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mk-query-digest.1p - Man Page

Analyze query execution logs and generate a query report, filter, replay, or transform queries for MySQL, PostgreSQL, memcached, and more.


Usage: mk-query-digest [OPTION...] [FILE]

mk-query-digest parses and analyzes MySQL log files.  With no FILE, or when FILE is -, it read standard input.

Analyze, aggregate, and report on a slow query log:

 mk-query-digest /path/to/slow.log

Review a slow log, saving results to the test.query_review table in a MySQL server running on host1.  See "--review" for more on reviewing queries:

 mk-query-digest --review h=host1,D=test,t=query_review /path/to/slow.log

Filter out everything but SELECT queries, replay the queries against another server, then use the timings from replaying them to analyze their performance:

 mk-query-digest /path/to/slow.log --execute h=another_server \
   --filter '$event->{fingerprint} =~ m/^select/'

Print the structure of events so you can construct a complex "--filter":

 mk-query-digest /path/to/slow.log --no-report \
   --filter 'print Dumper($event)'

Watch SHOW FULL PROCESSLIST and output a log in slow query log format:

 mk-query-digest --processlist h=host1 --print --no-report

The default aggregation and analysis is CPU and memory intensive.  Disable it if you don't need the default report:

 mk-query-digest <arguments> --no-report


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.

By default mk-query-digest merely collects and aggregates data from the files specified.  It is designed to be as efficient as possible, but depending on the input you give it, it can use a lot of CPU and memory.  Practically speaking, it is safe to run even on production systems, but you might want to monitor it until you are satisfied that the input you give it does not cause undue load.

Various options will cause mk-query-digest to insert data into tables, execute SQL queries, and so on.  These include the "--execute" option and "--review".

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.maatkit.org/bugs/mk-query-digest>.

See also "Bugs" for more information on filing bugs and getting help.


This tool was formerly known as mk-log-parser.

mk-query-digest is a framework for doing things with events from a query source such as the slow query log or PROCESSLIST.  By default it acts as a very sophisticated log analysis tool.  You can group and sort queries in many different ways simultaneously and find the most expensive queries, or create a timeline of queries in the log, for example.  It can also do a "query review," which means to save a sample of each type of query into a MySQL table so you can easily see whether you've reviewed and analyzed a query before.  The benefit of this is that you can keep track of changes to your server's queries and avoid repeated work.  You can also save other information with the queries, such as comments, issue numbers in your ticketing system, and so on.

Note that this is a work in *very* active progress and you should expect incompatible changes in the future.


mk-query-digest works on events, which are a collection of key/value pairs called attributes.  You'll recognize most of the attributes right away: Query_time, Lock_time, and so on.  You can just look at a slow log and see them. However, there are some that don't exist in the slow log, and slow logs may actually include different kinds of attributes (for example, you may have a server with the Percona patches).

For a full list of attributes, see <http://code.google.com/p/maatkit/wiki/EventAttributes>.

With creative use of "--filter", you can create new attributes derived from existing attributes.  For example, to create an attribute called Row_ratio for examining the ratio of Rows_sent to Rows_examined, specify a filter like:

  --filter '($event->{Row_ratio} = $event->{Rows_sent} / ($event->{Rows_examined})) && 1'

The && 1 trick is needed to create a valid one-line syntax that is always true, even if the assignment happens to evaluate false.  The new attribute will automatically appears in the output:

  # Row ratio           1.00    0.00       1    0.50       1    0.71    0.50

Attributes created this way can be specified for "--order-by" or any option that requires an attribute.


memcached events have additional attributes related to the memcached protocol: cmd, key, res (result) and val.  Also, boolean attributes are created for the various commands, misses and errors: Memc_CMD where CMD is a memcached command (get, set, delete, etc.), Memc_error and Memc_miss.

These attributes are no different from slow log attributes, so you can use them with "--[no]report", "--group-by", in a "--filter", etc.

These attributes and more are documented at <http://code.google.com/p/maatkit/wiki/EventAttributes>.


The default output is a query analysis report.  The "--[no]report" option controls whether or not this report is printed.  Sometimes you may wish to parse all the queries but suppress the report, for example when using "--print", "--review" or "--save-results".

There is one paragraph for each class of query analyzed.  A "class" of queries all have the same value for the "--group-by" attribute which is "fingerprint" by default.  (See "Attributes".)  A fingerprint is an abstracted version of the query text with literals removed, whitespace collapsed, and so forth.  The report is formatted so it's easy to paste into emails without wrapping, and all non-query lines begin with a comment, so you can save it to a .sql file and open it in your favorite syntax-highlighting text editor.  There is a response-time profile at the beginning.

The output described here is controlled by "--report-format". That option allows you to specify what to print and in what order. The default output in the default order is described here.

The report, by default, begins with a paragraph about the entire analysis run The information is very similar to what you'll see for each class of queries in the log, but it doesn't have some information that would be too expensive to keep globally for the analysis.  It also has some statistics about the code's execution itself, such as the CPU and memory usage, the local date and time of the run, and a list of input file read/parsed.

Following this is the response-time profile over the events.  This is a highly summarized view of the unique events in the detailed query report that follows.  It contains the following columns:

 Column        Meaning
 ============  ==========================================================
 Rank          The query's rank within the entire set of queries analyzed
 Query ID      The query's fingerprint
 Response time The total response time, and percentage of overall total
 Calls         The number of times this query was executed
 R/Call        The mean response time per execution
 Apdx          The Apdex score; see --apdex-threshold for details
 V/M           The Variance-to-mean ratio of response time
 EXPLAIN       If --explain was specified, a sparkline; see --explain
 Item          The distilled query

A final line whose rank is shown as MISC contains aggregate statistics on the queries that were not included in the report, due to options such as "--limit" and "--outliers".  For details on the variance-to-mean ratio, please see http://en.wikipedia.org/wiki/Index_of_dispersion.

Next, the detailed query report is printed.  Each query appears in a paragraph. Here is a sample, slightly reformatted so 'perldoc' will not wrap lines in a terminal.  The following will all be one paragraph, but we'll break it up for commentary.

 # Query 2: 0.01 QPS, 0.02x conc, ID 0xFDEA8D2993C9CAF3 at byte 160665

This line identifies the sequential number of the query in the sort order specified by "--order-by".  Then there's the queries per second, and the approximate concurrency for this query (calculated as a function of the timespan and total Query_time).  Next there's a query ID.  This ID is a hex version of the query's checksum in the database, if you're using "--review".  You can select the reviewed query's details from the database with a query like SELECT .... WHERE checksum=0xFDEA8D2993C9CAF3.

If you are investigating the report and want to print out every sample of a particular query, then the following "--filter" may be helpful: mk-query-digest slow-log.log --no-report --print --filter '$event-{fingerprint}  && make_checksum($event->{fingerprint}) eq "FDEA8D2993C9CAF3"'>.

