mysql 同步工具 mk-table-sync

google和javaeye都很牛叉哈！

 

<!-- INDEX BEGIN -->

• NAME
• SYNOPSIS
• RISKS
• DESCRIPTION
• OUTPUT
• REPLICATION SAFETY
• ALGORITHMS
• BIDIRECTIONAL SYNCING
• EXIT STATUS
• OPTIONS
• DSN OPTIONS
• DOWNLOADING
• ENVIRONMENT
• SYSTEM REQUIREMENTS
• BUGS
• COPYRIGHT, LICENSE AND WARRANTY
• AUTHOR
• ABOUT MAATKIT
• HISTORY AND ACKNOWLEDGEMENTS
• VERSION

---

<!-- INDEX END -->

 

NAME

mk-table-sync - Synchronize MySQL tables efficiently. 同步mysql表

 

---

SYNOPSIS

This tool changes data, so for maximum safety, you should back up your data before you use it. 为安全最好先备份数据

To sync db.tbl1 from host1 to host2:  机器1 to 2

 mk-table-sync --execute u=user,p=pass,h=host1,D=db,t=tbl   host2

Sync all tables in host1 to host2 and host3:

 mk-table-sync --execute host1 host2 host3

Resolve differences mk-table-checksum found on this master's slaves:

 mk-table-sync --execute --replicate test.checksum master1

Make slave1 have the same data as its replication master:

 mk-table-sync --execute --sync-to-master slave1

Ditto, resolving differences mk-table-checksum found:

 mk-table-sync --execute --sync-to-master \
   --replicate test.checksum slave1

Sync server2 in a master-master replication configuration, where server2's copy of db1.tbl1 is known or suspected to be incorrect:

 mk-table-sync --execute --sync-to-master h=server2,D=db1,t=tbl1

Note that in the master-master configuration, the following will NOT do what you want, because it will make changes directly on server2, which will then flow through replication and change server1's data:

 # Don't do this in a master-master setup!
 mk-table-sync --execute h=server1,D=db1,t=tbl1 h=server2

 

---

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.

With great power comes great responsibility! This tool changes data, so it is a good idea to back up your data. It is also very powerful, which means it is very complex, so you should run it with the --dry-run option to see what it will do, until you're familiar with its operation. If you want to see which rows are different, without changing any data, use --print instead of --execute .

Be careful when using mk-table-sync in any master-master setup . Master-master replication is inherently tricky, and it's easy to make mistakes. Yyou need to be sure you're using the tool correctly for master-master replication. See the SYNOPSIS for the overview of the correct usage.

In general, this tool is best suited when your tables have a primary key or unique index . Although it can synchronize data in tables lacking a primary key or unique index, it might be best to sychronize that data by another means.

At the time of this release, there is a potential bug using --lock-and-rename with MySQL 5.1, a bug detecting certain differences, a bug using ROUND() across different platforms, a bug mixing collations, and a bug chunking inside mk-table-checksum boundaries.

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-table-sync .

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

 

---

DESCRIPTION

WARNING this tool is unfinished and could perform slowly. The Chunk algorithm is great when it can be used, and so is Nibble, but otherwise GroupBy is the default choice and it may not perform very well. Please run with --dry-run before subjecting your servers to this tool, and make backups of your data!

This tool is designed to do one-way and bidirectional synchronization of data. It finds differences efficiently with one of several algorithms (see ALGORITHMS ). It makes changes on the destination table(s) so it matches the source.

It does not synchronize table structures, indexes, or any other schema changes . It synchronizes only data.

It can operate through replication by comparing a slave with its master and making changes on the master . These changes will flow through replication and correct any differences found on the slave.

It accepts a list of DSNs (see the --help output) to tell it where and how to connect.

