pt-fk-error-logger(1) Log MySQL foreign key errors.


Usage: pt-fk-error-logger [OPTIONS] [DSN]

pt-fk-error-logger logs information about foreign key errors on the given DSN. Information is printed to "STDOUT", and it can also be saved to a table by specifying ``--dest''. The tool runs for forever unless ``--run-time'' or ``--iterations'' is specified.

Print foreign key errors on host1:

pt-fk-error-logger h=host1

Print foreign key errors on host1 once then exit:

   pt-fk-error-logger h=host1 --iterations 1

Save foreign key errors on host1 to percona_schema.fke on host2:

  pt-fk-error-logger h=host1 --dest h=host2,D=percona_schema,t=fke


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


pt-fk-error-logger prints or saves the foreign key errors text from "SHOW INNODB STATUS". The errors are not parsed or interpreted in any way. Foreign key errors are uniquely identified by their timestamp. Only new (more recent) errors are printed or saved.

By default the tool runs forever, checking every ``--interval'' seconds for new foreign key errors. Specify ``--run-time'' and/or ``--iterations'' to limit how long the tool runs.


The foreign key error text from "SHOW ENGINE INNODB STATUS" is printed to "STDOUT", unless ``--quiet'' is specified. Errors and warnings are printed to "STDERR".


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.

Fork to the background and detach from the shell. POSIX operating systems only.
short form: -D; type: string

Connect to this database.

short form: -F; type: string

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

type: DSN

Save foreign key errors in this table. The DSN must specify a database (D) and table (t).

Missing DSN values are inherited from the DSN being monitored, so you can omit most values if you're saving foreign key errors on the same host.

The following table is suggested:

 CREATE TABLE foreign_key_errors (
   ts datetime NOT NULL,
   error text NOT NULL,

The only information saved is the timestamp and the foreign key error text.

Show help and exit.
short form: -h; type: string

Connect to host.

type: time; default: 30

How often to check for foreign key errors.

type: int

How many times to check for foreign key errors. By default, this option is undefined which means an infinite number of iterations. The tool always exits for ``--run-time'', regardless of the value specified for this option. For example, the tool will exit after 1 minute with "--run-time 1m --iterations 4 --interval 30" because 4 iterations at 30 second intervals would take 2 minutes, longer than the 1 mintue run-time.

type: string

Print all output to this file when daemonized.

short form: -p; type: string

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

type: string

Create the given PID file. The tool won't 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.

short form: -P; type: int

Port number to use for connection.

Do not print foreign key errors; only print errors and warnings to "STDERR".
type: time

How long to run before exiting. By default, the tool runs forever.

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: -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 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 <>.


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

    Default database.

  • 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.

  • t

    Table in which to store foreign key errors.

  • 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-fk-error-logger ... > 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 ``ENVIRONMENT''.


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.


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 2011-2016 Percona LLC and/or its affiliates.


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-fk-error-logger 2.2.17