digdeep

凡是过去,皆是序幕。Read the fucking manual and source code.

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mysqldump 是MySQL的一个命令行工具,用于逻辑备份。可以将数据库和表的结构,以及表中的数据分别导出成:create database, create table, insert into的sql语句。当然也可以导出 存储过程,触发器,函数,调度事件(events)。不管是程序员,还是DBA都会经常使用的一个工具。

1. mysqldump --help

mysqldump 的选项很多,我们看一下他的帮助文档:

mysqldump  Ver 10.13 Distrib 5.6.26, for linux-glibc2.5 (i686)
Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Dumping structure and contents of MySQL databases and tables.
Usage: mysqldump [OPTIONS] database [tables]
OR     mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]
OR     mysqldump [OPTIONS] --all-databases [OPTIONS]

Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf 
The following groups are read: mysqldump client
The following options may be given as the first argument:
--print-defaults        Print the program argument list and exit.
--no-defaults           Don't read default options from any option file,
                        except for login file.
--defaults-file=#       Only read default options from the given file #.
--defaults-extra-file=# Read this file after the global files are read.
--defaults-group-suffix=#
                        Also read groups with concat(group, suffix)
--login-path=#          Read this path from the login file.
  -A, --all-databases Dump all the databases. This will be same as --databases
                      with all databases selected.
  -Y, --all-tablespaces 
                      Dump all the tablespaces.
  -y, --no-tablespaces 
                      Do not dump any tablespace information.
  --add-drop-database Add a DROP DATABASE before each create.
  --add-drop-table    Add a DROP TABLE before each create.
                      (Defaults to on; use --skip-add-drop-table to disable.)
  --add-drop-trigger  Add a DROP TRIGGER before each create.
  --add-locks         Add locks around INSERT statements.
                      (Defaults to on; use --skip-add-locks to disable.)
  --allow-keywords    Allow creation of column names that are keywords.
  --apply-slave-statements 
                      Adds 'STOP SLAVE' prior to 'CHANGE MASTER' and 'START
                      SLAVE' to bottom of dump.
  --bind-address=name IP address to bind to.
  --character-sets-dir=name 
                      Directory for character set files.
  -i, --comments      Write additional information.
                      (Defaults to on; use --skip-comments to disable.)
  --compatible=name   Change the dump to be compatible with a given mode. By
                      default tables are dumped in a format optimized for
                      MySQL. Legal modes are: ansi, mysql323, mysql40,
                      postgresql, oracle, mssql, db2, maxdb, no_key_options,
                      no_table_options, no_field_options. One can use several
                      modes separated by commas. Note: Requires MySQL server
                      version 4.1.0 or higher. This option is ignored with
                      earlier server versions.
  --compact           Give less verbose output (useful for debugging). Disables
                      structure comments and header/footer constructs.  Enables
                      options --skip-add-drop-table --skip-add-locks
                      --skip-comments --skip-disable-keys --skip-set-charset.
  -c, --complete-insert 
                      Use complete insert statements.
  -C, --compress      Use compression in server/client protocol.
  -a, --create-options 
                      Include all MySQL specific create options.
                      (Defaults to on; use --skip-create-options to disable.)
  -B, --databases     Dump several databases. Note the difference in usage; in
                      this case no tables are given. All name arguments are
                      regarded as database names. 'USE db_name;' will be
                      included in the output.
  -#, --debug[=#]     This is a non-debug version. Catch this and exit.
  --debug-check       Check memory and open file usage at exit.
  --debug-info        Print some debug info at exit.
  --default-character-set=name 
                      Set the default character set.
  --delayed-insert    Insert rows with INSERT DELAYED.
  --delete-master-logs 
                      Delete logs on master after backup. This automatically
                      enables --master-data.
  -K, --disable-keys  '/*!40000 ALTER TABLE tb_name DISABLE KEYS */; and
                      '/*!40000 ALTER TABLE tb_name ENABLE KEYS */; will be put
                      in the output.
                      (Defaults to on; use --skip-disable-keys to disable.)
  --dump-slave[=#]    This causes the binary log position and filename of the
                      master to be appended to the dumped data output. Setting
                      the value to 1, will printit as a CHANGE MASTER command
                      in the dumped data output; if equal to 2, that command
                      will be prefixed with a comment symbol. This option will
                      turn --lock-all-tables on, unless --single-transaction is
                      specified too (in which case a global read lock is only
                      taken a short time at the beginning of the dump - don't
                      forget to read about --single-transaction below). In all
                      cases any action on logs will happen at the exact moment