There are many ways to invoke it. The following is the abbreviated logic:

   if DSN has a t part, sync only that table:
      if 1 DSN:
         if --sync-to-master:
            The DSN is a slave.  Connect to its master and sync.
      if more than 1 DSN:
         The first DSN is the source.  Sync each DSN in turn.
   else if --replicate:
      if --sync-to-master:
         The DSN is a slave.  Connect to its master, find records
         of differences, and fix.
      else:
         The DSN is the master.  Find slaves and connect to each,
         find records of differences, and fix.
   else:
      if only 1 DSN and --sync-to-master:
         The DSN is a slave.  Connect to its master, find tables and
         filter with --databases etc, and sync each table to the master.
      else:
         find tables, filtering with --databases etc, and sync each
         DSN to the first.

If you're confused about how it the DSNs are interpreted, use the --explain-hosts option and it will tell you.

 

---

OUTPUT

If you specify the --verbose option, you'll see information about the differences between the tables. There is one row per table. Each server is printed separately. For example,

   # Syncing h=host1,D=test,t=test1
   # DELETE REPLACE INSERT UPDATE ALGORITHM EXIT DATABASE.TABLE
   #      0       0      3      0 Chunk     2    test.test1

Table test.test1 on host1 required 3 INSERT statements to synchronize and it used the Chunk algorithm (see ALGORITHMS ). Because differences were found, its EXIT STATUS was 2.

If you specify the --print option, you'll see the actual SQL statements that the script uses to synchronize the table if --execute is also specified.

If you want to see t he SQL statements that mk-table-sync is using to select chunks, nibbles, rows, etc., then specify --print once and --verbose twice . Be careful though: this can print a lot of SQL statements.

There are cases where no combination of INSERT , UPDATE or DELETE statements can resolve differences without violating some unique key. For example, suppose there's a primary key on column a and a unique key on column b. Then there is no way to sync these two tables with straightforward UPDATE statements:

 +---+---+  +---+---+
 | a | b |  | a | b |
 +---+---+  +---+---+
 | 1 | 2 |  | 1 | 1 |
 | 2 | 1 |  | 2 | 2 |
 +---+---+  +---+---+

The tool rewrites queries to DELETE and REPLACE in this case. This is automatically handled after the first index violation, so you don't have to worry about it.

 

---

REPLICATION SAFETY

Synchronizing a replication master and slave safely is a non-trivial problem, in general. There are all sorts of issues to think about, such as other processes changing data, trying to change data on the slave, whether the destination and source are a master-master pair, and much more.

In general, the safe way to do it is to change the data on the master , and let the changes flow through replication to the slave like any other changes. However, this works only if it's possible to REPLACE into the table on the master. REPLACE works only if there's a unique index on the table (otherwise it just acts like an ordinary INSERT).

If your table has unique keys, you should use the --sync-to-master and/or --replicate options to sync a slave to its master. This will generally do the right thing. When there is no unique key on the table, there is no choice but to change the data on the slave, and mk-table-sync will detect that you're trying to do so. It will complain and die unless you specify --no-check-slave (see --[no]check-slave ).

If you're syncing a table without a primary or unique key on a master-master pair, you must change the data on the destination server. Therefore, you need to specify --no-bin-log for safety (see --[no]bin-log ). If you don't, the changes you make on the destination server will replicate back to the source server and change the data there!

The generally safe thing to do on a master-master pair is to use the --sync-to-master option so you don't change the data on the destination server. You will also need to specify --no-check-slave to keep mk-table-sync from complaining that it is changing data on a slave.

 

---

ALGORITHMS

This tool has a generic data-syncing framework, within which it is possible to use any number of different algorithms to actually find differences . It chooses the best algorithm automatically . While I plan to add more algorithms in the future, the following are implemented now:

Chunk

Finds an index whose first column is numeric (including date and time types), and divides the column's range of values into chunks of approximately --chunk-size rows. Syncs a chunk at a time by checksumming the entire chunk. If the chunk differs on the source and destination, checksums each chunk's rows individually to find the rows that differ .

It is efficient when the column has sufficient cardinality to make the chunks end up about the right size.

