PT-TABLE-CHECKSUM(1)

NAME
pt-table-checksum - Verify MySQL replication integrity.

SYNOPSIS
Usage: pt-table-checksum [OPTION...] [DSN]

pt-table-checksum performs an online replication consistency check by executing checksum queries on the master, which produces different results on replicas that are inconsistent with the master. The optional DSN specifies the master host. The tool's exit status is nonzero if any differences are found, or if any warnings or errors occur.

The following command will connect to the replication master on localhost, checksum every table, and report the results on every detected replica:

   pt-table-checksum

This tool is focused on finding data differences efficiently. If any data is different, you can resolve the problem with pt-table-sync.

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-table-checksum can add load to the MySQL server, although it has many safeguards to prevent this. It inserts a small amount of data into a table that contains checksum results. It has checks that, if disabled, can potentially cause replication to fail when unsafe replication options are used. In short, it is safe by default, but it permits you to turn off its safety checks.

The tool presumes that schemas and tables are identical on the master and all replicas. Replication will break if, for example, a replica does not have a schema that exists on the master (and that schema is checksummed), or if the structure of a table on a replica is different than on the master.

At the time of this release, we know of no bugs that could cause 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-table-checksum <http://www.percona.com/bugs/pt-table-checksum>.

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

DESCRIPTION
pt-table-checksum is designed to do the right thing by default in almost every case. When in doubt, use "--explain" to see how the tool will checksum a table. The following is a high-level overview of how the tool functions.

In contrast to older versions of pt-table-checksum, this tool is focused on a single purpose, and does not have a lot of complexity or support many different checksumming techniques. It executes checksum queries on only one server, and these flow through replication to re-execute on replicas. If you need the older behavior, you can use Percona Toolkit version 1.0.

pt-table-checksum connects to the server you specify, and finds databases and tables that match the filters you specify (if any). It works one table at a time, so it does not accumulate large amounts of memory or do a lot of work before beginning to checksum. This makes it usable on very large servers. We have used it on servers with hundreds of thousands of databases and tables, and trillions of rows. No matter how large the server is, pt-table-checksum works equally well.

One reason it can work on very large tables is that it divides each table into chunks of rows, and checksums each chunk with a single REPLACE..SELECT query. It varies the chunk size to make the checksum queries run in the desired amount of time. The goal of chunking the tables, instead of doing each table with a single big query, is to ensure that checksums are unintrusive and don't cause too much replication lag or load on the server. That's why the target time for each chunk is 0.5 seconds by default.

The tool keeps track of how quickly the server is able to execute the queries, and adjusts the chunks as it learns more about the server's performance. It uses an exponentially decaying weighted average to keep the chunk size stable, yet remain responsive if the server's performance changes during checksumming for any reason. This means that the tool will quickly throttle itself if your server becomes heavily loaded during a traffic spike or a background task, for example.

Chunking is accomplished by a technique that we used to call "nibbling" in other tools in Percona Toolkit. It is the same technique used for pt-archiver, for example. The legacy chunking algorithms used in older versions of pt-table-checksum are removed, because they did not result in predictably sized chunks, and didn't work well on many tables. All that is required to divide a table into chunks is an index of some sort (preferably a primary key or unique index). If there is no index, and the table contains a suitably small number of rows, the tool will checksum the table in a single chunk.

pt-table-checksum has many other safeguards to ensure that it does not interfere with any server's operation, including replicas. To accomplish this, pt-table-checksum detects replicas and connects to them automatically. (If this fails, you can give it a hint with the "--recursion-method" option.)