                      of the dump.Option automatically turns --lock-tables off.
  -E, --events        Dump events.
  -e, --extended-insert 
                      Use multiple-row INSERT syntax that include several
                      VALUES lists.
                      (Defaults to on; use --skip-extended-insert to disable.)
  --fields-terminated-by=name 
                      Fields in the output file are terminated by the given
                      string.
  --fields-enclosed-by=name 
                      Fields in the output file are enclosed by the given
                      character.
  --fields-optionally-enclosed-by=name 
                      Fields in the output file are optionally enclosed by the
                      given character.
  --fields-escaped-by=name 
                      Fields in the output file are escaped by the given
                      character.
  -F, --flush-logs    Flush logs file in server before starting dump. Note that
                      if you dump many databases at once (using the option
                      --databases= or --all-databases), the logs will be
                      flushed for each database dumped. The exception is when
                      using --lock-all-tables or --master-data: in this case
                      the logs will be flushed only once, corresponding to the
                      moment all tables are locked. So if you want your dump
                      and the log flush to happen at the same exact moment you
                      should use --lock-all-tables or --master-data with
                      --flush-logs.
  --flush-privileges  Emit a FLUSH PRIVILEGES statement after dumping the mysql
                      database.  This option should be used any time the dump
                      contains the mysql database and any other database that
                      depends on the data in the mysql database for proper
                      restore. 
  -f, --force         Continue even if we get an SQL error.
  -?, --help          Display this help message and exit.
  --hex-blob          Dump binary strings (BINARY, VARBINARY, BLOB) in
                      hexadecimal format.
  -h, --host=name     Connect to host.
  --ignore-table=name Do not dump the specified table. To specify more than one
                      table to ignore, use the directive multiple times, once
                      for each table.  Each table must be specified with both
                      database and table names, e.g.,
                      --ignore-table=database.table.
  --include-master-host-port 
                      Adds 'MASTER_HOST=<host>, MASTER_PORT=<port>' to 'CHANGE
                      MASTER TO..' in dump produced with --dump-slave.
  --insert-ignore     Insert rows with INSERT IGNORE.
  --lines-terminated-by=name 
                      Lines in the output file are terminated by the given
                      string.
  -x, --lock-all-tables 
                      Locks all tables across all databases. This is achieved
                      by taking a global read lock for the duration of the
                      whole dump. Automatically turns --single-transaction and
                      --lock-tables off.
  -l, --lock-tables   Lock all tables for read.
                      (Defaults to on; use --skip-lock-tables to disable.)
  --log-error=name    Append warnings and errors to given file.
  --master-data[=#]   This causes the binary log position and filename to be
                      appended to the output. If equal to 1, will print it as a
                      CHANGE MASTER command; if equal to 2, that command will
                      be prefixed with a comment symbol. This option will turn
                      --lock-all-tables on, unless --single-transaction is
                      specified too (in which case a global read lock is only
                      taken a short time at the beginning of the dump; don't
                      forget to read about --single-transaction below). In all
                      cases, any action on logs will happen at the exact moment
                      of the dump. Option automatically turns --lock-tables
                      off.
  --max-allowed-packet=# 
                      The maximum packet length to send to or receive from
                      server.
  --net-buffer-length=# 
                      The buffer size for TCP/IP and socket communication.
  --no-autocommit     Wrap tables with autocommit/commit statements.
  -n, --no-create-db  Suppress the CREATE DATABASE ... IF EXISTS statement that
                      normally is output for each dumped database if
                      --all-databases or --databases is given.
  -t, --no-create-info 
                      Don't write table creation info.
  -d, --no-data       No row information.
  -N, --no-set-names  Same as --skip-set-charset.
  --opt               Same as --add-drop-table, --add-locks, --create-options,
                      --quick, --extended-insert, --lock-tables, --set-charset,
                      and --disable-keys. Enabled by default, disable with
                      --skip-opt.
  --order-by-primary  Sorts each table's rows by primary key, or first unique
                      key, if such a key exists.  Useful when dumping a MyISAM
                      table to be loaded into an InnoDB table, but will make