The initial per-chunk checksum is quite small and results in minimal network traffic and memory consumption. If a chunk's rows must be examined, only the primary key columns and a checksum are sent over the network, not the entire row. If a row is found to be different, the entire row will be fetched, but not before. 和rsync类似哦，都是先检查checksum是否一致再判断是否需要进一步比较

Nibble

Finds an index and ascends the index in fixed-size nibbles of --chunk-size rows, using a non-backtracking algorithm (see mk-archiver for more on this algorithm). It is very similar to Chunk , but instead of pre-calculating the boundaries of each piece of the table based on index cardinality, it uses LIMIT to define each nibble's upper limit, and the previous nibble's upper limit to define the lower limit.

It works in steps: one query finds the row that will define the next nibble's upper boundary, and the next query checksums the entire nibble. If the nibble differs between the source and destination, it examines the nibble row-by-row, just as Chunk does.

GroupBy

Selects the entire table grouped by all columns, with a COUNT(*) column added. Compares all columns, and if they're the same, compares the COUNT(*) column's value to determine how many rows to insert or delete into the destination. Works on tables with no primary key or unique index .

Stream

Selects the entire table in one big stream and compares all columns. Selects all columns. Much less efficient than the other algorithms, but works when there is no suitable index for them to use .

Future Plans

Possibilities for future algorithms are TempTable (what I originally called bottom-up in earlier versions of this tool), DrillDown (what I originallly called top-down), and GroupByPrefix (similar to how SqlYOG Job Agent works). Each algorithm has strengths and weaknesses. If you'd like to implement your favorite technique for finding differences between two sources of data on possibly different servers, I'm willing to help. The algorithms adhere to a simple interface that makes it pretty easy to write your own.

 

---

BIDIRECTIONAL SYNCING

Bidirectional syncing is a new, experimental feature. To make it work reliably there are a number of strict limitations:

  * only works when syncing one server to other independent servers
  * does not work in any way with replication



  * requires that the table(s) are chunkable with the Chunk algorithm
  * is not N-way, only bidirectional between two servers at a time
  * does not handle DELETE changes

For example, suppose we have three servers: c1, r1, r2. c1 is the central server, a pseudo-master to the other servers (viz. r1 and r2 are not slaves to c1). r1 and r2 are remote servers. Rows in table foo are updated and inserted on all three servers and we want to synchronize all the changes between all the servers. Table foo has columns:

  id    int PRIMARY KEY
  ts    timestamp auto updated
  name  varchar

Auto-increment offsets are used so that new rows from any server do not create conflicting primary key (id) values. In general, newer rows, as determined by the ts column, take precedence when a same but differing row is found during the bidirectional sync. "Same but differing" means that two rows have the same primary key (id) value but different values for some other column, like the name column in this example. Same but differing conflicts are resolved by a "conflict". A conflict compares some column of the competing rows to determine a "winner". The winnning row becomes the source and its values are used to update the other row.

There are subtle differences between three columns used to achieve bidirectional syncing that you should be familiar with: chunk column (--chunk-column ), comparison column(s) (--columns ), and conflict column (--conflict-column ). The chunk column is only used to chunk the table; e.g. "WHERE id >= 5 AND id < 10". Chunks are checksummed and when chunk checksums reveal a difference, the tool selects the rows in that chunk and checksums the --columns for each row. If a column checksum differs, the rows have one or more conflicting column values. In a traditional unidirectional sync, the conflict is a moot point because it can be resolved simply by updating the entire destination row with the source row's values. In a bidirectional sync, however, the --conflict-column (in accordance with other --conflict-* options list below) is compared to determine which row is "correct" or "authoritative"; this row becomes the "source".

To sync all three servers completely, two runs of mk-table-sync are required. The first run syncs c1 and r1, then syncs c1 and r2 including any changes from r1. At this point c1 and r2 are completely in sync, but r1 is missing any changes from r2 because c1 didn't have these changes when it and r1 were synced. So a second run is needed which syncs the servers in the same order, but this time when c1 and r1 are synced r1 gets r2's changes.