The tool monitors replicas continually. If any replica falls too far behind in replication, pt-table-checksum pauses to allow it to catch up. If any replica has an error, or replication stops, pt-table-checksum pauses and waits. In addition, pt-table-checksum looks for common causes of problems, such as replication filters, and refuses to operate unless you force it to. Replication filters are dangerous, because the queries that pt-table-checksum executes could potentially conflict with them and cause replication to fail.

pt-table-checksum verifies that chunks are not too large to checksum safely. It performs an EXPLAIN query on each chunk, and skips chunks that might be larger than the desired number of rows. You can configure the sensitivity of this safeguard with the "--chunk-size-limit" option. If a table will be checksummed in a single chunk because it has a small number of rows, then pt-table-checksum additionally verifies that the table isn't oversized on replicas. This avoids the following scenario: a table is empty on the master but is very large on a replica, and is checksummed in a single large query, which causes a very long delay in replication.

There are several other safeguards. For example, pt-table-checksum sets its session-level innodb_lock_wait_timeout to 1 second, so that if there is a lock wait, it will be the victim instead of causing other queries to time out. Another safeguard checks the load on the database server, and pauses if the load is too high. There is no single right answer for how to do this, but by default pt-table-checksum will pause if there are more than 25 concurrently executing queries. You should probably set a sane value for your server with the "--max-load" option.

Checksumming usually is a low-priority task that should yield to other work on the server. However, a tool that must be restarted constantly is difficult to use. Thus, pt-table-checksum is very resilient to errors. For example, if the database administrator needs to kill pt-table-checksum's queries for any reason, that is not a fatal error. Users often run pt-kill to kill any long-running checksum queries. The tool will retry a killed query once, and if it fails again, it will move on to the next chunk of that table. The same behavior applies if there is a lock wait timeout. The tool will print a warning if such an error happens, but only once per table. If the connection to any server fails, pt-table-checksum will attempt to reconnect and continue working.

If pt-table-checksum encounters a condition that causes it to stop completely, it is easy to resume it with the "--resume" option. It will begin from the last chunk of the last table that it processed. You can also safely stop the tool with CTRL-C. It will finish the chunk it is currently processing, and then exit. You can resume it as usual afterwards.

After pt-table-checksum finishes checksumming all of the chunks in a table, it pauses and waits for all detected replicas to finish executing the checksum queries. Once that is finished, it checks all of the replicas to see if they have the same data as the master, and then prints a line of output with the results. You can see a sample of its output later in this documentation.

The tool prints progress indicators during time-consuming operations. It prints a progress indicator as each table is checksummed. The progress is computed by the estimated number of rows in the table. It will also print a progress report when it pauses to wait for replication to catch up, and when it is waiting to check replicas for differences from the master. You can make the output less verbose with the "--quiet" option.

If you wish, you can query the checksum tables manually to get a report of which tables and chunks have differences from the master. The following query will report every database and table with differences, along with a summary of the number of chunks and rows possibly affected:

  SELECT db, tbl, SUM(this_cnt) AS total_rows, COUNT(*) AS chunks
  FROM percona.checksums
  WHERE (
   master_cnt <> this_cnt
   OR master_crc <> this_crc
   OR ISNULL(master_crc) <> ISNULL(this_crc))
  GROUP BY db, tbl;

The table referenced in that query is the checksum table, where the checksums are stored. Each row in the table contains the checksum of one chunk of data from some table in the server.

Version 2.0 of pt-table-checksum is not backwards compatible with pt-table-sync version 1.0. In some cases this is not a serious problem. Adding a "boundaries" column to the table, and then updating it with a manually generated WHERE clause, may suffice to let pt-table-sync version 1.0 interoperate with pt-table-checksum version 2.0. Assuming an integer primary key named 'id', You can try something like the following:

  ALTER TABLE checksums ADD boundaries VARCHAR(500);
  UPDATE checksums
   SET boundaries = COALESCE(CONCAT('id BETWEEN ', lower_boundary,
      ' AND ', upper_boundary), '1=1');

OUTPUT
The tool prints tabular results, one line per table:

              TS ERRORS  DIFFS  ROWS  CHUNKS SKIPPED    TIME TABLE
  10-20T08:36:50      0      0   200       1       0   0.005 db1.tbl1
  10-20T08:36:50      0      0   603       7       0   0.035 db1.tbl2
  10-20T08:36:50      0      0    16       1       0   0.003 db2.tbl3
  10-20T08:36:50      0      0   600       6       0   0.024 db2.tbl4

Errors, warnings, and progress reports are printed to standard error. See also "--quiet".

