pt-tcp-model

NAME

pt-tcp-model - Transform tcpdump into metrics that permit performance and scalability modeling.

SYNOPSIS

Usage: pt-tcp-model [OPTION...] [FILE]

pt-tcp-model parses and analyzes tcpdump files. With no FILE, or when FILE is -, it read standard input.

Dump TCP requests and responses to a file, capturing only the packet headers to avoid dropped packets, and ignoring any packets without a payload (such as ack-only packets). Capture port 3306 (MySQL database traffic). Note that to avoid line breaking in terminals and man pages, the TCP filtering expression that follows has a line break at the end of the second line; you should omit this from your tcpdump command.

tcpdump -s 384 -i any -nnq -tttt \
      'tcp port 3306 and (((ip[2:2] - ((ip[0]&0xf)<<2))
     - ((tcp[12]&0xf0)>>2)) != 0)' \
  > /path/to/tcp-file.txt

Extract individual response times, sorted by end time:

pt-tcp-model /path/to/tcp-file.txt > requests.txt

Sort the result by arrival time, for input to the next step:

sort -n -k1,1 requests.txt > sorted.txt

Slice the result into 10-second intervals and emit throughput, concurrency, and response time metrics for each interval:

pt-tcp-model --type=requests --run-time=10 sorted.txt > sliced.txt

Transform the result for modeling with Aspersa’s usl tool, discarding the first and last line of each file if you specify multiple files (the first and last line are normally incomplete observation periods and are aberrant):

for f in sliced.txt; do
   tail -n +2 "$f" | head -n -1 | awk '{print $2, $3, $7/$4}'
done > usl-input.txt

RISKS

The following section is included to inform users about the potential risks, whether known or unknown, of using this tool. The two main categories of risks are those created by the nature of the tool (e.g. read-only tools vs. read-write tools) and those created by bugs.

pt-tcp-model merely reads and transforms its input, printing it to the output. It should be very low risk.

At the time of this release, we know of no bugs that could cause serious harm to users.

The authoritative source for updated information is always the online issue tracking system. Issues that affect this tool will be marked as such. You can see a list of such issues at the following URL: http://www.percona.com/bugs/pt-tcp-model.

See also “BUGS” for more information on filing bugs and getting help.

DESCRIPTION

This tool recognizes requests and responses in a TCP stream, and extracts the “conversations”. You can use it to capture the response times of individual queries to a database, for example. It expects the TCP input to be in the following format, which should result from the sample shown in the SYNOPSIS:

<date> <time.microseconds> IP <IP.port> > <IP.port>: <junk>

The tool watches for “incoming” packets to the port you specify with the “–watch-server” option. This begins a request. If multiple inbound packets follow each other, then by default the last inbound packet seen determines the time at which the request is assumed to begin. This is logical if one assumes that a server must receive the whole SQL statement before beginning execution, for example.

When the first outbound packet is seen, the server is considered to have responded to the request. The tool might see an inbound packet, but never see a response. This can happen when the kernel drops packets, for example. As a result, the tool never prints a request unless it sees the response to it. However, the tool actually does not print any request until it sees the “last” outbound packet. It determines this by waiting for either another inbound packet, or EOF, and then considers the previous inbound/outbound pair to be complete. As a result, the tool prints requests in a relatively random order. Most types of analysis require processing in either arrival or completion order. Therefore, the second type of processing this tool can do requires that you sort the output from the first stage and supply it as input.

The second type of processing is selected with the “–type” option set to “requests”. In this mode, the tool reads a group of requests and aggregates them, then emits the aggregated metrics.

OUTPUT

In the default mode (parsing tcpdump output), requests are printed out one per line, in the following format:

<id> <start> <end> <elapsed> <IP:port>

The ID is an incrementing number, assigned in arrival order in the original TCP traffic. The start and end timestamps, and the elapsed time, can be customized with the “–start-end” option.