The tool does not sync N-ways, only bidirectionally between the first DSN given on the command line and each subsequent DSN in turn. So the tool in this example would be ran twice like:

  mk-table-sync --bidirectional h=c1 h=r1 h=r2

The --bidirectional option enables this feature and causes various sanity checks to be performed. You must specify other options that tell mk-table-sync how to resolve conflicts for same but differing rows. These options are:

  * L<--conflict-column>
  * L<--conflict-comparison>
  * L<--conflict-value>
  * L<--conflict-threshold>
  * L<--conflict-error>  (optional)

Use --print to test this option before --execute . The printed SQL statements will have comments saying on which host the statment would be executed if you used --execute .

Technical side note: the first DSN is always the "left" server and the other DSNs are always the "right" server. Since either server can become the source or destination it's confusing to think of them as "src" and "dst". Therefore, they're generically referred to as left and right. It's easy to remember this because the first DSN is always to the left of the other server DSNs on the command line.

 

---

EXIT STATUS

Exit status is as follows:

   STATUS  MEANING
   ======  =======================================================
   0       Success.
   1       Internal error.
   2       At least one table differed on the destination.
   3       Combination of 1 and 2.

 

---

OPTIONS

Specify at least one of --print , --execute , or --dry-run .dry-run 不执行！

--where and --replicate are mutually exclusive.

--algorithms

type: string; default: Chunk,Nibble,GroupBy,Stream

Algorithm to use when comparing the tables, in order of preference.

For each table, mk-table-sync will check if the table can be synced with the given algorithms in the order that they're given. The first algorithm that can sync the table is used. See ALGORITHMS .

--ask-pass

Prompt for a password when connecting to MySQL.

--bidirectional

Enable bidirectional sync between first and subsequent hosts.

See BIDIRECTIONAL SYNCING for more information.

--[no]bin-log

default: yes

Log to the binary log (SET SQL_LOG_BIN=1 ).

Specifying --no-bin-log will SET SQL_LOG_BIN=0 .

--buffer-in-mysql

Instruct MySQL to buffer queries in its memory.

This option adds the SQL_BUFFER_RESULT option to the comparison queries. This causes MySQL to execute the queries and place them in a temporary table internally before sending the results back to mk-table-sync. The advantage of this strategy is that mk-table-sync can fetch rows as desired without using a lot of memory inside the Perl process, while releasing locks on the MySQL table (to reduce contention with other queries). The disadvantage is that it uses more memory on the MySQL server instead.

You probably want to leave --[no]buffer-to-client enabled too, because buffering into a temp table and then fetching it all into Perl's memory is probably a silly thing to do. This option is most useful for the GroupBy and Stream algorithms, which may fetch a lot of data from the server.

--[no]buffer-to-client

default: yes

Fetch rows one-by-one from MySQL while comparing.

This is disabled by default. If enabled, all rows will be fetched into memory for comparing. This may result in the results "cursor" being held open for a shorter time on the server, but if the tables are large, it could take a long time anyway, and eat all your memory. For most non-trivial data sizes, you want to leave this disabled.

--charset

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.

--[no]check-master

default: yes

With --sync-to-master , try to verify that the detected master is the real master.

--[no]check-privileges

default: yes

Check that user has all necessary privileges on source and destination table.

--[no]check-slave

default: yes

Check whether the destination server is a slave.

If the destination server is a slave, it's generally unsafe to make changes on it. However, sometimes you have to; --replace won't work unless there's a unique index, for example, so you can't make changes on the master in that scenario. By default mk-table-sync will complain if you try to change data on a slave. Specify --no-slave-check to disable this check. Use it at your own risk.

--[no]check-triggers

default: yes

Check that no triggers are defined on the destination table.

Triggers were introduced in MySQL v5.0.2, so for older versions this option has no effect because triggers will not be checked.

--chunk-column

type: string

Chunk the table on this column.

--chunk-index

type: string

Chunk the table using this index.

--chunk-size

type: string; default: 1000

Number of rows or data size per chunk.

The size of each chunk of rows for the Chunk and Nibble algorithms. The size can be either a number of rows, or a data size. Data sizes are specified with a suffix of k=kibibytes, M=mebibytes, G=gibibytes. Data sizes are converted to a number of rows by dividing by the average row length.

