|o||Read the tools documentation|
|o||Review the tools known BUGS|
|o||Test the tool on a non-production server|
|o||Backup your production server and verify the backups|
pt-table-usage reads queries from a log and analyzes how they use tables. The log should be in MySQLs slow query log format.
Table usage is more than simply an indication of which tables the query reads or writes. It also indicates data flow: data in and data out. The tool determines the data flow by the contexts in which tables appear. A single query can use a table in several different contexts simultaneously. The tools output lists every context for every table. This CONTEXT-TABLE list indicates how data flows between tables. The OUTPUT section lists the possible contexts and describes how to read a table usage report.
The tool analyzes data flow down to the level of individual columns, so it is helpful if columns are identified unambiguously in the query. If a query uses only one table, then all columns must be from that table, and theres no difficulty. But if a query uses multiple tables and the column names are not table-qualified, then it is necessary to use EXPLAIN EXTENDED, followed by SHOW WARNINGS, to determine to which tables the columns belong.
If the tool does not know the querys default database, which can occur when the database is not printed in the log, then EXPLAIN EXTENDED can fail. In this case, you can specify a default database with --database. You can also use the --create-table-definitions option to help resolve ambiguities.
The tool prints a usage report for each table in every query, similar to the following:
Query_id: 0x1CD27577D202A339.1 UPDATE t1 SELECT DUAL JOIN t1 JOIN t2 WHERE t1 Query_id: 0x1CD27577D202A339.2 UPDATE t2 SELECT DUAL JOIN t1 JOIN t2 WHERE t1
The first line contains the query ID, which by default is the same as those shown in pt-query-digest reports. It is an MD5 checksum of the querys fingerprint, which is what remains after removing literals, collapsing white space, and a variety of other transformations. The query ID has two parts separated by a period: the query ID and the table number. If you wish to use a different value to identify the query, you can specify the --id-attribute option.
The previous example shows two paragraphs for a single query, not two queries. Note that the query ID is identical for the two, but the table number differs. The table number increments by 1 for each table that the query updates. Only multi-table UPDATE queries can update multiple tables with a single query, so the table number is 1 for all other types of queries. (The tool does not support multi-table DELETE queries.) The example output above is from this query:
UPDATE t1 AS a JOIN t2 AS b USING (id) SET a.foo="bar", b.foo="bat" WHERE a.id=1;
After the first line, the tool prints a variable number of CONTEXT-TABLE lines. Possible contexts are as follows:
SELECT means that the query retrieves data from the table for one of two reasons. The first is to be returned to the user as part of a result set. Only SELECT queries return result sets, so the report always shows a SELECT context for SELECT queries.
The second case is when data flows to another table as part of an INSERT or UPDATE. For example, the UPDATE query in the example above has the usage:
This refers to:
SET a.foo="bar", b.foo="bat"
The tool uses DUAL for any values that do not originate in a table, in this case the literal values bar and bat. If that SET clause were SET a.foo=b.foo instead, then the complete usage would be:
Query_id: 0x1CD27577D202A339.1 UPDATE t1 SELECT t2 JOIN t1 JOIN t2 WHERE t1
The presence of a SELECT context after another context, such as UPDATE or INSERT, indicates where the UPDATE or INSERT retrieves its data. The example immediately above reflects an UPDATE query that updates rows in table t1 with data from table t2.
o Any other verb
Any other verb, such as INSERT, UPDATE, DELETE, etc. may be a context. These verbs indicate that the query modifies data in some way. If a SELECT context follows one of these verbs, then the query reads data from the SELECT table and writes it to this table. This happens, for example, with INSERT..SELECT or UPDATE queries that use values from tables instead of constant values.
These query types are not supported: SET, LOAD, and multi-table DELETE.
The JOIN context lists tables that are joined, either with an explicit JOIN in the FROM clause, or implicitly in the WHERE clause, such as t1.id = t2.id.
The WHERE context lists tables that are used in the WHERE clause to filter results. This does not include tables that are implicitly joined in the WHERE clause; those are listed as JOIN contexts. For example:
WHERE t1.id > 100 AND t1.id < 200 AND t2.foo IS NOT NULL
WHERE t1 WHERE t2
The tool lists only distinct tables; that is why table t1 is listed only once.
