU General Public License as published by the Free Software Foundation, version 2; OR
       the Perl Artistic License.  On UNIX and similar systems, you can issue `man perlgpl' or
       `man perlartistic' to read these licenses.

       You should have received a copy of the GNU General Public License along with this program;
       if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
       MA  02111-1307  USA.


       pt-index-usage 3.0.13


       Hey! The above document had some coding errors, which are explained below:

       Around line 7510:
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