pt-slave-delayp - Online in the Cloud

PROGRAM:

NAME

pt-slave-delay - Make a MySQL slave server lag behind its master.

SYNOPSIS

Usage: pt-slave-delay [OPTIONS] SLAVE_DSN [MASTER_DSN]

pt-slave-delay starts and stops a slave server as needed to make it lag behind the master.
The SLAVE_DSN and MASTER_DSN use DSN syntax, and values are copied from the SLAVE_DSN to
the MASTER_DSN if omitted.

To hold slavehost one minute behind its master for ten minutes:

pt-slave-delay --delay 1m --interval 15s --run-time 10m slavehost

RISKS

Percona Toolkit is mature, proven in the real world, and well tested, but all database
tools can pose a risk to the system and the database server. Before using this tool,
please:

· Read the tool's documentation

· Review the tool's known "BUGS"

· Test the tool on a non-production server

· Backup your production server and verify the backups

DESCRIPTION

"pt-slave-delay" watches a slave and starts and stops its replication SQL thread as
necessary to hold it at least as far behind the master as you request. In practice, it
will typically cause the slave to lag between "--delay" and "--delay"+"--interval" behind
the master.

It bases the delay on binlog positions in the slave's relay logs by default, so there is
no need to connect to the master. This works well if the IO thread doesn't lag the master
much, which is typical in most replication setups; the IO thread lag is usually
milliseconds on a fast network. If your IO thread's lag is too large for your purposes,
"pt-slave-delay" can also connect to the master for information about binlog positions.

If the slave's I/O thread reports that it is waiting for the SQL thread to free some relay
log space, "pt-slave-delay" will automatically connect to the master to find binary log
positions. If "--ask-pass" and "--daemonize" are given, it is possible that this could
cause it to ask for a password while daemonized. In this case, it exits. Therefore, if
you think your slave might encounter this condition, you should be sure to either specify
"--use-master" explicitly when daemonizing, or don't specify "--ask-pass".

The SLAVE_DSN and optional MASTER_DSN are both DSNs. See "DSN OPTIONS". Missing
MASTER_DSN values are filled in with values from SLAVE_DSN, so you don't need to specify
them in both places. "pt-slave-delay" reads all normal MySQL option files, such as
~/.my.cnf, so you may not need to specify username, password and other common options at
all.

"pt-slave-delay" tries to exit gracefully by trapping signals such as Ctrl-C. You cannot
bypass "--[no]continue" with a trappable signal.

PRIVILEGES

pt-slave-delay requires the following privileges: PROCESS, REPLICATION CLIENT, and SUPER.

OUTPUT

If you specify "--quiet", there is no output. Otherwise, the normal output is a status
message consisting of a timestamp and information about what "pt-slave-delay" is doing:
starting the slave, stopping the slave, or just observing.

OPTIONS

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

--ask-pass
Prompt for a password when connecting to MySQL.

--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.

--config
type: Array

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

--[no]continue
default: yes

Continue replication normally on exit. After exiting, restart the slave's SQL thread
with no UNTIL condition, so it will run as usual and catch up to the master. This is
enabled by default and works even if you terminate "pt-slave-delay" with Control-C.

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

--database
short form: -D; type: string

The database to use for the connection.

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

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

--delay
type: time; default: 1h

How far the slave should lag its master.

--help
Show help and exit.

--host
short form: -h; type: string

Connect to host.

--interval
type: time; default: 1m

How frequently "pt-slave-delay" should check whether the slave needs to be started or
stopped.

--log
type: string

Print all output to this file when daemonized.

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

Password to use when connecting. If password contains commas they must be escaped
with a backslash: "exam\,ple"

--pid
type: string

Create the given PID file. The tool won't start if the PID file already exists and
the PID it contains is different than the current PID. However, if the PID file
exists and the PID it contains is no longer running, the tool will overwrite the PID
file with the current PID. The PID file is removed automatically when the tool exits.

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

Port number to use for connection.

--quiet
short form: -q

Don't print informational messages about operation. See OUTPUT for details.

--run-time
type: time

How long "pt-slave-delay" should run before exiting. The default is to run forever.

--set-vars
type: Array

Set the MySQL variables in this comma-separated list of "variable=value" pairs.

By default, the tool sets:

wait_timeout=10000

Variables specified on the command line override these defaults. For example,
specifying "--set-vars wait_timeout=500" overrides the defaultvalue of 10000.

The tool prints a warning and continues if a variable cannot be set.

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

Socket file to use for connection.

--use-master
Get binlog positions from master, not slave. Don't trust the binlog positions in the
slave's relay log. Connect to the master and get binlog positions instead. If you
specify this option without giving a MASTER_DSN on the command line, "pt-slave-delay"
examines the slave's SHOW SLAVE STATUS to determine the hostname and port for
connecting to the master.

"pt-slave-delay" uses only the MASTER_HOST and MASTER_PORT values from SHOW SLAVE
STATUS for the master connection. It does not use the MASTER_USER value. If you want
to specify a different username for the master than the one you use to connect to the
slave, you should specify the MASTER_DSN option explicitly on the command line.

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

User for login if not current user.

--version
Show version and exit.

--[no]version-check
default: yes

Check for the latest version of Percona Toolkit, MySQL, and other programs.

This is a standard "check for updates automatically" feature, with two additional
features. First, the tool checks the version of other programs on the local system in
addition to its own version. For example, it checks the version of every MySQL server
it connects to, Perl, and the Perl module DBD::mysql. Second, it checks for and warns
about versions with known problems. For example, MySQL 5.5.25 had a critical bug and
was re-released as 5.5.25a.

Any updates or known problems are printed to STDOUT before the tool's normal output.
This feature should never interfere with the normal operation of the tool.

For more information, visit <https://www.percona.com/version-check>.

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

dsn: database; copy: yes

Default database.

· 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. If password contains commas they must be escaped
with a backslash: "exam\,ple"

· P

dsn: port; copy: yes

Port number to use for connection.

· S

dsn: mysql_socket; copy: yes

Socket file to use for connection.

· 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-slave-delay ... > 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.

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