Notice that you must remove the 0x prefix from the checksum in order for this to work.

Finally, in case you want to find a sample of the query in the log file, there's the byte offset where you can look.  (This is not always accurate, due to some silly anomalies in the slow-log format, but it's usually right.)  The position refers to the worst sample, which we'll see more about below.

Next is the table of metrics about this class of queries.

 #           pct   total    min    max     avg     95%  stddev  median
 # Count       0       2
 # Exec time  13   1105s   552s   554s    553s    554s      2s    553s
 # Lock time   0   216us   99us  117us   108us   117us    12us   108us
 # Rows sent  20   6.26M  3.13M  3.13M   3.13M   3.13M   12.73   3.13M
 # Rows exam   0   6.26M  3.13M  3.13M   3.13M   3.13M   12.73   3.13M

The first line is column headers for the table.  The percentage is the percent of the total for the whole analysis run, and the total is the actual value of the specified metric.  For example, in this case we can see that the query executed 2 times, which is 13% of the total number of queries in the file.  The min, max and avg columns are self-explanatory.  The 95% column shows the 95th percentile; 95% of the values are less than or equal to this value.  The standard deviation shows you how tightly grouped the values are.  The standard deviation and median are both calculated from the 95th percentile, discarding the extremely large values.

The stddev, median and 95th percentile statistics are approximate.  Exact statistics require keeping every value seen, sorting, and doing some calculations on them.  This uses a lot of memory.  To avoid this, we keep 1000 buckets, each of them 5% bigger than the one before, ranging from .000001 up to a very big number.  When we see a value we increment the bucket into which it falls.  Thus we have fixed memory per class of queries.  The drawback is the imprecision, which typically falls in the 5 percent range.

Next we have statistics on the users, databases and time range for the query.

 # Users       1   user1
 # Databases   2     db1(1), db2(1)
 # Time range 2008-11-26 04:55:18 to 2008-11-27 00:15:15

The users and databases are shown as a count of distinct values, followed by the values.  If there's only one, it's shown alone; if there are many, we show each of the most frequent ones, followed by the number of times it appears.

 # Query_time distribution
 #   1us
 #  10us
 # 100us
 #   1ms
 #  10ms
 # 100ms
 #    1s
 #  10s+  #############################################################

The execution times show a logarithmic chart of time clustering.  Each query goes into one of the "buckets" and is counted up.  The buckets are powers of ten.  The first bucket is all values in the "single microsecond range" -- that is, less than 10us.  The second is "tens of microseconds," which is from 10us up to (but not including) 100us; and so on.  The charted attribute can be changed by specifying "--report-histogram" but is limited to time-based attributes.

 # Tables
 #    SHOW CREATE TABLE `table1`\G
 SELECT * FROM table1\G

This section is a convenience: if you're trying to optimize the queries you see in the slow log, you probably want to examine the table structure and size. These are copy-and-paste-ready commands to do that.

Finally, we see a sample of the queries in this class of query.  This is not a random sample.  It is the query that performed the worst, according to the sort order given by "--order-by".  You will normally see a commented # EXPLAIN line just before it, so you can copy-paste the query to examine its EXPLAIN plan. But for non-SELECT queries that isn't possible to do, so the tool tries to transform the query into a roughly equivalent SELECT query, and adds that below.

If you want to find this sample event in the log, use the offset mentioned above, and something like the following:

  tail -c +<offset> /path/to/file | head

See also "--report-format".


The output also contains sparklines.  Sparklines are "data-intense, design-simple, word-sized graphics" (<http://en.wikipedia.org/wiki/Sparkline>).There is a sparkline for "--report-histogram" and for "--explain". See each of those options for details about interpreting their sparklines.

Query Reviews

A "query review" is the process of storing all the query fingerprints analyzed. This has several benefits:

To use this feature, you run mk-query-digest with the "--review" option.  It will store the fingerprints and other information into the table you specify. Next time you run it with the same option, it will do the following:


A query fingerprint is the abstracted form of a query, which makes it possible to group similar queries together.  Abstracting a query removes literal values, normalizes whitespace, and so on.  For example, consider these two queries:

  SELECT name, password FROM user WHERE id='12823';
  select name,   password from user
     where id=5;

Both of those queries will fingerprint to

  select name, password from user where id=?

Once the query's fingerprint is known, we can then talk about a query as though it represents all similar queries.

What mk-query-digest does is analogous to a GROUP BY statement in SQL.  (But note that "multiple columns" doesn't define a multi-column grouping; it defines multiple reports!) If your command-line looks like this,

  mk-query-digest /path/to/slow.log --select Rows_read,Rows_sent \
      --group-by fingerprint --order-by Query_time:sum --limit 10

The corresponding pseudo-SQL looks like this:

  SELECT WORST(query BY Query_time), SUM(Query_time), ...
  FROM /path/to/slow.log
  ORDER BY SUM(Query_time) DESC
  LIMIT 10

You can also use the value distill, which is a kind of super-fingerprint. See "--group-by" for more.

When parsing memcached input ("--type" memcached), the fingerprint is an abstracted version of the command and key, with placeholders removed.  For example, "get user_123_preferences" fingerprints to "get user_?_preferences". There is also a "key_print" which a fingerprinted version of the key.  This example's key_print is "user_?_preferences".

Query fingerprinting accommodates a great many special cases, which have proven necessary in the real world.  For example, an IN list with 5 literals is really equivalent to one with 4 literals, so lists of literals are collapsed to a single one.  If you want to understand more about how and why all of these cases are handled, please review the test cases in the Subversion repository.  If you find something that is not fingerprinted properly, please submit a bug report with a reproducible test case.  Here is a list of transformations during fingerprinting, which might not be exhaustive:


DSN values in "--review-history" default to values in "--review" if COPY is yes.

This tool accepts additional command-line arguments.  Refer to the "Synopsis" and usage information for details.


type: float; default: 1.0

Set Apdex target threshold (T) for query response time.  The Application Performance Index (Apdex) Technical Specification V1.1 defines T as "a positive decimal value in seconds, having no more than two significant digits of granularity."  This value only applies to query response time (Query_time).

Options can be abbreviated so specifying --apdex-t also works.

See <http://www.apdex.org/>.


Prompt for a password when connecting to MySQL.


type: array; default: db|Schema

List of attribute|alias,etc.

Certain attributes have multiple names, like db and Schema.  If an event does not have the primary attribute, mk-query-digest looks for an alias attribute. If it finds an alias, it creates the primary attribute with the alias attribute's value and removes the alias attribute.

If the event has the primary attribute, all alias attributes are deleted.

This helps simplify event attributes so that, for example, there will not be report lines for both db and Schema.


type: int; default: 4294967296

A sanity limit for attribute values.