Each table's results are printed when the tool finishes checksumming the table. The columns are as follows:

TS  The timestamp (without the year) when the tool finished checksumming the table.

ERRORS
    The number of errors and warnings that occurred while checksumming the table. Errors and warnings are printed to standard error while the table is in progress.

DIFFS
    The number of chunks that differ from the master on one or more replicas. If "--no-replicate-check" is specified, this column will always have zeros. If "--replicate-check-only" is specified, then only tables with differences are printed.

ROWS
    The number of rows selected and checksummed from the table. It might be different from the number of rows in the table if you use the --where option.

CHUNKS
    The number of chunks into which the table was divided.

SKIPPED
    The number of chunks that were skipped due to errors or warnings, or because they were oversized.

TIME
    The time elapsed while checksumming the table.

TABLE
    The database and table that was checksummed.

If "--replicate-check-only" is specified, only checksum differences on detected replicas are printed. The output is different: one paragraph per replica, one checksum difference per line, and values are separted by spaces:

  Differences on h=127.0.0.1,P=12346
  TABLE CHUNK CNT_DIFF CRC_DIFF CHUNK_INDEX LOWER_BOUNDARY UPPER_BOUNDARY
  db1.tbl1 1 0 1 PRIMARY 1 100
  db1.tbl1 6 0 1 PRIMARY 501 600

  Differences on h=127.0.0.1,P=12347
  TABLE CHUNK CNT_DIFF CRC_DIFF CHUNK_INDEX LOWER_BOUNDARY UPPER_BOUNDARY
  db1.tbl1 1 0 1 PRIMARY 1 100
  db2.tbl2 9 5 0 PRIMARY 101 200

The first line of a paragraph indicates the replica with differences. In this example there are two: h=127.0.0.1,P=12346 and h=127.0.0.1,P=12347. The columns are as follows:

TABLE
    The database and table that differs from the master.

CHUNK
    The chunk number of the table that differs from the master.

CNT_DIFF
    The number of chunk rows on the replica minus the number of chunk rows on the master.

CRC_DIFF
    1 if the CRC of the chunk on the replica is different than the CRC of the chunk on the master, else 0.

CHUNK_INDEX
    The index used to chunk the table.

LOWER_BOUNDARY
    The index values that define the lower boundary of the chunk.

UPPER_BOUNDARY
    The index values that define the upper boundary of the chunk.

EXIT STATUS
A non-zero exit status indicates errors, warnings, or checksum differences.

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

--ask-pass
    group: Connection

    Prompt for a password when connecting to MySQL.

--check-interval
    type: time; default: 1; group: Throttle

    Sleep time between checks for "--max-lag".

--[no]check-plan
    default: yes

    Check query execution plans for safety. By default, this option causes pt-table-checksum to run EXPLAIN before running queries that are meant to access a small amount of data, but which could access many rows if MySQL chooses a bad execution plan. These include the queries to determine chunk boundaries and the chunk queries themselves. If it appears that MySQL will use a bad query execution plan, the tool will skip the chunk of the table.

    The tool uses several heuristics to determine whether an execution plan is bad. The first is whether EXPLAIN reports that MySQL intends to use the desired index to access the rows. If MySQL chooses a different index, the tool considers the query unsafe.

    The tool also checks how much of the index MySQL reports that it will use for the query. The EXPLAIN output shows this in the key_len column. The tool remembers the largest key_len seen, and skips chunks where MySQL reports that it will use a smaller prefix of the index. This heuristic can be understood as skipping chunks that have a worse execution plan than other chunks.

    The tool prints a warning the first time a chunk is skipped due to a bad execution plan in each table. Subsequent chunks are skipped silently, although you can see the count of skipped chunks in the SKIPPED column in the tool's output.

