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About Binary Logs

MySQL implements replication by logging queries into a series of binary log files. The files are written to the server's local file system. Slaves connect to the MySQL instance and request these files starting at a specific file and offset.

MySQL's binary logging has the following drawbacks:

  • It maintains a single binary log for the entire system.
  • Fault tolerance is provided by the underlying filesystem, if at all.
  • Unless sync_binlog is enabled, the binary log can become inconsistent with the database as the result of power loss.
  • Static configuration is read only when the server starts, so changes to /etc/my.cnf require server restart.

ClustrixDB surpasses MySQL's capabilities by providing the following additional features:

  • ClustrixDB can maintain multiple independent binary logs (for example, binlogs per table, per database or for a set of tables and databases).
  • The binary logs are fault-tolerant, with the same guarantees as the rest of the ClustrixDB system.
  • Writes to the binlog are transactional, consistent and durable (full ACID guarantee).
  • Binary logs can be created and dropped online.

To configure a ClustrixDB system with a single binary log, issue the following commands:


To disable binary logging and drop (permanently) an existing binlog:

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When running MySQL database as a slave to a ClustrixDB master, ClustrixDB does not support the variable, "binlog_checksum" which causes the master to write checksums for events written to the binary log.

MySQL 5.7 Replication and GTIDs

Beginning optionally with MySQL 5.6 and required in MySQL 5.7, MySQL produces global transaction identifiers (GTIDs). ClustrixDB does not implement nor support GTIDs. To enable replication between ClustrixDB and a MySQL instance that produces GTIDs, the following settings must be configured, dependent on replication direction.

For ClustrixDB (Master) to MySQL 5.7 (Slave) Replication
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You can ignore any errors regarding server_uuid within the Clustrix logs.

For MySQL 5.7 (Master) to ClustrixDB (Slave) Replication
  • Run ClustrixDB 7.6 or higher. 
  • The MySQL master configuration is inconsequential and does not require special changes.
  • Further information is available at Using ClustrixDB as a Slave.
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ClustrixDB will not pass GTID events to its binlogs. This is similar to the behavior of a MySQL 5.6 slave with gtid_mode set to OFF.

Create Replication User

The user name and password used for replication are stored as plain text within the binlogs. As such, Clustrix recommends establishing a separate account for exclusive use with replication to prevent compromising the security of regularly used accounts.

Follow this sample to create an account that will be used when setting up a slave. You must have privileges to CREATE USER and GRANT to perform this step.

Create Replication User

Creating a Binary Log File

To create a binary log, issue the following command:

CREATE BINLOG Syntax
example

Optional attributes are:

  • LOG: A list of specific tables or databases to log
  • IGNORE: A list of specific tables or databases to ignore
  • FORMAT: Format specifier ("statement" or "row").

By default, this command creates a binary log file for the entire cluster in statement format, which is the most common format in MySQL environments. Alternatively, you can create binlogs that scope a database or a list of tables. For more information, please see the section on Binlog scope.

For most workloads, row-based replication provides better performance than statement-based replication. If you are unsure what is most appropriate for your environment, contact Clustrix Support.

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If a database is set to both LOG and IGNORE, ClustrixDB will IGNORE. This deviates from MySQL, which will log and not ignore.

Setting Binary Logging Options

To configure binary logging options, issue the ALTER BINLOG command. Options for the ALTER BINLOG logfile command are as follows.

Flag

Description

LOG (db1, db2)

Only log updates to databases db1 and db2

IGNORE (db3)

Ignore updates to db3

ADD LOG (db4)

Log updates to db4, in addition to others

ADD IGNORE (db5)

Ignore updates to db5, in addition to others

DROP LOG (db6)

Stop logging to db6

LOG ALL

Log updates to all databases (as opposed to specific databases). Does not reset the "ignore" list.)

DISABLE

Disable logging to this binlog

ENABLE

Enable logging to this binlog

RENAME bar

Rename specified binlog to "bar"

FORMAT='row' or 'statement'

Configure log format (row-based or statement-based)

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Beta support for table scope binlogs is available as part of the v6.0 and v7.0 Releases. For more information, please see the section on Binlog Scope.