This option deals with bugs in slow-logging functionality that causes large values for attributes.  If the attribute's value is bigger than this, the last-seen value for that class of query is used instead.


type: DSN

Auxiliary DSN used for special options.

The following options may require a DSN even when only parsing a slow log file:

  * --since
  * --until

See each option for why it might require a DSN.


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: int; default: 1000

Stop checking for new attributes after this many events.

For better speed, mk-query-digest stops checking events for new attributes after a certain number of events.  Any new attributes after this number will be ignored and will not be reported.

One special case is new attributes for pre-existing query classes (see "--group-by" about query classes).  New attributes will not be added to pre-existing query classes even if the attributes are detected before the "--check-attributes-limit" limit.


type: Array

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


default: yes

Continue parsing even if there is an error.


Create the "--review-history" table if it does not exist.

This option causes the table specified by "--review-history" to be created with the default structure shown in the documentation for that option.


Create the "--review" table if it does not exist.

This option causes the table specified by "--review" to be created with the default structure shown in the documentation for that option.


Fork to the background and detach from the shell.  POSIX operating systems only.


short form: -F; type: string

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


type: array

Two Perl regex patterns to capture pseudo-attributes embedded in queries.

Embedded attributes might be special attribute-value pairs that you've hidden in comments.  The first regex should match the entire set of attributes (in case there are multiple).  The second regex should match and capture attribute-value pairs from the first regex.

For example, suppose your query looks like the following:

  SELECT * from users -- file: /login.php, line: 493;

You might run mk-query-digest with the following option:

  mk-query-digest --embedded-attributes ' -- .*','(\w+): ([^\,]+)'

The first regular expression captures the whole comment:

  " -- file: /login.php, line: 493;"

The second one splits it into attribute-value pairs and adds them to the event:

   =========  ==========
   file       /login.php
   line       493

NOTE: All commas in the regex patterns must be escaped with \ otherwise the pattern will break.


type: DSN

Execute queries on this DSN.

Adds a callback into the chain, after filters but before the reports.  Events are executed on this DSN.  If they are successful, the time they take to execute overwrites the event's Query_time attribute and the original Query_time value (from the log) is saved as the Exec_orig_time attribute.  If unsuccessful, the callback returns false and terminates the chain.

If the connection fails, mk-query-digest tries to reconnect once per second.

See also "--mirror" and "--execute-throttle".


type: array

Throttle values for "--execute".

By default "--execute" runs without any limitations or concerns for the amount of time that it takes to execute the events.  The "--execute-throttle" allows you to limit the amount of time spent doing "--execute" relative to the other processes that handle events.  This works by marking some events with a Skip_exec attribute when "--execute" begins to take too much time. "--execute" will not execute an event if this attribute is true.  This indirectly decreases the time spent doing "--execute".

The "--execute-throttle" option takes at least two comma-separated values: max allowed "--execute" time as a percentage and a check interval time.  An optional third value is a percentage step for increasing and decreasing the probability that an event will be marked Skip_exec true.  5 (percent) is the default step.

For example: "--execute-throttle" 70,60,10.  This will limit "--execute" to 70% of total event processing time, checked every minute (60 seconds) and probability stepped up and down by 10%.  When "--execute" exceeds 70%, the probability that events will be marked Skip_exec true increases by 10%. "--execute" time is checked again after another minute. If it's still above 70%, then the probability will increase another 10%. Or, if it's dropped below 70%, then the probability will decrease by 10%.


type: array; default: 5,10

Explain items when there are more or fewer than expected.

Defines the number of items expected to be seen in the report given by "--[no]report", as controlled by "--limit" and "--outliers".  If there  are more or fewer items in the report, each one will explain why it was included.


type: DSN

Run EXPLAIN for the sample query with this DSN and print results.

This works only when "--group-by" includes fingerprint.  It causes mk-query-digest to run EXPLAIN and include the output into the report.  For safety, queries that appear to have a subquery that EXPLAIN will execute won't be EXPLAINed.  Those are typically "derived table" queries of the form

  select ... from ( select .... ) der;

The EXPLAIN results are printed in three places: a sparkline in the event header, a full vertical format in the event report, and a sparkline in the profile.

The full format appears at the end of each event report in vertical style (\G) just like MySQL prints it.

The sparklines (see "Sparklines") are compact representations of the access type for each table and whether or not "Using temporary" or "Using filesort" appear in EXPLAIN.  The sparklines look like:


That sparkline means that there are two tables, the first uses a range (n) access, the second uses a ref access, and both "Using temporary" (T) and "Using filesort" (F) appear.  The greater-than character just separates table access codes from T and/or F.

The abbreviated table access codes are:

  a  ALL
  c  const
  e  eq_ref
  f  fulltext
  i  index
  m  index_merge
  n  range
  o  ref_or_null
  r  ref
  s  system
  u  unique_subquery

A capitalized access code means that "Using index" appears in EXPLAIN for that table.


type: string

Discard events for which this Perl code doesn't return true.

This option is a string of Perl code or a file containing Perl code that gets compiled into a subroutine with one argument: $event.  This is a hashref. If the given value is a readable file, then mk-query-digest reads the entire file and uses its contents as the code.  The file should not contain a shebang (#!/usr/bin/perl) line.

If the code returns true, the chain of callbacks continues; otherwise it ends. The code is the last statement in the subroutine other than return $event.  The subroutine template is:

  sub { $event = shift; filter && return $event; }

Filters given on the command line are wrapped inside parentheses like like ( filter ).  For complex, multi-line filters, you must put the code inside a file so it will not be wrapped inside parentheses.  Either way, the filter must produce syntactically valid code given the template.  For example, an if-else branch given on the command line would not be valid:

  --filter 'if () { } else { }'  # WRONG

Since it's given on the command line, the if-else branch would be wrapped inside parentheses which is not syntactically valid.  So to accomplish something more complex like this would require putting the code in a file, for example filter.txt:

  my $event_ok; if (...) { $event_ok=1; } else { $event_ok=0; } $event_ok

Then specify --filter filter.txt to read the code from filter.txt.

If the filter code won't compile, mk-query-digest will die with an error. If the filter code does compile, an error may still occur at runtime if the code tries to do something wrong (like pattern match an undefined value). mk-query-digest does not provide any safeguards so code carefully!

An example filter that discards everything but SELECT statements:

  --filter '$event->{arg} =~ m/^select/i'

This is compiled into a subroutine like the following:

  sub { $event = shift; ( $event->{arg} =~ m/^select/i ) && return $event; }

It is permissible for the code to have side effects (to alter $event).

You can find an explanation of the structure of $event at <http://code.google.com/p/maatkit/wiki/EventAttributes>.

Here are more examples of filter code:

Host/IP matches domain.com

--filter '($event->{host} || $event->{ip} || "") =~ m/domain.com/'

Sometimes MySQL logs the host where the IP is expected.  Therefore, we check both.