--columns

short form: -c; type: array

Compare this comma-separated list of columns.

--config

type: Array

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

--conflict-column

type: string

Compare this column when rows conflict during a --bidirectional sync.

When a same but differing row is found the value of this column from each row is compared according to --conflict-comparison , --conflict-value and --conflict-threshold to determine which row has the correct data and becomes the source. The column can be any type for which there is an appropriate --conflict-comparison (this is almost all types except, for example, blobs).

This option only works with --bidirectional . See BIDIRECTIONAL SYNCING for more information.

--conflict-comparison

type: string

Choose the --conflict-column with this property as the source.

The option affects how the --conflict-column values from the conflicting rows are compared. Possible comparisons are one of these MAGIC_comparisons:

  newest|oldest|greatest|least|equals|matches

  COMPARISON  CHOOSES ROW WITH
  ==========  =========================================================
  newest      Newest temporal L<--conflict-column> value
  oldest      Oldest temporal L<--conflict-column> value
  greatest    Greatest numerical L<--conflict-column> value
  least       Least numerical L<--conflict-column> value
  equals      L<--conflict-column> value equal to L<--conflict-value>
  matches     L<--conflict-column> value matching Perl regex pattern
              L<--conflict-value>

This option only works with --bidirectional . See BIDIRECTIONAL SYNCING for more information.

--conflict-error

type: string; default: warn

How to report unresolvable conflicts and conflict errors

This option changes how the user is notified when a conflict cannot be resolved or causes some kind of error. Possible values are:

  * warn: Print a warning to STDERR about the unresolvable conflict
  * die:  Die, stop syncing, and print a warning to STDERR

This option only works with --bidirectional . See BIDIRECTIONAL SYNCING for more information.

--conflict-threshold

type: string

Amount by which one --conflict-column must exceed the other.

The --conflict-threshold prevents a conflict from being resolved if the absolute difference between the two --conflict-column values is less than this amount. For example, if two --conflict-column have timestamp values "2009-12-01 12:00:00" and "2009-12-01 12:05:00" the difference is 5 minutes. If --conflict-threshold is set to "5m" the conflict will be resolved, but if --conflict-threshold is set to "6m" the conflict will fail to resolve because the difference is not greater than or equal to 6 minutes. In this latter case, --conflict-error will report the failure.

This option only works with --bidirectional . See BIDIRECTIONAL SYNCING for more information.

--conflict-value

type: string

Use this value for certain --conflict-comparison .

This option gives the value for equals and matches --conflict-comparison .

This option only works with --bidirectional . See BIDIRECTIONAL SYNCING for more information.

--databases

short form: -d; type: hash

Sync only this comma-separated list of databases.

A common request is to sync tables from one database with tables from another database on the same or different server. This is not yet possible. --databases will not do it, and you can't do it with the D part of the DSN either because in the absence of a table name it assumes the whole server should be synced and the D part controls only the connection's default database.

--defaults-file

short form: -F; type: string

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

--dry-run

Analyze, decide the sync algorithm to use, print and exit.

Implies --verbose so you can see the results. The results are in the same output format that you'll see from actually running the tool, but there will be zeros for rows affected. This is because the tool actually executes, but stops before it compares any data and just returns zeros. The zeros do not mean there are no changes to be made.

--engines

short form: -e; type: hash

Sync only this comma-separated list of storage engines.

--execute

Execute queries to make the tables have identical data.

This option makes mk-table-sync actually sync table data by executing all the queries that it created to resolve table differences. Therefore, the tables will be changed! And unless you also specify --verbose , the changes will be made silently. If this is not what you want, see --print or --dry-run .

--explain-hosts

Print connection information and exit.

Print out a list of hosts to which mk-table-sync will connect, with all the various connection options, and exit.

--float-precision

type: int

Precision for FLOAT and DOUBLE column comparisons.