The TLIST context lists tables that the query accesses, but which do not appear in any other context. These tables are usually an implicit cartesian join. For example, the query SELECT * FROM t1, t2 results in:
Query_id: 0xBDDEB6EDA41897A8.1 SELECT t1 SELECT t2 TLIST t1 TLIST t2
First of all, there are two SELECT contexts, because SELECT * selects rows from all tables; t1 and t2 in this case. Secondly, the tables are implicitly joined, but without any kind of join condition, which results in a cartesian join as indicated by the TLIST context for each.
pt-table-usage exits 1 on any kind of error, or 0 if no errors.
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 Perls 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.
--constant-data-value type: string; default: DUAL
Table to print as the source for constant data (literals). This is any data not retrieved from tables (or subqueries, because subqueries are not supported). This includes literal values such as strings (foo) and numbers (42), or functions such as NOW(). For example, in the query INSERT INTO t (c) VALUES (a), the string a is constant data, so the table usage report is:
INSERT t SELECT DUAL
The first line indicates that the query inserts data into table t, and the second line indicates that the inserted data comes from some constant value.
--[no]continue-on-error default: yes
Continue to work even if there is an error.
--create-table-definitions type: array
Read CREATE TABLE definitions from this list of comma-separated files. If you cannot use --explain-extended to fully qualify table and column names, you can save the output of mysqldump --no-data to one or more files and specify those files with this option. The tool will parse all CREATE TABLE definitions from the files and use this information to qualify table and column names. If a column name appears in multiple tables, or a table name appears in multiple databases, the ambiguities cannot be resolved.
--daemonize Fork to the background and detach from the shell. POSIX operating systems only. --database short form: -D; type: string
--defaults-file short form: -F; type: string
Only read mysql options from the given file. You must give an absolute pathname.
--explain-extended type: DSN
A server to execute EXPLAIN EXTENDED queries. This may be necessary to resolve ambiguous (unqualified) column and table names.
--filter type: string
Discard events for which this Perl code doesnt return true.
This option is a string of Perl code or a file containing Perl code that is compiled into a subroutine with one argument: $event. If the given value is a readable file, then pt-table-usage reads the entire file and uses its contents as the code.
Filters are implemented in the same fashion as in the pt-query-digest tool, so please refer to its documentation for more information.
--help Show help and exit. --host short form: -h; type: string
Connect to host.
--id-attribute type: string
Identify each event using this attribute. The default is to use a query ID, which is an MD5 checksum of the querys fingerprint.
--log type: string
Print all output to this file when daemonized.
--password short form: -p; type: string
Password to use when connecting.
--pid type: string
Create the given PID file. The tool wont start if the PID file already exists and the PID it contains is different than the current PID. However, if the PID file exists and the PID it contains is no longer running, the tool will overwrite the PID file with the current PID. The PID file is removed automatically when the tool exits.
--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.
--query type: string
Analyze the specified query instead of reading a log file.
--read-timeout type: time; default: 0
Wait this long for an event from the input; 0 to wait forever.
This option sets the maximum time to wait for an event from the input. If an event is not received after the specified time, the tool stops reading the input and prints its reports.
This option requires the Perl POSIX module.
--run-time type: time
How long to run before exiting. The default is to run forever (you can interrupt with CTRL-C).
--set-vars 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.
--socket short form: -S; type: string
Socket file to use for connection.
--user short form: -u; type: string --version Show version and exit.
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.
dsn: charset; copy: yes
Default character set.
dsn: mysql_read_default_file; copy: no
Only read default options from the given file
dsn: host; copy: yes
Connect to host.
dsn: password; copy: yes
Password to use when connecting.
dsn: port; copy: yes
Port number to use for connection.
dsn: mysql_socket; copy: no
Socket file to use for connection.
dsn: user; copy: yes
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-table-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 <http://www.percona.com/bugs/pt-table-usage>.
Please report bugs at <https://bugs.launchpad.net/percona-toolkit>. Include the following information in your bug report:
If possible, include debugging output by running the tool with PTDEBUG; see ENVIRONMENT.
o Complete command-line used to run the tool o Tool --version o MySQL version of all servers involved o Output from the tool including STDERR o Input files (log/dump/config files, etc.)
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:
Replace TOOL with the name of any tool.
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.
This program is copyright 2012-2015 Percona LLC and/or its affiliates.
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.
|perl v5.20.3||PT-TABLE-USAGE (1)||2015-04-10|