User matches john

--filter '($event->{user} || "") =~ m/john/'

More than 1 warning

--filter '($event->{Warning_count} || 0) > 1'

Query does full table scan or full join

--filter '(($event->{Full_scan} || "") eq "Yes") || (($event->{Full_join} || "") eq "Yes")'

Query was not served from query cache

--filter '($event->{QC_Hit} || "") eq "No"'

Query is 1 MB or larger

--filter '$event->{bytes} >= 1_048_576'

Since "--filter" allows you to alter $event, you can use it to do other things, like create new attributes.  See "Attributes" for an example.


Add query fingerprints to the standard query analysis report.  This is mostly useful for debugging purposes.


default: yes

Print extra information to make analysis easy.

This option adds code snippets to make it easy to run SHOW CREATE TABLE and SHOW TABLE STATUS for the query's tables.  It also rewrites non-SELECT queries into a SELECT that might be helpful for determining the non-SELECT statement's index usage.


type: Array; default: fingerprint

Which attribute of the events to group by.

In general, you can group queries into classes based on any attribute of the query, such as user or db, which will by default show you which users and which databases get the most Query_time.  The default attribute, fingerprint, groups similar, abstracted queries into classes; see below and see also "Fingerprints".

A report is printed for each "--group-by" value (unless --no-report is given).  Therefore, --group-by user,db means "report on queries with the same user and report on queries with the same db"--it does not mean "report on queries with the same user and db."  See also "Output".

Every value must have a corresponding value in the same position in "--order-by".  However, adding values to "--group-by" will automatically add values to "--order-by", for your convenience.

There are several magical values that cause some extra data mining to happen before the grouping takes place:


This causes events to be fingerprinted to abstract queries into a canonical form, which is then used to group events together into a class. See "Fingerprints" for more about fingerprinting.


This causes events to be inspected for what appear to be tables, and then aggregated by that.  Note that a query that contains two or more tables will be counted as many times as there are tables; so a join against two tables will count the Query_time against both tables.


This is a sort of super-fingerprint that collapses queries down into a suggestion of what they do, such as INSERT SELECT table1 table2.

If parsing memcached input ("--type" memcached), there are other attributes which you can group by: key_print (see memcached section in "Fingerprints"), cmd, key, res and val (see memcached section in "Attributes").


default: yes

Gzip "--save-results" files; requires IO::Compress::Gzip.


Show help and exit.


short form: -h; type: string

Connect to host.


type: array; default: arg, cmd, insert_id, ip, port, Thread_id, timestamp, exptime, flags, key, res, val, server_id, offset, end_log_pos, Xid

Do not aggregate these attributes when auto-detecting "--select".

If you do not specify "--select" then mk-query-digest auto-detects and aggregates every attribute that it finds in the slow log.  Some attributes, however, should not be aggregated.  This option allows you to specify a list of attributes to ignore.  This only works when no explicit "--select" is given.


type: array; default: db,ts

If missing, inherit these attributes from the last event that had them.

This option sets which attributes are inherited or carried forward to events which do not have them.  For example, if one event has the db attribute equal to "foo", but the next event doesn't have the db attribute, then it inherits "foo" for its db attribute.

Inheritance is usually desirable, but in some cases it might confuse things. If a query inherits a database that it doesn't actually use, then this could confuse "--execute".


type: float; default: .1

How frequently to poll the processlist, in seconds.


type: int; default: 1

How many times to iterate through the collect-and-report cycle.  If 0, iterate to infinity.  Each iteration runs for "--run-time" amount of time.  An iteration is usually determined by an amount of time and a report is printed when that amount of time elapses.  With "--run-time-mode" interval, an interval is instead determined by the interval time you specify with "--run-time".  See "--run-time" and "--run-time-mode" for more information.


type: Array; default: 95%:20

Limit output to the given percentage or count.

If the argument is an integer, report only the top N worst queries.  If the argument is an integer followed by the % sign, report that percentage of the worst queries.  If the percentage is followed by a colon and another integer, report the top percentage or the number specified by that integer, whichever comes first.

The value is actually a comma-separated array of values, one for each item in "--group-by".  If you don't specify a value for any of those items, the default is the top 95%.

See also "--outliers".


type: string

Print all output to this file when daemonized.


type: float

How often to check whether connections should be moved, depending on read_only.  Requires "--processlist" and "--execute".

This option causes mk-query-digest to check every N seconds whether it is reading from a read-write server and executing against a read-only server, which is a sensible way to set up two servers if you're doing something like master-master replication.  The <http://code.google.com/p/mysql-master-master/> master-master toolkit does this. The aim is to keep the passive server ready for failover, which is impossible without putting it under a realistic workload.


type: Array; default: Query_time:sum

Sort events by this attribute and aggregate function.

This is a comma-separated list of order-by expressions, one for each "--group-by" attribute.  The default Query_time:sum is used for "--group-by" attributes without explicitly given "--order-by" attributes (that is, if you specify more "--group-by" attributes than corresponding "--order-by" attributes).  The syntax is attribute:aggregate.  See "Attributes" for valid attributes.  Valid aggregates are:

   Aggregate Meaning
   ========= ============================
   sum       Sum/total attribute value
   min       Minimum attribute value
   max       Maximum attribute value
   cnt       Frequency/count of the query

For example, the default Query_time:sum means that queries in the query analysis report will be ordered (sorted) by their total query execution time ("Exec time").  Query_time:max orders the queries by their maximum query execution time, so the query with the single largest Query_time will be list first.  cnt refers more to the frequency of the query as a whole, how often it appears; "Count" is its corresponding line in the query analysis report.  So any attribute and cnt should yield the same report wherein queries are sorted by the number of times they appear.

When parsing general logs ("--type" genlog), the default "--order-by" becomes Query_time:cnt.  General logs do not report query times so only the cnt aggregate makes sense because all query times are zero.

If you specify an attribute that doesn't exist in the events, then mk-query-digest falls back to the default Query_time:sum and prints a notice at the beginning of the report for each query class.  You can create attributes with "--filter" and order by them; see "Attributes" for an example.


type: array; default: Query_time:1:10

Report outliers by attribute:percentile:count.

The syntax of this option is a comma-separated list of colon-delimited strings. The first field is the attribute by which an outlier is defined.  The second is a number that is compared to the attribute's 95th percentile.  The third is optional, and is compared to the attribute's cnt aggregate.  Queries that pass this specification are added to the report, regardless of any limits you specified in "--limit".

For example, to report queries whose 95th percentile Query_time is at least 60 seconds and which are seen at least 5 times, use the following argument:

  --outliers Query_time:60:5

You can specify an --outliers option for each value in "--group-by".


short form: -p; type: string

Password to use when connecting.


type: string

Create the given PID file when daemonized.  The file contains the process ID of the daemonized instance.  The PID file is removed when the daemonized instance exits.  The program checks for the existence of the PID file when starting; if it exists and the process with the matching PID exists, the program exits.