If you specify this option, FLOAT and DOUBLE columns will be rounded to the specified number of digits after the decimal point for the checksum. This can avoid mismatches due to different floating-point representations of the same values on different MySQL versions and hardware.

--[no]foreign-key-checks

default: yes

Enable foreign key checks (SET FOREIGN_KEY_CHECKS=1 ).

Specifying --no-foreign-key-checks will SET FOREIGN_KEY_CHECKS=0 .

--function

type: string

Which hash function you'd like to use for checksums.

The default is CRC32 . Other good choices include MD5 and SHA1 . If you have installed the FNV_64 user-defined function, mk-table-sync will detect it and prefer to use it, because it is much faster than the built-ins. You can also use MURMUR_HASH if you've installed that user-defined function. Both of these are distributed with Maatkit. See mk-table-checksum for more information and benchmarks.

--help

Show help and exit.

--[no]hex-blob

default: yes

HEX() BLOB , TEXT and BINARY columns.

When row data from the source is fetched to create queries to sync the data (i.e. the queries seen with --print and exeucted by --execute ), binary columns are wrapped in HEX() so the binary data does not produce an invalid SQL statement. You can disable this option but you probably shouldn't.

--host

short form: -h; type: string

Connect to host.

--ignore-columns

type: Hash

Ignore this comma-separated list of column names in comparisons.

This option causes columns not to be compared. However, if a row is determined to differ between tables, all columns in that row will be synced, regardless. (It is not currently possible to exclude columns from the sync process itself, only from the comparison.)

--ignore-databases

type: Hash

Ignore this comma-separated list of databases.

--ignore-engines

type: Hash; default: FEDERATED,MRG_MyISAM

Ignore this comma-separated list of storage engines.

--ignore-tables

type: Hash

Ignore this comma-separated list of tables.

Table names may be qualified with the database name.

--[no]index-hint

default: yes

Add FORCE/USE INDEX hints to the chunk and row queries.

By default mk-table-sync adds a FORCE/USE INDEX hint to each SQL statement to coerce MySQL into using the index chosen by the sync algorithm or specified by --chunk-index . This is usually a good thing, but in rare cases the index may not be the best for the query so you can suppress the index hint by specifying --no-index-hint and let MySQL choose the index.

This does not affect the queries printed by --print ; it only affects the chunk and row queries that mk-table-sync uses to select and compare rows.

--lock

type: int

Lock tables: 0=none, 1=per sync cycle, 2=per table, or 3=globally.

This uses LOCK TABLES . This can help prevent tables being changed while you're examining them. The possible values are as follows:

  VALUE  MEANING
  =====  =======================================================
  0      Never lock tables.
  1      Lock and unlock one time per sync cycle (as implemented
         by the syncing algorithm).  This is the most granular
         level of locking available.  For example, the Chunk
         algorithm will lock each chunk of C<N> rows, and then
         unlock them if they are the same on the source and the
         destination, before moving on to the next chunk.
  2      Lock and unlock before and after each table.
  3      Lock and unlock once for every server (DSN) synced, with
         C<FLUSH TABLES WITH READ LOCK>.

A replication slave is never locked if --replicate or --sync-to-master is specified, since in theory locking the table on the master should prevent any changes from taking place. (You are not changing data on your slave, right?) If --wait is given, the master (source) is locked and then the tool waits for the slave to catch up to the master before continuing.

If --transaction is specified, LOCK TABLES is not used. Instead, lock and unlock are implemented by beginning and committing transactions. The exception is if --lock is 3.

If --no-transaction is specified, then LOCK TABLES is used for any value of --lock . See --[no]transaction .

--lock-and-rename

Lock the source and destination table, sync, then swap names. This is useful as a less-blocking ALTER TABLE, once the tables are reasonably in sync with each other (which you may choose to accomplish via any number of means, including dump and reload or even something like mk-archiver ). It requires exactly two DSNs and assumes they are on the same server, so it does no waiting for replication or the like. Tables are locked with LOCK TABLES.

--password

short form: -p; type: string

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

Port number to use for connection.

--print

Print queries that will resolve differences.

