PT-INDEX-USAGE(1) User Contributed Perl Documentation PT-INDEX-USAGE(1)NAMEpt-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
ABOUT PERCONA TOOLKIT
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 2011-2015 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.
VERSIONpt-index-usage 2.2.14
perl v5.20.2 2015-04-10 PT-INDEX-USAGE(1)