Print a profile of the pipeline processes.


short form: -P; type: int

Port number to use for connection.


Print log events to STDOUT in standard slow-query-log format.


Print the start time for each "--iterations".

This option causes a line like the following to be printed at the start of each "--iterations" report:

  # Iteration 2 started at 2009-11-24T14:39:48.345780

This line will print even if --no-report is specified.  If --iterations 0 is specified, each iteration number will be 0.


type: DSN

Poll this DSN's processlist for queries, with "--interval" sleep between.

If the connection fails, mk-query-digest tries to reopen it once per second. See also "--mirror".


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.


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.  It applies to all types of input except "--processlist".  If an event is not received after the specified time, the script stops reading the input and prints its reports.  If "--iterations" is 0 or greater than 1, the next iteration will begin, else the script will exit.

This option requires the Perl POSIX module.


default: yes

Print out reports on the aggregate results from "--group-by".

This is the standard slow-log analysis functionality.  See "Output" for the description of what this does and what the results look like.


Include all queries, even if they have already been reviewed.


type: Array; default: rusage,date,hostname,files,header,profile,query_report,prepared

Print these sections of the query analysis report.

  ============ ======================================================
  rusage       CPU times and memory usage reported by ps
  date         Current local date and time
  hostname     Hostname of machine on which mk-query-digest was run
  files        Input files read/parse
  header       Summary of the entire analysis run
  profile      Compact table of queries for an overview of the report
  query_report Detailed information about each unique query
  prepared     Prepared statements

The sections are printed in the order specified.  The rusage, date, files and header sections are grouped together if specified together; other sections are separated by blank lines.

See "Output" for more information on the various parts of the query report.


type: string; default: Query_time

Chart the distribution of this attribute's values.

The distribution chart is limited to time-based attributes, so charting Rows_examined, for example, will produce a useless chart.  Charts look like:

  # Query_time distribution
  #   1us
  #  10us
  # 100us
  #   1ms
  #  10ms  ################################
  # 100ms  ################################################################
  #    1s  ########
  #  10s+

A sparkline (see "Sparklines") of the full chart is also printed in the header for each query event.  The sparkline of that full chart is:

  # Query_time sparkline: |    .^_ |

The sparkline itself is the 8 characters between the pipes (|), one character for each of the 8 buckets (1us, 10us, etc.)  Four character codes are used to represent the approximate relation between each bucket's value:

  _ . - ^

The caret ^ represents peaks (buckets with the most values), and the underscore _ represents lows (buckets with the least or at least one value).  The period . and the hyphen - represent buckets with values between these two extremes.  If a bucket has no values, a space is printed. So in the example above, the period represents the 10ms bucket, the caret the 100ms bucket, and the underscore the 1s bucket.

See "Output" for more information.


type: DSN

Store a sample of each class of query in this DSN.

The argument specifies a table to store all unique query fingerprints in.  The table must have at least the following columns.  You can add more columns for your own special purposes, but they won't be used by mk-query-digest.  The following CREATE TABLE definition is also used for "--create-review-table". MAGIC_create_review:

  CREATE TABLE query_review (
     fingerprint  TEXT NOT NULL,
     sample       TEXT NOT NULL,
     first_seen   DATETIME,
     last_seen    DATETIME,
     reviewed_by  VARCHAR(20),
     reviewed_on  DATETIME,
     comments     TEXT

The columns are as follows:

  ===========  ===============
  checksum     A 64-bit checksum of the query fingerprint
  fingerprint  The abstracted version of the query; its primary key
  sample       The query text of a sample of the class of queries
  first_seen   The smallest timestamp of this class of queries
  last_seen    The largest timestamp of this class of queries
  reviewed_by  Initially NULL; if set, query is skipped thereafter
  reviewed_on  Initially NULL; not assigned any special meaning
  comments     Initially NULL; not assigned any special meaning

Note that the fingerprint column is the true primary key for a class of queries.  The checksum is just a cryptographic hash of this value, which provides a shorter value that is very likely to also be unique.

After parsing and aggregating events, your table should contain a row for each fingerprint.  This option depends on --group-by fingerprint (which is the default).  It will not work otherwise.


type: DSN

The table in which to store historical values for review trend analysis.

Each time you review queries with "--review", mk-query-digest will save information into this table so you can see how classes of queries have changed over time.

This DSN inherits unspecified values from "--review".  It should mention a table in which to store statistics about each class of queries.  mk-query-digest verifies the existence of the table, and your privileges to insert, delete and update on that table.

mk-query-digest then inspects the columns in the table.  The table must have at least the following columns:

  CREATE TABLE query_review_history (
    checksum     BIGINT UNSIGNED NOT NULL,
    sample       TEXT NOT NULL

Any columns not mentioned above are inspected to see if they follow a certain naming convention.  The column is special if the name ends with an underscore followed by any of these MAGIC_history_cols values:


If the column ends with one of those values, then the prefix is interpreted as the event attribute to store in that column, and the suffix is interpreted as the metric to be stored.  For example, a column named Query_time_min will be used to store the minimum Query_time for the class of events.  The presence of this column will also add Query_time to the "--select" list.

The table should also have a primary key, but that is up to you, depending on how you want to store the historical data.  We suggest adding ts_min and ts_max columns and making them part of the primary key along with the checksum.  But you could also just add a ts_min column and make it a DATE type, so you'd get one row per class of queries per day.

The default table structure follows.  The following MAGIC_create_review_history table definition is used for "--create-review-history-table":