Displaying Binary Log Information


If only one binary log exists, you can display its filename, segment number and position by issuing the following command:


If more than one binary log exists, the log configured by the global variable Master_status_binlog is displayed. If Master_status_binlog is unset, an error is returned. This behavior is compatible with behavior of the MySQL mysqldump --Master-data command.

To display status for all binary logs, issue the following command:

To display detailed information about binary logs, issue the following command:

Most of this information is not directly useful, though log size can help you decide whether to trim the log.

Trimming a Binary Log

You can trim a binary log using either of the following methods:

  • TRIM BINLOG command
  • trim-binlog script
Trimming using the TRIM BINLOG Command

Back up your database regularly using the mysqldump --Master-data command, which records the binary log filename at the start of the dump. To keep the size of the binary log under control, use this value to trim prior data after backing up. The precise extent to which you trim is a matter of policy: you can choose to retain a week's history, or you might prefer to minimize disk consumption as much as possible by trimming all but the current file. To minimize the amount of space being used by your binary log, trim according to the Slave that is farthest behind in replication.


To list the files that compose the binary log, issue the following command:

The system lists the files that compose the binary log. For example:


To display current Slave locations, issue the SHOW SLAVE STATUS command, which displays status as follows:


The filename argument is the filename returned by the SHOW MASTER STATUS command. The sequence number (Log_File_Seq) indicates the binary log file currently in use (it's the numeric portion of the file name)To delete old binary data without dropping the entire log, issue the following command (where ###### indicates the sequence number):

For example, if the clx001.000283 file were timestamped at 7:15 PM on September 28, 2016, the following sample would delete all log files before that time.

Trimming Using the binlog-trim Script

You can find the binlog-trim script in /bin/binlog-trim of your system.
Usage
binlog-trim [options]
Options

Option

Description

-h, --help

Show this help message and exit

-H HOST, --host=HOST

Specifies the host

-P PORT, --port=PORT

SQL port, default is mysql port: 3306

-u USER, --user=USER

Username, default is root

-p PASSWD, --passwd=PASSWD

Specifies the password

-n NUM_FILES, --num-files=NUM_FILES

Number of files to trim a time

-d, --dry

Do not perform any actual trims

-k KEEP_DAYS, --days=KEEP_DAYS

Keep this many days of binlogs

-i INTERVAL, --interval=INTERVAL

Seconds between trims

-b BINLOG_NAME, --binlog_name=BINLOG_NAME

Name of binlog to trim; must specify if multiple binlogs exist

-M MAX_RUN_TIME_MINS, --max-run-time-mins=MAX_RUN_TIME_MINS

Maximum time (minutes) script may run

-V, --version

Indicates the version.

 

binlog-trim is generally deployed as a cron job on one of the nodes. An example entry to run once a day at 5:35UTC, with a retention policy of 7 days, trimming no more than 50 files at a time, with a minimum 60 second pause between trims, and operating on the binlog called clustrix-bin:

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The INTERVAL is a minimum wait between trims; there is additional logic in the script to prevent the trims from building up too much cleanup work (the logs will indicate this with 'waiting for bigc to pass trim').

Backing Up Binary Logs

Because ClustrixDB binary logs (binlogs) aren't stored as plain files, they cannot be backed up as MySQL binlogs can. For backup purposes, ClustrixDB provides the repclient utility, which copies binlogs from a ClustrixDB or MySQL system as if it were a replication slave. The repclient utility can be run on any ClustrixDB node.


To copy all of the binlogs off a ClustrixDB cluster, perform the following steps:

  1. To list the most recent binlog, issue the SHOW MASTER STATUS command. The command returns a filename such as "clustrix-bin.001903".
  2. Create a directory in the /clustrix mount on a node and cd to it.
  3. To retrieve all binlog files up to the most recent, issue the following command: 

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By default, the tool outputs decoded binlog messages to stdout. To specify an output file, specify the -dumpbinlog option. If you intend to archive the binlogs, omit -logpos, which can create gaps in the resulting binlog. By default, the utility stays connected to the master. To specify when it is to disconnect, include the -end_logname or -end_logpos option.

