Ubuntu Manpage: pt-stalk - Collect forensic data about MySQL when problems occur.

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NAME

       pt-stalk - Collect forensic data about MySQL when problems occur.

SYNOPSIS

       Usage: pt-stalk [OPTIONS]

       pt-stalk waits for a trigger condition to occur, then collects data to help diagnose problems.  The tool
       is designed to run as a daemon with root privileges, so that you can diagnose intermittent problems that
       you cannot observe directly.  You can also use it to execute a custom command, or to collect data on
       demand without waiting for the trigger to occur.

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

Sometimes a problem happens infrequently and for a short time, giving you no chance to see the system
when it happens. How do you solve intermittent MySQL problems when you can't observe them? That's why pt-
stalk exists. In addition to using it when there's a known problem on your servers, it is a good idea to
run pt-stalk all the time, even when you think nothing is wrong. You will appreciate the data it
collects when a problem occurs, because problems such as MySQL lockups or spikes in activity typically
leave no evidence to use in root cause analysis.

pt-stalk does two things: it watches a MySQL server and waits for a trigger condition to occur, and it
collects diagnostic data when that trigger occurs. To avoid false-positives caused by short-lived
problems, the trigger condition must be true at least "--cycles" times before a "--collect" is triggered.

To use pt-stalk effectively, you need to define a good trigger. A good trigger is sensitive enough to
fire reliably when a problem occurs, so that you don't miss a chance to solve problems. On the other
hand, a good trigger isn't prone to false positives, so you don't gather information when the server is
functioning normally.

The most reliable triggers for MySQL tend to be the number of connections to the server, and the number
of queries running concurrently. These are available in the SHOW GLOBAL STATUS command as
Threads_connected and Threads_running. Sometimes Threads_connected is not a reliable indicator of
trouble, but Threads_running usually is. Your job, as the tool's user, is to define an appropriate
trigger condition for the tool. Choose carefully, because the quality of your results will depend on the
trigger you choose.

You define the trigger with the "--function", "--variable", "--threshold", and "--cycles" options. The
default values for these options define a reasonable trigger, but you should adjust or change them to
suite your particular system and needs.

By default, pt-stalk tool watches MySQL forever until the trigger occurs, then it collects diagnostic
data for a while, and sleeps afterwards to avoid repeatedly collecting data if the trigger remains true.
The general order of operations is:

while true; do
if --variable from --function > --threshold; then
cycles_true++
if cycles_true >= --cycles; then
--notify-by-email
if --collect; then
if --disk-bytes-free and --disk-pct-free ok; then
(--collect for --run-time seconds) &
fi
rm files in --dest older than --retention-time
fi
iter++
cycles_true=0
fi
if iter < --iterations; then
sleep --sleep seconds
else
break
fi
else
if iter < --iterations; then
sleep --interval seconds
else
break
fi
fi
done
rm old --dest files older than --retention-time
if --collect process are still running; then
wait up to --run-time * 3 seconds
kill any remaining --collect processes
fi

The diagnostic data is written to files whose names begin with a timestamp, so you can distinguish
samples from each other in case the tool collects data multiple times. The pt-sift tool is designed to
help you browse and analyze the resulting data samples.

Although this sounds simple enough, in practice there are a number of subtleties, such as detecting when
the disk is beginning to fill up so that the tool doesn't cause the server to run out of disk space.
This tool handles these types of potential problems, so it's a good idea to use this tool instead of
writing something from scratch and possibly experiencing some of the hazards this tool is designed to
avoid.

CONFIGURING

       You can use standard Percona Toolkit configuration files to set command line options.

       You will probably want to run the tool as a daemon and customize at least the "--threshold".  Here's a
       sample configuration file for triggering when there are more than 20 queries running at once:

         daemonize
         threshold=20

       If you don't run the tool as root, then you will need specify several options, such as "--pid", "--log",
       and "--dest", else the tool will probably fail to start.

OPTIONS

--ask-pass
Prompt for a password when connecting to MySQL.

--collect
default: yes; negatable: yes

Collect diagnostic data when the trigger occurs. Specify "--no-collect" to make the tool watch the
system but not collect data.

See also "--stalk".

--collect-gdb
Collect GDB stacktraces. This is achieved by attaching to MySQL and printing stack traces from all
threads. This will freeze the server for some period of time, ranging from a second or so to much
longer on very busy systems with a lot of memory and many threads in the server. For this reason, it
is disabled by default. However, if you are trying to diagnose a server stall or lockup, freezing the
server causes no additional harm, and the stack traces can be vital for diagnosis.

In addition to freezing the server, there is also some risk of the server crashing or performing
badly after GDB detaches from it.

--collect-oprofile
Collect oprofile data. This is achieved by starting an oprofile session, letting it run for the
collection time, and then stopping and saving the resulting profile data in the system's default
location. Please read your system's oprofile documentation to learn more about this.