 CREATE TABLE query_review_history (
   checksum             BIGINT UNSIGNED NOT NULL,
   sample               TEXT NOT NULL,
   ts_min               DATETIME,
   ts_max               DATETIME,
   ts_cnt               FLOAT,
   Query_time_sum       FLOAT,
   Query_time_min       FLOAT,
   Query_time_max       FLOAT,
   Query_time_pct_95    FLOAT,
   Query_time_stddev    FLOAT,
   Query_time_median    FLOAT,
   Lock_time_sum        FLOAT,
   Lock_time_min        FLOAT,
   Lock_time_max        FLOAT,
   Lock_time_pct_95     FLOAT,
   Lock_time_stddev     FLOAT,
   Lock_time_median     FLOAT,
   Rows_sent_sum        FLOAT,
   Rows_sent_min        FLOAT,
   Rows_sent_max        FLOAT,
   Rows_sent_pct_95     FLOAT,
   Rows_sent_stddev     FLOAT,
   Rows_sent_median     FLOAT,
   Rows_examined_sum    FLOAT,
   Rows_examined_min    FLOAT,
   Rows_examined_max    FLOAT,
   Rows_examined_pct_95 FLOAT,
   Rows_examined_stddev FLOAT,
   Rows_examined_median FLOAT,
   -- Percona extended slowlog attributes 
   -- http://www.percona.com/docs/wiki/patches:slow_extended
   Rows_affected_sum             FLOAT,
   Rows_affected_min             FLOAT,
   Rows_affected_max             FLOAT,
   Rows_affected_pct_95          FLOAT,
   Rows_affected_stddev          FLOAT,
   Rows_affected_median          FLOAT,
   Rows_read_sum                 FLOAT,
   Rows_read_min                 FLOAT,
   Rows_read_max                 FLOAT,
   Rows_read_pct_95              FLOAT,
   Rows_read_stddev              FLOAT,
   Rows_read_median              FLOAT,
   Merge_passes_sum              FLOAT,
   Merge_passes_min              FLOAT,
   Merge_passes_max              FLOAT,
   Merge_passes_pct_95           FLOAT,
   Merge_passes_stddev           FLOAT,
   Merge_passes_median           FLOAT,
   InnoDB_IO_r_ops_min           FLOAT,
   InnoDB_IO_r_ops_max           FLOAT,
   InnoDB_IO_r_ops_pct_95        FLOAT,
   InnoDB_IO_r_ops_stddev        FLOAT,
   InnoDB_IO_r_ops_median        FLOAT,
   InnoDB_IO_r_bytes_min         FLOAT,
   InnoDB_IO_r_bytes_max         FLOAT,
   InnoDB_IO_r_bytes_pct_95      FLOAT,
   InnoDB_IO_r_bytes_stddev      FLOAT,
   InnoDB_IO_r_bytes_median      FLOAT,
   InnoDB_IO_r_wait_min          FLOAT,
   InnoDB_IO_r_wait_max          FLOAT,
   InnoDB_IO_r_wait_pct_95       FLOAT,
   InnoDB_IO_r_wait_stddev       FLOAT,
   InnoDB_IO_r_wait_median       FLOAT,
   InnoDB_rec_lock_wait_min      FLOAT,
   InnoDB_rec_lock_wait_max      FLOAT,
   InnoDB_rec_lock_wait_pct_95   FLOAT,
   InnoDB_rec_lock_wait_stddev   FLOAT,
   InnoDB_rec_lock_wait_median   FLOAT,
   InnoDB_queue_wait_min         FLOAT,
   InnoDB_queue_wait_max         FLOAT,
   InnoDB_queue_wait_pct_95      FLOAT,
   InnoDB_queue_wait_stddev      FLOAT,
   InnoDB_queue_wait_median      FLOAT,
   InnoDB_pages_distinct_min     FLOAT,
   InnoDB_pages_distinct_max     FLOAT,
   InnoDB_pages_distinct_pct_95  FLOAT,
   InnoDB_pages_distinct_stddev  FLOAT,
   InnoDB_pages_distinct_median  FLOAT,
   -- Boolean (Yes/No) attributes.  Only the cnt and sum are needed for these.
   -- cnt is how many times is attribute was recorded and sum is how many of
   -- those times the value was Yes.  Therefore sum/cnt * 100 = % of recorded
   -- times that the value was Yes.
   QC_Hit_cnt          FLOAT,
   QC_Hit_sum          FLOAT,
   Full_scan_cnt       FLOAT,
   Full_scan_sum       FLOAT,
   Full_join_cnt       FLOAT,
   Full_join_sum       FLOAT,
   Tmp_table_cnt       FLOAT,
   Tmp_table_sum       FLOAT,
   Disk_tmp_table_cnt  FLOAT,
   Disk_tmp_table_sum  FLOAT,
   Filesort_cnt        FLOAT,
   Filesort_sum        FLOAT,
   Disk_filesort_cnt   FLOAT,
   Disk_filesort_sum   FLOAT,
   PRIMARY KEY(checksum, ts_min, ts_max)

Note that we store the count (cnt) for the ts attribute only; it will be redundant to store this for other attributes.


type: time

How long to run for each "--iterations".  The default is to run forever (you can interrupt with CTRL-C).  Because "--iterations" defaults to 1, if you only specify "--run-time", mk-query-digest runs for that amount of time and then exits.  The two options are specified together to do collect-and-report cycles.  For example, specifying "--iterations" 4 "--run-time" 15m with a continuous input (like STDIN or "--processlist") will cause mk-query-digest to run for 1 hour (15 minutes x 4), reporting four times, once at each 15 minute interval.


type: string; default: clock

Set what the value of "--run-time" operates on.  Following are the possible values for this option:


"--run-time" specifies an amount of real clock time during which the tool should run for each "--iterations".


"--run-time" specifies an amount of log time.  Log time is determined by timestamps in the log.  The first timestamp seen is remembered, and each timestamp after that is compared to the first to determine how much log time has passed.  For example, if the first timestamp seen is 12:00:00 and the next is 12:01:30, that is 1 minute and 30 seconds of log time.  The tool will read events until the log time is greater than or equal to the specified "--run-time" value.

Since timestamps in logs are not always printed, or not always printed frequently, this mode varies in accuracy.


"--run-time" specifies interval boundaries of log time into which events are divided and reports are generated.  This mode is different from the others because it doesn't specify how long to run.  The value of "--run-time" must be an interval that divides evenly into minutes, hours or days.  For example, 5m divides evenly into hours (60/5=12, so 12 5 minutes intervals per hour) but 7m does not (60/7=8.6).

Specifying --run-time-mode interval --run-time 30m --iterations 0 is similar to specifying --run-time-mode clock --run-time 30m --iterations 0. In the latter case, mk-query-digest will run forever, producing reports every 30 minutes, but this only works effectively with  continuous inputs like STDIN and the processlist.  For fixed inputs, like log files, the former example produces multiple reports by dividing the log into 30 minutes intervals based on timestamps.

Intervals are calculated from the zeroth second/minute/hour in which a timestamp occurs, not from whatever time it specifies.  For example, with 30 minute intervals and a timestamp of 12:10:30, the interval is not 12:10:30 to 12:40:30, it is 12:00:00 to 12:29:59. Or, with 1 hour intervals, it is 12:00:00 to 12:59:59. When a new timestamp exceeds the interval, a report is printed, and the next interval is recalculated based on the new timestamp.

Since "--iterations" is 1 by default, you probably want to specify a new value else mk-query-digest will only get and report on the first interval from the log since 1 interval = 1 iteration.  If you want to get and report every interval in a log, specify "--iterations" 0.


type: int

Filter out all but the first N occurrences of each query.  The queries are filtered on the first value in "--group-by", so by default, this will filter by query fingerprint.  For example, --sample 2 will permit two sample queries for each fingerprint.  Useful in conjunction with "--print" to print out the queries.  You probably want to set --no-report to avoid the overhead of aggregating and reporting if you're just using this to print out samples of queries.  A complete example:

  mk-query-digest --sample 2 --no-report --print slow.log

type: string

Save results to the specified file.