    This option adds some setup work to each table and chunk. Although the work is not intrusive for MySQL, it results in more round-trips to the server, which consumes time. Making chunks too small will cause the overhead to become relatively larger. It is therefore recommended that you not make chunks too small, because the tool may take a very long time to complete if you do.

--[no]check-replication-filters
    default: yes; group: Safety

    Do not checksum if any replication filters are set on any replicas. The tool looks for server options that filter replication, such as binlog_ignore_db and replicate_do_db. If it finds any such filters, it aborts with an error.

    If the replicas are configured with any filtering options, you should be careful not to checksum any databases or tables that exist on the master and not the replicas. Changes to such tables might normally be skipped on the replicas because of the filtering options, but the checksum queries modify the contents of the table that stores the checksums, not the tables whose data you are checksumming. Therefore, these queries will be executed on the replica, and if the table or database you're checksumming does not exist, the queries will cause replication to fail. For more information on replication rules, see http://dev.mysql.com/doc/en/replication-rules.html <http://dev.mysql.com/doc/en/replication-rules.html>.

    Replication filtering makes it impossible to be sure that the checksum queries won't break replication (or simply fail to replicate). If you are sure that it's OK to run the checksum queries, you can negate this option to disable the checks. See also "--replicate-database".

--check-slave-lag
    type: string; group: Throttle

    Pause checksumming until this replica's lag is less than "--max-lag". The value is a DSN that inherits properties from the master host and the connection options ("--port", "--user", etc.). This option overrides the normal behavior of finding and continually monitoring replication lag on ALL connected replicas. If you don't want to monitor ALL replicas, but you want more than just one replica to be monitored, then use the DSN option to the "--recursion-method" option instead of this option.

--chunk-index
    type: string

    Prefer this index for chunking tables. By default, pt-table-checksum chooses the most appropriate index for chunking. This option lets you specify the index that you prefer. If the index doesn't exist, then pt-table-checksum will fall back to its default behavior of choosing an index. pt-table-checksum adds the index to the checksum SQL statements in a "FORCE INDEX" clause. Be careful when using this option; a poor choice of index could cause bad performance. This is probably best to use when you are checksumming only a single table, not an entire server.

--chunk-index-columns
    type: int

    Use only this many left-most columns of a "--chunk-index". This works only for compound indexes, and is useful in cases where a bug in the MySQL query optimizer (planner) causes it to scan a large range of rows instead of using the index to locate starting and ending points precisely. This problem sometimes occurs on indexes with many columns, such as 4 or more. If this happens, the tool might print a warning related to the "--[no]check-plan" option. Instructing the tool to use only the first N columns of the index is a workaround for the bug in some cases.

--chunk-size
    type: size; default: 1000

    Number of rows to select for each checksum query. Allowable suffixes are k, M, G. You should not use this option in most cases; prefer "--chunk-time" instead.

    This option can override the default behavior, which is to adjust chunk size dynamically to try to make chunks run in exactly "--chunk-time" seconds. When this option isn't set explicitly, its default value is used as a starting point, but after that, the tool ignores this option's value. If you set this option explicitly, however, then it disables the dynamic adjustment behavior and tries to make all chunks exactly the specified number of rows.

    There is a subtlety: if the chunk index is not unique, then it's possible that chunks will be larger than desired. For example, if a table is chunked by an index that contains 10,000 of a given value, there is no way to write a WHERE clause that matches only 1,000 of the values, and that chunk will be at least 10,000 rows large. Such a chunk will probably be skipped because of "--chunk-size-limit".

    Selecting a small chunk size will cause the tool to become much slower, in part because of the setup work required for "--[no]check-plan".

--chunk-size-limit
    type: float; default: 2.0; group: Safety

    Do not checksum chunks this much larger than the desired chunk size.