                      the dump itself take considerably longer.
  -p, --password[=name] 
                      Password to use when connecting to server. If password is
                      not given it's solicited on the tty.
  -P, --port=#        Port number to use for connection.
  --protocol=name     The protocol to use for connection (tcp, socket, pipe,
                      memory).
  -q, --quick         Don't buffer query, dump directly to stdout.
                      (Defaults to on; use --skip-quick to disable.)
  -Q, --quote-names   Quote table and column names with backticks (`).
                      (Defaults to on; use --skip-quote-names to disable.)
  --replace           Use REPLACE INTO instead of INSERT INTO.
  -r, --result-file=name 
                      Direct output to a given file. This option should be used
                      in systems (e.g., DOS, Windows) that use carriage-return
                      linefeed pairs (\r\n) to separate text lines. This option
                      ensures that only a single newline is used.
  -R, --routines      Dump stored routines (functions and procedures).
  --set-charset       Add 'SET NAMES default_character_set' to the output.
                      (Defaults to on; use --skip-set-charset to disable.)
  --set-gtid-purged[=name] 
                      Add 'SET @@GLOBAL.GTID_PURGED' to the output. Possible
                      values for this option are ON, OFF and AUTO. If ON is
                      used and GTIDs are not enabled on the server, an error is
                      generated. If OFF is used, this option does nothing. If
                      AUTO is used and GTIDs are enabled on the server, 'SET
                      @@GLOBAL.GTID_PURGED' is added to the output. If GTIDs
                      are disabled, AUTO does nothing. If no value is supplied
                      then the default (AUTO) value will be considered.
  --single-transaction 
                      Creates a consistent snapshot by dumping all tables in a
                      single transaction. Works ONLY for tables stored in
                      storage engines which support multiversioning (currently
                      only InnoDB does); the dump is NOT guaranteed to be
                      consistent for other storage engines. While a
                      --single-transaction dump is in process, to ensure a
                      valid dump file (correct table contents and binary log
                      position), no other connection should use the following
                      statements: ALTER TABLE, DROP TABLE, RENAME TABLE,
                      TRUNCATE TABLE, as consistent snapshot is not isolated
                      from them. Option automatically turns off --lock-tables.
  --dump-date         Put a dump date to the end of the output.
                      (Defaults to on; use --skip-dump-date to disable.)
  --skip-opt          Disable --opt. Disables --add-drop-table, --add-locks,
                      --create-options, --quick, --extended-insert,
                      --lock-tables, --set-charset, and --disable-keys.
  -S, --socket=name   The socket file to use for connection.
  --secure-auth       Refuse client connecting to server if it uses old
                      (pre-4.1.1) protocol.
                      (Defaults to on; use --skip-secure-auth to disable.)
  --ssl               Enable SSL for connection (automatically enabled with
                      other flags).
  --ssl-ca=name       CA file in PEM format (check OpenSSL docs, implies
                      --ssl).
  --ssl-capath=name   CA directory (check OpenSSL docs, implies --ssl).
  --ssl-cert=name     X509 cert in PEM format (implies --ssl).
  --ssl-cipher=name   SSL cipher to use (implies --ssl).
  --ssl-key=name      X509 key in PEM format (implies --ssl).
  --ssl-crl=name      Certificate revocation list (implies --ssl).
  --ssl-crlpath=name  Certificate revocation list path (implies --ssl).
  --ssl-verify-server-cert 
                      Verify server's "Common Name" in its cert against
                      hostname used when connecting. This option is disabled by
                      default.
  -T, --tab=name      Create tab-separated textfile for each table to given
                      path. (Create .sql and .txt files.) NOTE: This only works
                      if mysqldump is run on the same machine as the mysqld
                      server.
  --tables            Overrides option --databases (-B).
  --triggers          Dump triggers for each dumped table.
                      (Defaults to on; use --skip-triggers to disable.)
  --tz-utc            SET TIME_ZONE='+00:00' at top of dump to allow dumping of
                      TIMESTAMP data when a server has data in different time
                      zones or data is being moved between servers with
                      different time zones.
                      (Defaults to on; use --skip-tz-utc to disable.)
  -u, --user=name     User for login if not current user.
  -v, --verbose       Print info about the various stages.
  -V, --version       Output version information and exit.
  -w, --where=name    Dump only selected records. Quotes are mandatory.
  -X, --xml           Dump a database as well formed XML.
  --plugin-dir=name   Directory for client-side plugins.
  --default-auth=name Default authentication client-side plugin to use.