If "--[no]gzip" is true (by default it is) then .gz is appended to the file name.


type: Array

Compute aggregate statistics for these attributes.

By default mk-query-digest auto-detects, aggregates and prints metrics for every query attribute that it finds in the slow query log.  This option specifies a list of only the attributes that you want.  You can specify an alternative attribute with a colon.  For example, db:Schema uses db if it's available, and Schema if it's not.

Previously, mk-query-digest only aggregated these attributes:


Attributes specified in the "--review-history" table will always be selected  even if you do not specify "--select".

See also "--ignore-attributes" and "Attributes".


type: string; default: wait_timeout=10000

Set these MySQL variables.  Immediately after connecting to MySQL, this string will be appended to SET and executed.


type: int; default: 1024

Shorten long statements in reports.

Shortens long statements, replacing the omitted portion with a /*... omitted ...*/ comment.  This applies only to the output in reports, not to information stored for "--review" or other places.  It prevents a large statement from causing difficulty in a report.  The argument is the preferred length of the shortened statement.  Not all statements can be shortened, but very large INSERT and similar statements often can; and so can IN() lists, although only the first such list in the statement will be shortened.

If it shortens something beyond recognition, you can find the original statement in the log, at the offset shown in the report header (see "Output").


type: Hash

Show all values for these attributes.

By default mk-query-digest only shows as many of an attribute's value that fit on a single line.  This option allows you to specify attributes for which all values will be shown (line width is ignored).  This only works for attributes with string values like user, host, db, etc.  Multiple attributes can be specified, comma-separated.


type: string

Parse only queries newer than this value (parse queries since this date).

This option allows you to ignore queries older than a certain value and parse only those queries which are more recent than the value.  The value can be several types:

  * Simple time value N with optional suffix: N[shmd], where
    s=seconds, h=hours, m=minutes, d=days (default s if no suffix
    given); this is like saying "since N[shmd] ago"
  * Full date with optional hours:minutes:seconds:
  * Short, MySQL-style date:
  * Any time expression evaluated by MySQL:

If you give a MySQL time expression, then you must also specify a DSN so that mk-query-digest can connect to MySQL to evaluate the expression.  If you specify "--execute", "--explain", "--processlist", "--review" or "--review-history", then one of these DSNs will be used automatically. Otherwise, you must specify an "--aux-dsn" or mk-query-digest will die saying that the value is invalid.

The MySQL time expression is wrapped inside a query like "SELECT UNIX_TIMESTAMP(<expression>)", so be sure that the expression is valid inside this query.  For example, do not use UNIX_TIMESTAMP() because UNIX_TIMESTAMP(UNIX_TIMESTAMP()) returns 0.

Events are assumed to be in chronological--older events at the beginning of the log and newer events at the end of the log.  "--since" is strict: it ignores all queries until one is found that is new enough.  Therefore, if the query events are not consistently timestamped, some may be ignored which are actually new enough.

See also "--until".


short form: -S; type: string

Socket file to use for connection.


Print statistics about internal counters.  This option is mostly for development and debugging.  The statistics report is printed for each iteration after all other reports, even if no events are processed or --no-report is specified.  The statistics report looks like:

   # No events processed.

   # Statistic                                        Count  %/Events
   # ================================================ ====== ========
   # events_read                                      142030   100.00
   # events_parsed                                     50430    35.51
   # events_aggregated                                     0     0.00
   # ignored_midstream_server_response                 18111    12.75
   # no_tcp_data                                       91600    64.49
   # pipeline_restarted_after_MemcachedProtocolParser 142030   100.00
   # pipeline_restarted_after_TcpdumpParser                1     0.00
   # unknown_client_command                                1     0.00
   # unknown_client_data                               32318    22.75

The first column is the internal counter name; the second column is counter's count; and the third column is the count as a percentage of events_read.

In this case, it shows why no events were processed/aggregated: 100% of events were rejected by the MemcachedProtocolParser.  Of those, 35.51% were data packets, but of these 12.75% of ignored mid-stream server response, one was an unknown client command, and 22.75% were unknown client data.  The other 64.49% were TCP control packets (probably most ACKs).

Since mk-query-digest is complex, you will probably need someone familiar with its code to decipher the statistics report.


Print a table access report.

The table access report shows which tables are accessed by all the queries and if the access is a read or write.  The report looks like:

  write `baz`.`tbl`
  read `baz`.`new_tbl`
  write `baz`.`tbl3`
  write `db6`.`tbl6`

If you pipe the output to sort, the read and write tables will be grouped together and sorted alphabetically:

  read `baz`.`new_tbl`
  write `baz`.`tbl`
  write `baz`.`tbl3`
  write `db6`.`tbl6`

type: string

Write the tcpdump data to this file on error.  If mk-query-digest doesn't parse the stream correctly for some reason, the session's packets since the last query event will be written out to create a usable test case.  If this happens, mk-query-digest will not raise an error; it will just discard the session's saved state and permit the tool to continue working.  See "tcpdump" for more information about parsing tcpdump output.


Show a timeline of events.

This option makes mk-query-digest print another kind of report: a timeline of the events.  Each query is still grouped and aggregate into classes according to "--group-by", but then they are printed in chronological order.  The timeline report prints out the timestamp, interval, count and value of each classes.

If all you want is the timeline report, then specify --no-report to suppress the default query analysis report.  Otherwise, the timeline report will be printed at the end before the response-time profile (see "--report-format" and "Output").

For example, this:

  mk-query-digest /path/to/log --group-by distill --timeline

will print something like:

  # ########################################################
  # distill report
  # ########################################################
  # 2009-07-25 11:19:27 1+00:00:01   2 SELECT foo
  # 2009-07-27 11:19:30      00:01   2 SELECT bar
  # 2009-07-27 11:30:00 1+06:30:00   2 SELECT foo

type: Array

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


Parse a binary log file.


Parse a MySQL general log file.  General logs lack a lot of "Attributes", notably Query_time.  The default "--order-by" for general logs changes to Query_time:cnt.


Parse HTTP traffic from tcpdump.


Parse a log file in PostgreSQL format.  The parser will automatically recognize logs sent to syslog and transparently parse the syslog format, too.  The recommended configuration for logging in your postgresql.conf is as follows.

The log_destination setting can be set to either syslog or stderr.  Syslog has the added benefit of not interleaving log messages from several sessions concurrently, which the parser cannot handle, so this might be better than stderr.  CSV-formatted logs are not supported at this time.

The log_min_duration_statement setting should be set to 0 to capture all statements with their durations.  Alternatively, the parser will also recognize and handle various combinations of log_duration and log_statement.