    When a table has no unique indexes, chunk sizes can be inaccurate. This option specifies a maximum tolerable limit to the inaccuracy. The tool uses <EXPLAIN> to estimate how many rows are in the chunk. If that estimate exceeds the desired chunk size times the limit (twice as large, by default), then the tool skips the chunk.

    The minimum value for this option is 1, which means that no chunk can be larger than "--chunk-size". You probably don't want to specify 1, because rows reported by EXPLAIN are estimates, which can be different from the real number of rows in the chunk. If the tool skips too many chunks because they are oversized, you might want to specify a value larger than the default of 2.

    You can disable oversized chunk checking by specifying a value of 0.

--chunk-time
    type: float; default: 0.5

    Adjust the chunk size dynamically so each checksum query takes this long to execute.

    The tool tracks the checksum rate (rows per second) for all tables and each table individually. It uses these rates to adjust the chunk size after each checksum query, so that the next checksum query takes this amount of time (in seconds) to execute.

    The algorithm is as follows: at the beginning of each table, the chunk size is initialized from the overall average rows per second since the tool began working, or the value of "--chunk-size" if the tool hasn't started working yet. For each subsequent chunk of a table, the tool adjusts the chunk size to try to make queries run in the desired amount of time. It keeps an exponentially decaying moving average of queries per second, so that if the server's performance changes due to changes in server load, the tool adapts quickly. This allows the tool to achieve predictably timed queries for each table, and for the server overall.

    If this option is set to zero, the chunk size doesn't auto-adjust, so query checksum times will vary, but query checksum sizes will not. Another way to do the same thing is to specify a value for "--chunk-size" explicitly, instead of leaving it at the default.

--columns
    short form: -c; type: array; group: Filter

    Checksum only this comma-separated list of columns.

--config
    type: Array; group: Config

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

--[no]create-replicate-table
    default: yes

    Create the "--replicate" database and table if they do not exist. The structure of the replicate table is the same as the suggested table mentioned in "--replicate".

--databases
    short form: -d; type: hash; group: Filter

    Only checksum this comma-separated list of databases.

--databases-regex
    type: string; group: Filter

    Only checksum databases whose names match this Perl regex.

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

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

--[no]empty-replicate-table
    default: yes

    Delete previous checksums for each table before checksumming the table. This option does not truncate the entire table, it only deletes rows (checksums) for each table just before checksumming the table. Therefore, if checksumming stops prematurely and there was preexisting data, there will still be rows for tables that were not checksummed before the tool was stopped.

    If you're resuming from a previous checksum run, then the checksum records for the table from which the tool resumes won't be emptied.

--engines
    short form: -e; type: hash; group: Filter

    Only checksum tables which use these storage engines.

--explain
    cumulative: yes; default: 0; group: Output

    Show, but do not execute, checksum queries (disables "--[no]empty-replicate-table"). If specified twice, the tool actually iterates through the chunking algorithm, printing the upper and lower boundary values for each chunk, but not executing the checksum queries.

--float-precision
    type: int

    Precision for FLOAT and DOUBLE number-to-string conversion. Causes FLOAT and DOUBLE values to be rounded to the specified number of digits after the decimal point, with the ROUND() function in MySQL. This can help avoid checksum mismatches due to different floating-point representations of the same values on different MySQL versions and hardware. The default is no rounding; the values are converted to strings by the CONCAT() function, and MySQL chooses the string representation. If you specify a value of 2, for example, then the values 1.008 and 1.009 will be rounded to 1.01, and will checksum as equal.

--function
    type: string

    Hash function for checksums (FNV1A_64, MURMUR_HASH, SHA1, MD5, CRC32, etc).

    The default is to use CRC32(), but MD5() and SHA1() also work, and you can use your own function, such as a compiled UDF, if you wish. The function you specify is run in SQL, not in Perl, so it must be available to MySQL.

