| PT-STALK(1p) | User Contributed Perl Documentation | PT-STALK(1p) |
pt-stalk - Collect forensic data about MySQL when problems occur.
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.
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:
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.
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.
Collect diagnostic data when the trigger occurs. Specify "--no-collect" to make the tool watch the system but not collect data.
See also "--stalk".
In addition to freezing the server, there is also some risk of the server crashing or performing badly after GDB detaches from it.
Read this comma-separated list of config files. If specified, this must be the first option on the command line.
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.
Only read mysql options from the given file. You must give an absolute pathname.
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.
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.
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.
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:
Watch "SHOW GLOBAL STATUS" for the trigger. The value of "--variable" then defines which status counter is the trigger.
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.
Host to connect to.
How often to check the if trigger is true, in seconds.
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.
Print all output to this file when daemonized.
The pattern to use when watching SHOW PROCESSLIST. See "--function" for details.
Send an email to these addresses for every "--collect".
Password to use when connecting. If password contains commas they must be escaped with a backslash: "exam\,ple"
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.
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:
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 number to use for connection.
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.
Keep the data for the last N runs. If N > 0, the program will keep the data for the last N runs and will delete the older data.
Keep up to --retention-size MB of data. It will keep at least 1 run even if the size is bigger than the specified in this parameter
Number of days to retain collected samples. Any samples that are older will be purged.
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.
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.
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 file to use for connection.
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.
See also "--collect".
The maximum acceptable value for "--variable". "--collect" is triggered when the value of "--variable" is greater than "--threshold" for "--cycles" many times. Currently, there is no way to define a lower threshold to check for a "--variable" value that is too low.
See also "--function".
User for login if not current user.
The variable to compare against "--threshold". See also "--function".
Print more or less information while running. Since the tool is designed to be a long-running daemon, the default verbosity level only prints the most important information. If you run the tool interactively, you may want to use a higher verbosity level.
LEVEL PRINTS
===== =====================================
0 Errors
1 Warnings
2 Matching triggers and collection info
3 Non-matching triggers
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:
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.
It is possible to enable "debug" mode in mysqladmin specifying:
"CMD_MYSQLADMIN='mysqladmin debug' pt-stalk params ..."
This tool requires Bash v3 or newer. Certain options require other programs:
For a list of known bugs, see <http://www.percona.com/bugs/pt-stalk>.
Please report bugs at <https://jira.percona.com/projects/PT>. Include the following information in your bug report:
If possible, include debugging output by running the tool with "PTDEBUG"; see "ENVIRONMENT".
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.
Baron Schwartz, Justin Swanhart, Fernando Ipar, Daniel Nichter, and Brian Fraser
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 2011-2018 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.
pt-stalk 3.2.1
| 2020-08-30 | perl v5.30.3 |