--collect-strace
Collect strace data. This is achieved by attaching strace to the server, which will make it run very
slowly until strace detaches. The same cautions apply as those listed in --collect-gdb. You should
not enable this option together with --collect-gdb, because GDB and strace can't attach to the server
process simultaneously.

--collect-tcpdump
Collect tcpdump data. This option causes tcpdump to capture all traffic on all interfaces for the
port on which MySQL is listening. You can later use pt-query-digest to decode the MySQL protocol and
extract a log of query traffic from it.

--config
type: string

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

--cycles
type: int; default: 5

How many times "--variable" must be greater than "--threshold" before triggering "--collect". This
helps prevent false positives, and makes the trigger condition less likely to fire when the problem
recovers quickly.

--daemonize
Daemonize the tool. This causes the tool to fork into the background and log its output as specified
in --log.

--defaults-file
short form: -F; type: string

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

--dest
type: string; default: /var/lib/pt-stalk

Where to save diagnostic data from "--collect". Each time the tool collects data, it writes to a new
set of files, which are named with the current system timestamp.

--disk-bytes-free
type: size; default: 100M

Do not "--collect" if the disk has less than this much free space. This prevents the tool from
filling up the disk with diagnostic data.

If the "--dest" directory contains a previously captured sample of data, the tool will measure its
size and use that as an estimate of how much data is likely to be gathered this time, too. It will
then be even more pessimistic, and will refuse to collect data unless the disk has enough free space
to hold the sample and still have the desired amount of free space. For example, if you'd like 100MB
of free space and the previous diagnostic sample consumed 100MB, the tool won't collect any data
unless the disk has 200MB free.

Valid size value suffixes are k, M, G, and T.

--disk-pct-free
type: int; default: 5

Do not "--collect" if the disk has less than this percent free space. This prevents the tool from
filling up the disk with diagnostic data.

This option works similarly to "--disk-bytes-free" but specifies a percentage margin of safety
instead of a bytes margin of safety. The tool honors both options, and will not collect any data
unless both margins are satisfied.

--function
type: string; default: status

What to watch for the trigger. The default value watches "SHOW GLOBAL STATUS", but you can also
watch "SHOW PROCESSLIST" and specify a file with your own custom code. This function supplies the
value of "--variable", which is then compared against "--threshold" to see if the the trigger
condition is met. Additional options may be required as well; see below. Possible values are:

• status

Watch "SHOW GLOBAL STATUS" for the trigger. The value of "--variable" then defines which status
counter is the trigger.

• processlist

Watch "SHOW FULL PROCESSLIST" for the trigger. The trigger value is the count of processes whose
"--variable" column matches the "--match" option. For example, to trigger "--collect" when more
than 10 processes are in the "statistics" state, specify:

--function processlist \
--variable State \
--match statistics \
--threshold 10

In addition, you can specify a file that contains your custom trigger function, written in Unix shell
script. This can be a wrapper that executes anything you wish. If the argument to "--function" is a
file, then it takes precedence over built-in functions, so if there is a file in the working
directory named "status" or "processlist" then the tool will use that file even though are valid
built-in values.

The file works by providing a function called "trg_plugin", and the tool simply sources the file and
executes the function. For example, the file might contain:

trg_plugin() {
mysql $EXT_ARGV -e "SHOW ENGINE INNODB STATUS" \
| grep -c "has waited at"
}

This snippet will count the number of mutex waits inside InnoDB. It illustrates the general
principle: the function must output a number, which is then compared to "--threshold" as usual. The
$EXT_ARGV variable contains the MySQL options mentioned in the "SYNOPSIS" above.

The file should not alter the tool's existing global variables. Prefix any file-specific global
variables with "PLUGIN_" or make them local.

--help
Print help and exit.

--host
short form: -h; type: string

Host to connect to.

--interval
type: int; default: 1

How often to check the if trigger is true, in seconds.

--iterations
type: int

How many times to "--collect" diagnostic data. By default, the tool runs forever and collects data
every time the trigger occurs. Specify "--iterations" to collect data a limited number of times.
This option is also useful with "--no-stalk" to collect data once and exit, for example.

--log
type: string; default: /var/log/pt-stalk.log

Print all output to this file when daemonized.

--match
type: string

The pattern to use when watching SHOW PROCESSLIST. See "--function" for details.

--notify-by-email
type: string

Send an email to these addresses for every "--collect".

--password
short form: -p; type: string

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

--pid
type: string; default: /var/run/pt-stalk.pid

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.

--plugin
type: string

Load a plugin to hook into the tool and extend is functionality. The specified file does not need to
be executable, nor does its first line need to be shebang line. It only needs to define one or more
of these Bash functions:

before_stalk
Called before stalking.

before_collect
Called when the trigger occurs, before running a "--collect" subprocesses in the background.

after_collect
Called after running a collector process. The PID of the collector process is passed as the
first argument. This hook is called before "after_collect_sleep".

after_collect_sleep
Called after sleeping "--sleep" seconds for the collector process to finish. This hook is called
after "after_collect".

after_interval_sleep
Called after sleeping "--interval" seconds after each trigger check.

after_stalk
Called after stalking. Since pt-stalk stalks forever by default, this hook is only called if
"--iterations" is specified.

