NAME¶
pt-index-usage - Read queries from a log and analyze how they use indexes.
SYNOPSIS¶
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
RISKS¶
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, please:
- •
- 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
DESCRIPTION¶
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 useful.
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 measure.
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!
OUTPUT¶
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 error.
OPTIONS¶
This tool accepts additional command-line arguments. Refer to the
"SYNOPSIS" and usage information for details.
- --ask-pass
- Prompt for a password when connecting to MySQL.
- --charset
- 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.
- --config
- type: Array
Read this comma-separated list of config files; if specified, this must be
the first option on the command line.
- --create-save-results-database
- 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.
- --[no]create-views
- 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.
- --database
- short form: -D; type: string
The database to use for the connection.
- --databases
- short form: -d; type: hash
Only get tables and indexes from this comma-separated list of
databases.
- --databases-regex
- type: string
Only get tables and indexes from database whose names match this Perl
regex.
- --defaults-file
- short form: -F; type: string
Only read mysql options from the given file. You must give an absolute
pathname.
- --drop
- 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.
- --empty-save-results-tables
- 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.
- --help
- Show help and exit.
- --host
- short form: -h; type: string
Connect to host.
- --ignore-databases
- type: Hash
Ignore this comma-separated list of databases.
- --ignore-databases-regex
- type: string
Ignore databases whose names match this Perl regex.
- --ignore-tables
- type: Hash
Ignore this comma-separated list of table names.
Table names may be qualified with the database name.
- --ignore-tables-regex
- type: string
Ignore tables whose names match the Perl regex.
- --password
- short form: -p; type: string
Password to use when connecting.
- --port
- short form: -P; type: int
Port number to use for connection.
- --progress
- 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.
- --quiet
- short form: -q
Do not print any warnings. Also disables "--progress".
- --[no]report
- 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 later.
- --report-format
- 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".
- --save-results-database
- 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 USE'ed.
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:
MAGIC_create_indexes:
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)
)
MAGIC_create_queries:
CREATE TABLE IF NOT EXISTS queries (
query_id BIGINT UNSIGNED NOT NULL,
fingerprint TEXT NOT NULL,
sample TEXT NOT NULL,
PRIMARY KEY (query_id)
)
MAGIC_create_tables:
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)
)
MAGIC_create_index_usage:
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)
)
MAGIC_create_index_alternatives:
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. MAGIC_view_index_usage:
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;
- --set-vars
- type: Array
Set the MySQL variables in this comma-separated list of
"variable=value" pairs.
By default, the tool sets:
wait_timeout=10000
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.
- --socket
- short form: -S; type: string
Socket file to use for connection.
- --tables
- short form: -t; type: hash
Only get indexes from this comma-separated list of tables.
- --tables-regex
- type: string
Only get indexes from tables whose names match this Perl regex.
- --user
- short form: -u; type: string
User for login if not current user.
- --version
- Show version and exit.
- --[no]version-check
- 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 the version of other
programs on the local system in addition to its own version. For example,
it checks the version of every MySQL server it connects to, Perl, and the
Perl module DBD::mysql. 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.
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
<https://www.percona.com/version-check>.
DSN OPTIONS¶
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.
- •
- 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.
ENVIRONMENT¶
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.
SYSTEM REQUIREMENTS¶
You need Perl, DBI, DBD::mysql, and some core packages that ought to be
installed in any reasonably new version of Perl.
BUGS¶
For a list of known bugs, see
<
http://www.percona.com/bugs/pt-index-usage>.
Please report bugs at <
https://bugs.launchpad.net/percona-toolkit>.
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 "ENVIRONMENT".
DOWNLOADING¶
Visit <
http://www.percona.com/software/percona-toolkit/> to download the
latest release of Percona Toolkit. Or, get the latest release from the command
line:
wget percona.com/get/percona-toolkit.tar.gz
wget percona.com/get/percona-toolkit.rpm
wget percona.com/get/percona-toolkit.deb
You can also get individual tools from the latest release:
wget percona.com/get/TOOL
Replace "TOOL" with the name of any tool.
AUTHORS¶
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
<
http://www.percona.com/software/> to learn about other free,
open-source software from Percona.
COPYRIGHT, LICENSE, AND WARRANTY¶
This program is copyright 2011-2014 Percona LLC and/or its affiliates, 2010-2011
Baron Schwartz.
THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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.
VERSION¶
pt-index-usage 2.2.11