If you don't trust mk-table-sync , or just want to see what it will do, this is a good way to be safe. These queries are valid SQL and you can run them yourself if you want to sync the tables manually.

--recursion-method

type: string

Preferred recursion method used to find slaves.

Possible methods are:

  METHOD       USES
  ===========  ================
  processlist  SHOW PROCESSLIST
  hosts        SHOW SLAVE HOSTS

The processlist method is preferred because SHOW SLAVE HOSTS is not reliable. However, the hosts method is required if the server uses a non-standard port (not 3306). Usually mk-table-sync does the right thing and finds the slaves, but you may give a preferred method and it will be used first. If it doesn't find any slaves, the other methods will be tried.

--replace

Write all INSERT and UPDATE statements as REPLACE .

This is automatically switched on as needed when there are unique index violations.

--replicate

type: string

Sync tables listed as different in this table.

Specifies that mk-table-sync should examine the specified table to find data that differs. The table is exactly the same as the argument of the same name to mk-table-checksum . That is, it contains records of which tables (and ranges of values) differ between the master and slave.

For each table and range of values that shows differences between the master and slave, mk-table-checksum will sync that table, with the appropriate WHERE clause, to its master.

This automatically sets --wait to 60 and causes changes to be made on the master instead of the slave.

If --sync-to-master is specified, the tool will assume the server you specified is the slave, and connect to the master as usual to sync.

Otherwise, it will try to use SHOW PROCESSLIST to find slaves of the server you specified. If it is unable to find any slaves via SHOW PROCESSLIST , it will inspect SHOW SLAVE HOSTS instead. You must configure each slave's report-host , report-port and other options for this to work right. After finding slaves, it will inspect the specified table on each slave to find data that needs to be synced, and sync it.

The tool examines the master's copy of the table first, assuming that the master is potentially a slave as well. Any table that shows differences there will NOT be synced on the slave(s). For example, suppose your replication is set up as A->B, B->C, B->D. Suppose you use this argument and specify server B. The tool will examine server B's copy of the table. If it looks like server B's data in table test.tbl1 is different from server A's copy, the tool will not sync that table on servers C and D.

--set-vars

type: string; default: wait_timeout=10000

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

--socket

short form: -S; type: string

Socket file to use for connection.

--sync-to-master

Treat the DSN as a slave and sync it to its master.

Treat the server you specified as a slave. Inspect SHOW SLAVE STATUS , connect to the server's master, and treat the master as the source and the slave as the destination. Causes changes to be made on the master. Sets --wait to 60 by default, sets --lock to 1 by default, and disables --[no]transaction by default. See also --replicate , which changes this option's behavior.

--tables

short form: -t; type: hash

Sync only this comma-separated list of tables.

Table names may be qualified with the database name.

--timeout-ok

Keep going if --wait fails.

If you specify --wait and the slave doesn't catch up to the master's position before the wait times out, the default behavior is to abort. This option makes the tool keep going anyway. Warning : if you are trying to get a consistent comparision between the two servers, you probably don't want to keep going after a timeout.

--[no]transaction

Use transactions instead of LOCK TABLES .

The granularity of beginning and committing transactions is controlled by --lock . This is enabled by default, but since --lock is disabled by default, it has no effect.

Most options that enable locking also disable transactions by default, so if you want to use transactional locking (via LOCK IN SHARE MODE and FOR UPDATE , you must specify --transaction explicitly.

If you don't specify --transaction explicitly mk-table-sync will decide on a per-table basis whether to use transactions or table locks. It currently uses transactions on InnoDB tables, and table locks on all others.

If --no-transaction is specified, then mk-table-sync will not use transactions at all (not even for InnoDB tables) and locking is controlled by --lock .

--trim

TRIM() VARCHAR columns in BIT_XOR and ACCUM modes. Helps when comparing MySQL 4.1 to >= 5.0.

This is useful when you don't care about the trailing space differences between MySQL versions which vary in their handling of trailing spaces. MySQL 5.0 and later all retain trailing spaces in VARCHAR , while previous versions would remove them.