    MySQL doesn't have good built-in hash functions that are fast. CRC32() is too prone to hash collisions, and MD5() and SHA1() are very CPU-intensive. The FNV1A_64() UDF that is distributed with Percona Server is a faster alternative. It is very simple to compile and install; look at the header in the source code for instructions. If it is installed, it is preferred over MD5(). You can also use the MURMUR_HASH() function if you compile and install that as a UDF; the source is also distributed with Percona Server, and it might be better than FNV1A_64().

--help
    group: Help

    Show help and exit.

--host
    short form: -h; type: string; default: localhost; group: Connection

    Host to connect to.

--ignore-columns
    type: Hash; group: Filter

    Ignore this comma-separated list of columns when calculating the checksum.

--ignore-databases
    type: Hash; group: Filter

    Ignore this comma-separated list of databases.

--ignore-databases-regex
    type: string; group: Filter

    Ignore databases whose names match this Perl regex.

--ignore-engines
    type: Hash; default: FEDERATED,MRG_MyISAM; group: Filter

    Ignore this comma-separated list of storage engines.

--ignore-tables
    type: Hash; group: Filter

    Ignore this comma-separated list of tables. Table names may be qualified with the database name. The "--replicate" table is always automatically ignored.

--ignore-tables-regex
    type: string; group: Filter

    Ignore tables whose names match the Perl regex.

--lock-wait-timeout
    type: int; default: 1

    Set the session value of "innodb_lock_wait_timeout" on the master host. This option helps guard against long lock waits if the checksum queries become slow for some reason. Setting this option dynamically requires the InnoDB plugin, so this works only on newer InnoDB and MySQL versions. If setting the value fails and the current server value is greater than the specified value, then a warning is printed; else, if the current server value is less than or equal to the specified value, no warning is printed.

--max-lag
    type: time; default: 1s; group: Throttle

    Pause checksumming until all replicas' lag is less than this value. After each checksum query (each chunk), pt-table-checksum looks at the replication lag of all replicas to which it connects, using Seconds_Behind_Master. If any replica is lagging more than the value of this option, then pt-table-checksum will sleep for "--check-interval" seconds, then check all replicas again. If you specify "--check-slave-lag", then the tool only examines that server for lag, not all servers. If you want to control exactly which servers the tool monitors, use the DSN value to "--recursion-method".

    The tool waits forever for replicas to stop lagging. If any replica is stopped, the tool waits forever until the replica is started. Checksumming continues once all replicas are running and not lagging too much.

    The tool prints progress reports while waiting. If a replica is stopped, it prints a progress report immediately, then again at every progress report interval.

--max-load
    type: Array; default: Threads_running=25; group: Throttle

    Examine SHOW GLOBAL STATUS after every chunk, and pause if any status variables are higher than the threshold. The option accepts a comma-separated list of MySQL status variables to check for a threshold. An optional "=MAX_VALUE" (or ":MAX_VALUE") can follow each variable. If not given, the tool determines a threshold by examining the current value and increasing it by 20%.

    For example, if you want the tool to pause when Threads_connected gets too high, you can specify "Threads_connected", and the tool will check the current value when it starts working and add 20% to that value. If the current value is 100, then the tool will pause when Threads_connected exceeds 120, and resume working when it is below 120 again. If you want to specify an explicit threshold, such as 110, you can use either "Threads_connected:110" or "Threads_connected=110".

    The purpose of this option is to prevent the tool from adding too much load to the server. If the checksum queries are intrusive, or if they cause lock waits, then other queries on the server will tend to block and queue. This will typically cause Threads_running to increase, and the tool can detect that by running SHOW GLOBAL STATUS immediately after each checksum query finishes. If you specify a threshold for this variable, then you can instruct the tool to wait until queries are running normally again. This will not prevent queueing, however; it will only give the server a chance to recover from the queueing. If you notice queueing, it is best to decrease the chunk time.

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

    Password to use when connecting.

--pid
    type: string

    Create the given PID file. The file contains the process ID of the script. The PID file is removed when the script exits. Before starting, the script checks if the PID file already exists. If it does not, then the script creates and writes its own PID to it. If it does, then the script checks the following: if the file contains a PID and a process is running with that PID, then the script dies; or, if there is no process running with that PID, then the script overwrites the file with its own PID and starts; else, if the file contains no PID, then the script dies.