In “–type=requests” mode, the tool prints out one line per time interval as defined by “–run-time”, with the following columns: ts, concurrency, throughput, arrivals, completions, busy_time, weighted_time, sum_time, variance_mean, quantile_time, obs_time. A detailed explanation follows:

ts

The timestamp that defines the beginning of the interval.

concurrency

The average number of requests resident in the server during the interval.

throughput

The number of arrivals per second during the interval.

arrivals

The number of arrivals during the interval.

completions

The number of completions during the interval.

busy_time

The total amount of time during which at least one request was resident in the server during the interval.

weighted_time

The total response time of all the requests resident in the server during the interval, including requests that neither arrived nor completed during the interval.

sum_time

The total response time of all the requests that arrived in the interval.

variance_mean

The variance-to-mean ratio (index of dispersion) of the response times of the requests that arrived in the interval.

quantile_time

The Nth percentile response time for all the requests that arrived in the interval. See also “–quantile”.

obs_time

The length of the observation time window. This will usually be the same as the interval length, except for the first and last intervals in a file, which might have a shorter observation time.

OPTIONS

This tool accepts additional command-line arguments. Refer to the “SYNOPSIS” and usage information for details.

--config

type: Array

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

--help Show help and exit.
--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.

--quantile

type: float

The percentile for the last column when “–type” is “requests” (default .99).

--run-time

type: float

The size of the aggregation interval in seconds when “–type” is “requests” (default 1). Fractional values are permitted.

--start-end

type: Array; default: ts,end

Define how the arrival and completion timestamps of a query, and thus its response time (elapsed time) are computed. Recall that there may be multiple inbound and outbound packets per request and response, and refer to the following ASCII diagram. Suppose that a client sends a series of three inbound (I) packets to the server, whch computes the result and then sends two outbound (O) packets back:

I I    I ..................... O    O
|<---->|<---response time----->|<-->|
ts0    ts                      end  end1

By default, the query is considered to arrive at time ts, and complete at time end. However, this might not be what you want. Perhaps you do not want to consider the query to have completed until time end1. You can accomplish this by setting this option to ts,end1.

--type

type: string

The type of input to parse (default tcpdump). The permitted types are

tcpdump

The parser expects the input to be formatted with the following options: -x -n -q -tttt. For example, if you want to capture output from your local machine, you can do something like the following (the port must come last on FreeBSD):

tcpdump -s 65535 -x -nn -q -tttt -i any -c 1000 port 3306 \
  > mysql.tcp.txt
pt-query-digest --type tcpdump mysql.tcp.txt

The other tcpdump parameters, such as -s, -c, and -i, are up to you. Just make sure the output looks like this (there is a line break in the first line to avoid man-page problems):

2009-04-12 09:50:16.804849 IP 127.0.0.1.42167
       > 127.0.0.1.3306: tcp 37

All MySQL servers running on port 3306 are automatically detected in the tcpdump output. Therefore, if the tcpdump out contains packets from multiple servers on port 3306 (for example, 10.0.0.1:3306, 10.0.0.2:3306, etc.), all packets/queries from all these servers will be analyzed together as if they were one server.

If you’re analyzing traffic for a protocol that is not running on port 3306, see “–watch-server”.

--version Show version and exit.
--watch-server

type: string; default: 10.10.10.10:3306

This option tells pt-tcp-model which server IP address and port (such as “10.0.0.1:3306”) to watch when parsing tcpdump for “–type” tcpdump. If you don’t specify it, the tool watches all servers by looking for any IP address using port 3306. If you’re watching a server with a non-standard port, this won’t work, so you must specify the IP address and port to watch.

Currently, IP address filtering isn’t implemented; so even though you must specify the option in IP:port form, it ignores the IP and only looks at the port number.

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-tcp-model ... > 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-tcp-model.

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

ABOUT PERCONA TOOLKIT

This tool is part of Percona Toolkit, a collection of advanced command-line tools developed by Percona for MySQL support and consulting. Percona Toolkit was forked from two projects in June, 2011: Maatkit and Aspersa. Those projects were created by Baron Schwartz and developed primarily by him and Daniel Nichter, both of whom are employed by Percona. Visit http://www.percona.com/software/ for more software developed by Percona.

VERSION

pt-tcp-model 1.0.2

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