--[no]unique-checks

default: yes

Enable unique key checks (SET UNIQUE_CHECKS=1 ).

Specifying --no-unique-checks will SET UNIQUE_CHECKS=0 .

--user

short form: -u; type: string

User for login if not current user.

--verbose

short form: -v; cumulative: yes

Print results of sync operations.

See OUTPUT for more details about the output.

--version

Show version and exit.

--wait

short form: -w; type: time

How long to wait for slaves to catch up to their master.

Make the master wait for the slave to catch up in replication before comparing the tables. The value is the number of seconds to wait before timing out (see also --timeout-ok ). Sets --lock to 1 and --[no]transaction to 0 by default. If you see an error such as the following,

  MASTER_POS_WAIT returned -1

It means the timeout was exceeded and you need to increase it.

The default value of this option is influenced by other options. To see what value is in effect, run with --help .

--where

type: string

WHERE clause to restrict syncing to part of the table.

 

---

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.

• A

  dsn: charset; copy: yes

  Default character set.

• D

  dsn: database; copy: yes

  Database containing the table to be synced.

• F

  dsn: mysql_read_default_file; copy: yes

  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: yes

  Socket file to use for connection.

• t

  copy: yes

  Table to be synced.

• u

  dsn: user; copy: yes

  User for login if not current user.

 

---

DOWNLOADING

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




   or
   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.

 

---

ENVIRONMENT

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

   MKDEBUG=1 mk-....

 

---

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.maatkit.org/bugs/mk-table-sync .

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 2007-2010 Baron Schwartz. 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 MERCHANTIBILITY 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.

 

---

AUTHOR

Baron Schwartz

 

---

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.

 

---

HISTORY AND ACKNOWLEDGEMENTS

My work is based in part on Giuseppe Maxia's work on distributed databases, http://www.sysadminmag.com/articles/2004/0408/ and code derived from that article. There is more explanation, and a link to the code, at http://www.perlmonks.org/ .

Another programmer extended Maxia's work even further. Fabien Coelho changed and generalized Maxia's technique, introducing symmetry and avoiding some problems that might have caused too-frequent checksum collisions. This work grew into pg_comparator, http://www.coelho.net/pg_comparator/ . Coelho also explained the technique further in a paper titled "Remote Comparison of Database Tables" (http://cri.ensmp.fr/classement/doc/A-375.pdf ).

This existing literature mostly addressed how to find the differences between the tables, not how to resolve them once found. I needed a tool that would not only find them efficiently, but would then resolve them. I first began thinking about how to improve the technique further with my article http://tinyurl.com/mysql-data-diff-algorithm , where I discussed a number of problems with the Maxia/Coelho "bottom-up" algorithm. After writing that article, I began to write this tool. I wanted to actually implement their algorithm with some improvements so I was sure I understood it completely. I discovered it is not what I thought it was, and is considerably more complex than it appeared to me at first. Fabien Coelho was kind enough to address some questions over email.

The first versions of this tool implemented a version of the Coelho/Maxia algorithm, which I called "bottom-up", and my own, which I called "top-down." Those algorithms are considerably more complex than the current algorithms and I have removed them from this tool, and may add them back later. The improvements to the bottom-up algorithm are my original work, as is the top-down algorithm. The techniques to actually resolve the differences are also my own work.

Another tool that can synchronize tables is the SQLyog Job Agent from webyog. Thanks to Rohit Nadhani, SJA's author, for the conversations about the general techniques. There is a comparison of mk-table-sync and SJA at http://tinyurl.com/maatkit-vs-sqlyog

Thanks to the following people and organizations for helping in many ways:

The Rimm-Kaufman Group http://www.rimmkaufman.com/ , MySQL AB http://www.mysql.com/ , Blue Ridge InternetWorks http://www.briworks.com/ , Percona http://www.percona.com/ , Fabien Coelho, Giuseppe Maxia and others at MySQL AB, Kristian Koehntopp (MySQL AB), Rohit Nadhani