You may enable log_connections and log_disconnections, but this is optional.

It is highly recommended to set your log_line_prefix to the following:

  log_line_prefix = '%m c=%c,u=%u,D=%d '

This lets the parser find timestamps with milliseconds, session IDs, users, and databases from the log.  If these items are missing, you'll simply get less information to analyze.  For compatibility with other log analysis tools such as PQA and pgfouine, various log line prefix formats are supported.  The general format is as follows: a timestamp can be detected and extracted (the syslog timestamp is NOT parsed), and a name=value list of properties can also. Although the suggested format is as shown above, any name=value list will be captured and interpreted by using the first letter of the 'name' part, lowercased, to determine the meaning of the item.  The lowercased first letter is interpreted to mean the same thing as PostgreSQL's built-in %-codes for the log_line_prefix format string.  For example, u means user, so unicorn=fred will be interpreted as user=fred; d means database, so D=john will be interpreted as database=john.  The pgfouine-suggested formatting is user=%u and db=%d, so it should Just Work regardless of which format you choose.  The main thing is to add as much information as possible into the log_line_prefix to permit richer analysis.

Currently, only English locale messages are supported, so if your server's locale is set to something else, the log won't be parsed properly.  (Log messages with "duration:" and "statement:" won't be recognized.)


Parse a log file in any variation of MySQL slow-log format.


Inspect network packets and decode the MySQL client protocol, extracting queries and responses from it.

mk-query-digest does not actually watch the network (i.e. it does NOT "sniff packets").  Instead, it's just parsing the output of tcpdump.  You are responsible for generating this output; mk-query-digest does not do it for you. Then you send this to mk-query-digest as you would any log file: as files on the command line or to STDIN.

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
  mk-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
         > tcp 37
      0x0000:  4508 0059 6eb2 4000 4006 cde2 7f00 0001
      0x0010:  ....

Remember tcpdump has a handy -c option to stop after it captures some number of packets!  That's very useful for testing your tcpdump command.  Note that tcpdump can't capture traffic on a Unix socket.  Read <http://bugs.mysql.com/bug.php?id=31577> if you're confused about this.

Devananda Van Der Veen explained on the MySQL Performance Blog how to capture traffic without dropping packets on busy servers.  Dropped packets cause mk-query-digest to miss the response to a request, then see the response to a later request and assign the wrong execution time to the query.  You can change the filter to something like the following to help capture a subset of the queries.  (See <http://www.mysqlperformanceblog.com/?p=6092> for details.)

  tcpdump -i any -s 65535 -x -n -q -tttt \
     'port 3306 and tcp[1] & 7 == 2 and tcp[3] & 7 == 2'

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,,, 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 MySQL server that is not running on port 3306, see "--watch-server".

Also note that mk-query-digest may fail to report the database for queries when parsing tcpdump output.  The database is discovered only in the initial connect events for a new client or when <USE db> is executed.  If the tcpdump output contains neither of these, then mk-query-digest cannot discover the database.

Server-side prepared statements are supported.  SSL-encrypted traffic cannot be inspected and decoded.


Similar to tcpdump, but the expected input is memcached packets instead of MySQL packets.  For example:

  tcpdump -i any port 11211 -s 65535 -x -nn -q -tttt \
    > memcached.tcp.txt
  mk-query-digest --type memcached memcached.tcp.txt

memcached uses port 11211 by default.


type: string

Parse only queries older than this value (parse queries until this date).

This option allows you to ignore queries newer than a certain value and parse only those queries which are older than the value.  The value can be one of the same types listed for "--since".

Unlike "--since", "--until" is not strict: all queries are parsed until one has a timestamp that is equal to or greater than "--until".  Then all subsequent queries are ignored.


short form: -u; type: string

User for login if not current user.


type: Array

Report the number of variations in these attributes' values.

Variations show how many distinct values an attribute had within a class. The usual value for this option is arg which shows how many distinct queries were in the class.  This can be useful to determine a query's cacheability.

Distinct values are determined by CRC32 checksums of the attributes' values. These checksums are reported in the query report for attributes specified by this option, like:

  # arg crc      109 (1/25%), 144 (1/25%)... 2 more

In that class there were 4 distinct queries.  The checksums of the first two variations are shown, and each one occurred once (or, 25% of the time).

The counts of distinct variations is approximate because only 1,000 variations are saved.  The mod (%) 1000 of the full CRC32 checksum is saved, so some distinct checksums are treated as equal.


Show version and exit.


type: string

This option tells mk-query-digest which server IP address and port (like "") to watch when parsing tcpdump (for "--type" tcpdump and memcached); all other servers are ignored.  If you don't specify it, mk-query-digest watches all servers by looking for any IP address using port 3306 or "mysql".  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.

If you want to watch a mix of servers, some running on standard port 3306 and some running on non-standard ports, you need to create separate tcpdump outputs for the non-standard port servers and then specify this option for each.  At present mk-query-digest cannot auto-detect servers on port 3306 and also be told to watch a server on a non-standard port.


default: yes

Zero out the Rows_XXX properties for administrator command events.


default: yes

Print 0% boolean values in report.

DSN Options

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 maatkit manpage for full details.


You can download Maatkit from Google Code at <http://code.google.com/p/maatkit/>, or you can get any of the tools easily with a command like the following:

   wget http://www.maatkit.org/get/toolname
   wget http://www.maatkit.org/trunk/toolname

Where toolname can be replaced with the name (or fragment of a name) of any of the Maatkit tools.  Once downloaded, they're ready to run; no installation is needed.  The first URL gets the latest released version of the tool, and the second gets the latest trunk code from Subversion.


The environment variable MKDEBUG enables verbose debugging output in all of the Maatkit tools:

   MKDEBUG=1 mk-....

System Requirements

You need Perl 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.maatkit.org/bugs/mk-query-digest>.

Please use Google Code Issues and Groups to report bugs or request support: <http://code.google.com/p/maatkit/>.  You can also join #maatkit on Freenode to discuss Maatkit.

Please include the complete command-line used to reproduce the problem you are seeing, the version of all MySQL servers involved, the complete output of the tool when run with "--version", and if possible, debugging output produced by running with the MKDEBUG=1 environment variable.

Copyright, License and Warranty

This program is copyright 2007-2011 Baron Schwartz. Feedback and improvements are welcome.


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.


Baron Schwartz, Daniel Nichter

About Maatkit

This tool is part of Maatkit, a toolkit for power users of MySQL.  Maatkit was created by Baron Schwartz; Baron and Daniel Nichter are the primary code contributors.  Both are employed by Percona.  Financial support for Maatkit development is primarily provided by Percona and its clients.


This manual page documents Ver 0.9.29 Distrib 7540 $Revision: 7531 $.


2024-01-25 perl v5.38.2 User Contributed Perl Documentation