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

    Port number to use for connection.

--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. The tool prints progress reports for a variety of time-consuming operations, including waiting for replicas to catch up if they become lagged.

--quiet
    short form: -q; cumulative: yes; default: 0

    Print only the most important information (disables "--progress"). Specifying this option once causes the tool to print only errors, warnings, and tables that have checksum differences.

    Specifying this option twice causes the tool to print only errors. In this case, you can use the tool's exit status to determine if there were any warnings or checksum differences.

--recurse
    type: int

    Number of levels to recurse in the hierarchy when discovering replicas. Default is infinite. See also "--recursion-method".

--recursion-method
    type: string

    Preferred recursion method for discovering replicas. Possible methods are:

      METHOD       USES
      ===========  ==================
      processlist  SHOW PROCESSLIST
      hosts        SHOW SLAVE HOSTS
      dsn=DSN      DSNs from a table
      none         Do not find slaves

    The processlist method is the default, because SHOW SLAVE HOSTS is not reliable. However, the hosts method can work better if the server uses a non-standard port (not 3306). The tool usually does the right thing and finds all replicas, but you may give a preferred method and it will be used first.

    The hosts method requires replicas to be configured with report_host, report_port, etc.

    The dsn method is special: it specifies a table from which other DSN strings are read. The specified DSN must specify a D and t, or a database-qualified t. The DSN table should have the following structure:

      CREATE TABLE `dsns` (
        `id` int(11) NOT NULL AUTO_INCREMENT,
        `parent_id` int(11) DEFAULT NULL,
        `dsn` varchar(255) NOT NULL,
        PRIMARY KEY (`id`)
      );

    To make the tool monitor only the hosts 10.10.1.16 and 10.10.1.17 for replication lag and checksum differences, insert the values "h=10.10.1.16" and "h=10.10.1.17" into the table. Currently, the DSNs are ordered by id, but id and parent_id are otherwise ignored.

--replicate
    type: string; default: percona.checksums

    Write checksum results to this table. The replicate table must have this structure (MAGIC_create_replicate):

      CREATE TABLE checksums (
         db             char(64)     NOT NULL,
         tbl            char(64)     NOT NULL,
         chunk          int          NOT NULL,
         chunk_time     float            NULL,
         chunk_index    varchar(200)     NULL,
         lower_boundary text             NULL,
         upper_boundary text             NULL,
         this_crc       char(40)     NOT NULL,
         this_cnt       int          NOT NULL,
         master_crc     char(40)         NULL,
         master_cnt     int              NULL,
         ts             timestamp    NOT NULL,
         PRIMARY KEY (db, tbl, chunk),
         INDEX ts_db_tbl (ts, db, tbl)
      ) ENGINE=InnoDB;

    By default, "--[no]create-replicate-table" is true, so the database and the table specified by this option are created automatically if they do not exist.

    Be sure to choose an appropriate storage engine for the replicate table. If you are checksumming InnoDB tables, and you use MyISAM for this table, a deadlock will break replication, because the mixture of transactional and non-transactional tables in the checksum statements will cause it to be written to the binlog even though it had an error. It will then replay without a deadlock on the replicas, and break replication with "different error on master and slave." This is not a problem with pt-table-checksum; it's a problem with MySQL replication, and you can read more about it in the MySQL manual.

    The replicate table is never checksummed (the tool automatically adds this table to "--ignore-tables").

--[no]replicate-check
    default: yes

    Check replicas for data differences after finishing each table. The tool finds differences by executing a simple SELECT statement on all detected replicas. The query compares the replica's checksum results to the master's checksum results. It reports differences in the DIFFS column of the output.