For example, a very simple plugin that touches a file when "--collect" is triggered:

before_collect() {
touch /tmp/foo
}

Since the plugin is completely sourced (imported) into the tool's namespace, be careful not to define
other functions or global variables that already exist in the tool. You should prefix all plugin-
specific functions and global variables with "plugin_" or "PLUGIN_".

Plugins have access to all command line options but they should not modify them. Each option is a
global variable like $OPT_DEST which corresponds to "--dest". Therefore, the global variable for
each command line option is "OPT_" plus the option name in all caps with hyphens replaced by
underscores.

Plugins can stop the tool by setting the global variable "OKTORUN" to 1. In this case, the global
variable "EXIT_REASON" should also be set to indicate why the tool was stopped.

Plugin writers should keep in mind that the file destination prefix currently in use should be
accessed through the $prefix variable, rather than $OPT_PREFIX.

--port
short form: -P; type: int

Port number to use for connection.

--prefix
type: string

The filename prefix for diagnostic samples. By default, all files created by the same "--collect"
instance have a timestamp prefix based on the current local time, like "2011_12_06_14_02_02", which
is December 6, 2011 at 14:02:02.

--retention-time
type: int; default: 30

Number of days to retain collected samples. Any samples that are older will be purged.

--run-time
type: int; default: 30

How long to "--collect" diagnostic data when the trigger occurs. The value is in seconds and should
not be longer than "--sleep". It is usually not necessary to change this; if the default 30 seconds
doesn't collect enough data, running longer is not likely to help because the system or MySQL server
is probably too busy to respond. In fact, in many cases a shorter collection period is appropriate.

This value is used two other times. After collecting, the collect subprocess will wait another
"--run-time" seconds for its commands to finish. Some commands can take awhile if the system is
running very slowly (which can likely be the case given that a collection was triggered). Since
empty files are deleted, the extra wait gives commands time to finish and write their data. The
value is potentially used again just before the tool exits to wait again for any collect subprocesses
to finish. In most cases this won't happen because of the aforementioned extra wait. If it happens,
the tool will log "Waiting up to N seconds for subprocesses to finish..." where N is three times
"--run-time". In both cases, after waiting, the tool kills all of its subprocesses.

--sleep
type: int; default: 300

How long to sleep after "--collect". This prevents the tool from triggering continuously, which
might be a problem if the collection process is intrusive. It also prevents filling up the disk or
gathering too much data to analyze reasonably.

--sleep-collect
type: int; default: 1

How long to sleep between collection loop cycles. This is useful with "--no-stalk" to do long
collections. For example, to collect data every minute for an hour, specify: "--no-stalk --run-time
3600 --sleep-collect 60".

--socket
short form: -S; type: string

Socket file to use for connection.

--stalk
default: yes; negatable: yes

Watch the server and wait for the trigger to occur. Specify "--no-stalk" to collect diagnostic data
immediately, that is, without waiting for the trigger to occur. You probably also want to specify
values for "--interval", "--iterations", and "--sleep". For example, to immediately collect data for
1 minute then exit, specify:

--no-stalk --run-time 60 --iterations 1

"--cycles", "--daemonize", "--log" and "--pid" have no effect with "--no-stalk". Safeguard options,
like "--disk-bytes-free" and "--disk-pct-free", are still respected.

ENVIRONMENT

       This tool does not require any environment variables for configuration, although it can be influenced to
       work differently by through several variables.  Keep in mind that these are expert settings, and should
       not be used in most cases.

       Specifically, the variables that can be set are:

       CMD_GDB
       CMD_IOSTAT
       CMD_MPSTAT
       CMD_MYSQL
       CMD_MYSQLADMIN
       CMD_OPCONTROL
       CMD_OPREPORT
       CMD_PMAP
       CMD_STRACE
       CMD_SYSCTL
       CMD_TCPDUMP
       CMD_VMSTAT

       For example, during collection iostat is called with a -dx argument, but because you have an NFS
       partition, you also need the -n flag there.  Instead of editing the source, you can call pt-stalk as

           CMD_IOSTAT="iostat -n" pt-stalk ...

       which will do exactly what you need.  Combined with the plugin hooks, this gives you a fine-grained
       control of what the tool does.

SYSTEM REQUIREMENTS

       This tool requires Bash v3 or newer.  Certain options require other programs:

       "--collect-gdb" requires "gdb"
       "--collect-oprofile" requires "opcontrol" and "opreport"
       "--collect-strace" requires "strace"
       "--collect-tcpdump" requires "tcpdump"

BUGS

       For a list of known bugs, see <http://www.percona.com/bugs/pt-stalk>.

       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, Justin Swanhart, Fernando Ipar, Daniel Nichter, and Brian Fraser

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.

VERSION

       pt-stalk 2.2.16