Valid options for the repclient command are as follows:

Flag

Description

-addr hostname

Database host (default: 127.0.0.1)

-count n

Number of messages to dump

-dumpbinlog

Dump binlog

-end_logname path

Ending replication log name

-end_logpos offset

Ending replication log position (default: EOF)

-help

List command options

-help-debug

List command options plus debugging output options

-logname path

Starting replication log name

-logpos offset

Starting replication log position (default: 4)

-max-packet-size bytes

Maximum packet size (default: 16777216)

-max-retries n

Maximum retries after an error (default: 3)

-no-decode-rows

Don't decode row values

-pass password

Database password (default: #undef)

-perf

Dump performance statistics

-perf-interval seconds

Dump performance statistics interval (default: 30)

-port port

Database port (default: 3306)

-retry-timeout seconds

Timeout in seconds for retries (default: 10)

-set-variable NAME= VALUE

Set a variable to the given value

-slave-id n

Slave ID (default: 1)

-testconnect

Test database connection and display status

-truncate

Truncate any existing files

-user username

Database username (default: "root")

-verbose

Display debugging messages

Excluding A Session from Binary Logs

To prevent a session's statements from being inserted into any binary log, set sql_log_bin to false by issuing the following command:


This variable inherits the value of the identically-named global variable at the start of each session. To replicate from a ClustrixDB instance, set sql_log_bin to true.

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Be careful using sql_log_bin in production. Improper use can lead to data skew between the master and the slave(s).

Dropping a Binary Log File


To stop logging to the specified binary log and drop it from the system, issue the following command:

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You cannot recover a binary log after dropping it.

Global Variables

The following global and session variables control binary log behavior:

NameDescriptionDefault ValueSession Variable
binlog_checksumAlways NONE. Clustrix masters do not support generating event checksums.NONE  
binlog_commit_table_slicesNumber of slices for binlog commit tables or 0 for system selected 
binlog_formatForce all binlogs to log in this format, unless set to 'DEFAULT'.DEFAULT 

(tick)

binlog_read_checkBinlogs recording a statement must log all tables read by the statement, in addition to tables modified by the statement.true 

(tick)

binlog_rotate_thresholdOnce the current binlog segment surpasses this size in bytes, a new binlog segment will be created. Setting this to 0 tells the system to select an appropriate value 
binlog_row_delete_limitMaximum number of rows each BINLOG_DELETE task trims off each time it is run.5000  
binlog_statement_table_slicesNumber of slices for new binlog statement table segments or 0 for system selected 
binlog_trimTRUE when binlog-trim is running. Do not change.false 

(tick)

binlog_trx_checkEvery statement in a transaction must record to the same set of binlogs.true 

(tick)

gtid_modeAlways OFF. Clustrix masters do not support generating GTID events.OFF  
master_status_binlogBinlog used in SHOW MASTER STATUS when used without specifying a binlog. 

(tick)

mysql_binlog_indexer_interval_trxsInterval (in transactions) between binlog index entries.500 
mysql_binlog_indexer_limit_msMaximum time (ms) we spend indexing binlogs during one pass. Do not change.25000  
mysql_binlog_size_limit_bytesMaximum size in bytes allowed per binlog file. This variable cannot be modified if any binlogs exist.104857600 
mysql_binlog_trx_scan_batchsize 500  
mysql_slave_follow_master_binlog_format false  
rebalancer_rebalance_binlogsAllow the rebalancer to move active binlogs.false  
rebalancer_split_binlogsAllow splitting of binlog statement segments.false  
sync_binlogDummy variable for compatibility. 
task_binlog_delete_interval_msMilliseconds between runs of periodic task "binlog_delete". Specify 0 to disable periodic task.2000  
task_binlog_rotate_interval_msMilliseconds between runs of periodic task "binlog_rotate". Specify 0 to disable periodic task.120000  
task_mysql_binlog_indexer_interval_msMilliseconds between runs of periodic task "mysql_binlog_indexer". Specify 0 to disable periodic task.1000  
task_mysql_binlog_index_scrubber_interval_msMilliseconds between runs of periodic task "mysql_binlog_index_scrubber". Specify 0 to disable periodic task.100000  
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Exercise extreme care when changing these settings. The defaults may not be ideal for your system, but they should be reasonable. The product will not warn you if you configure inadvisable settings.

The following pages describe areas that should be understood when using ClustrixDB as a Replication Master

  1. Online Schema Changes
  2. Replicating User Account Management Statements
  3. Using ClustrixDB with Multiple Slaves

 

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