--replicate-check-only
    Check replicas for consistency without executing checksum queries. This option is used only with "--[no]replicate-check". If specified, pt-table-checksum doesn't checksum any tables. It checks replicas for differences found by previous checksumming, and then exits. It might be useful if you run pt-table-checksum quietly in a cron job, for example, and later want a report on the results of the cron job, perhaps to implement a Nagios check.

--replicate-database
    type: string

    USE only this database. By default, pt-table-checksum executes USE to select the database that contains the table it's currently working on. This is is a best effort to avoid problems with replication filters such as binlog_ignore_db and replicate_ignore_db. However, replication filters can create a situation where there simply is no one right way to do things. Some statements might not be replicated, and others might cause replication to fail. In such cases, you can use this option to specify a default database that pt-table-checksum selects with USE, and never changes. See also "--[no]check-replication-filters".

--resume
    Resume checksumming from the last completed chunk (disables "--[no]empty-replicate-table"). If the tool stops before it checksums all tables, this option makes checksumming resume from the last chunk of the last table that it finished.

--retries
    type: int; default: 2

    Retry a chunk this many times when there is a nonfatal error. Nonfatal errors are problems such as a lock wait timeout or the query being killed.

--separator
    type: string; default: #

    The separator character used for CONCAT_WS(). This character is used to join the values of columns when checksumming.

--set-vars
    type: string; default: wait_timeout=10000; group: Connection

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

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

    Socket file to use for connection.

--tables
    short form: -t; type: hash; group: Filter

    Checksum only this comma-separated list of tables. Table names may be qualified with the database name.

--tables-regex
    type: string; group: Filter

    Checksum only tables whose names match this Perl regex.

--trim
    Add TRIM() to VARCHAR columns (helps when comparing 4.1 to >= 5.0). This is useful when you don't care about the trailing space differences between MySQL versions that vary in their handling of trailing spaces. MySQL 5.0 and later all retain trailing spaces in VARCHAR, while previous versions would remove them. These differences will cause false checksum differences.

--user
    short form: -u; type: string; group: Connection

    User for login if not current user.

--version
    group: Help

    Show version and exit.

--where
    type: string

    Do only rows matching this WHERE clause. You can use this option to limit the checksum to only part of the table. This is particularly useful if you have append-only tables and don't want to constantly re-check all rows; you could run a daily job to just check yesterday's rows, for instance.

    This option is much like the -w option to mysqldump. Do not specify the WHERE keyword. You might need to quote the value. Here is an example:

      pt-table-checksum --where "ts > CURRENT_DATE - INTERVAL 1 DAY"

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 percona-toolkit manpage for full details.

•   A

    dsn: charset; copy: yes

    Default character set.

•   D

    copy: no

    DSN table database.

•   F

    dsn: mysql_read_default_file; copy: no

    Only read default options from the given file

•   h

    dsn: host; copy: yes

    Connect to host.

•   p

    dsn: password; copy: yes

    Password to use when connecting.

•   P

    dsn: port; copy: yes

    Port number to use for connection.

•   S

    dsn: mysql_socket; copy: no

    Socket file to use for connection.

•   t

    copy: no

    DSN table table.

•   u

    dsn: user; copy: yes

    User for login if not current user.

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-table-checksum ... > 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-table-checksum <http://www.percona.com/bugs/pt-table-checksum>.

Please report bugs at https://bugs.launchpad.net/percona-toolkit <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/ <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 and Daniel Nichter

ACKNOWLEDGMENTS
Claus Jeppesen, Francois Saint-Jacques, Giuseppe Maxia, Heikki Tuuri, James Briggs, Martin Friebe, and Sergey Zhuravlev

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.

COPYRIGHT, LICENSE, AND WARRANTY
This program is copyright 2007-2011 Baron Schwartz, 2011-2012 Percona Inc. Feedback and improvements are welcome.

THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2; OR the Perl Artistic License. On UNIX and similar systems, you can issue `man perlgpl' or `man perlartistic' to read these licenses.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.

VERSION
pt-table-checksum 2.1.2