Variables (--variable-name=value)
and boolean options {FALSE|TRUE}  Value (after reading options)
--------------------------------- ----------------------------------------
all-databases                     FALSE
all-tablespaces                   FALSE
no-tablespaces                    FALSE
add-drop-database                 FALSE
add-drop-table                    TRUE
add-drop-trigger                  FALSE
add-locks                         TRUE
allow-keywords                    FALSE
apply-slave-statements            FALSE
bind-address                      (No default value)
character-sets-dir                (No default value)
comments                          TRUE
compatible                        (No default value)
compact                           FALSE
complete-insert                   FALSE
compress                          FALSE
create-options                    TRUE
databases                         FALSE
debug-check                       FALSE
debug-info                        FALSE
default-character-set             utf8
delayed-insert                    FALSE
delete-master-logs                FALSE
disable-keys                      TRUE
dump-slave                        0
events                            FALSE
extended-insert                   TRUE
fields-terminated-by              (No default value)
fields-enclosed-by                (No default value)
fields-optionally-enclosed-by     (No default value)
fields-escaped-by                 (No default value)
flush-logs                        FALSE
flush-privileges                  FALSE
force                             FALSE
hex-blob                          FALSE
host                              (No default value)
include-master-host-port          FALSE
insert-ignore                     FALSE
lines-terminated-by               (No default value)
lock-all-tables                   FALSE
lock-tables                       TRUE
log-error                         (No default value)
master-data                       0
max-allowed-packet                25165824
net-buffer-length                 1046528
no-autocommit                     FALSE
no-create-db                      FALSE
no-create-info                    FALSE
no-data                           FALSE
order-by-primary                  FALSE
port                              0
quick                             TRUE
quote-names                       TRUE
replace                           FALSE
routines                          FALSE
set-charset                       TRUE
single-transaction                FALSE
dump-date                         TRUE
socket                            /var/lib/mysql/mysql.sock
secure-auth                       TRUE
ssl                               FALSE
ssl-ca                            (No default value)
ssl-capath                        (No default value)
ssl-cert                          (No default value)
ssl-cipher                        (No default value)
ssl-key                           (No default value)
ssl-crl                           (No default value)
ssl-crlpath                       (No default value)
ssl-verify-server-cert            FALSE
tab                               (No default value)
triggers                          TRUE
tz-utc                            TRUE
user                              (No default value)
verbose                           FALSE
where                             (No default value)
plugin-dir                        (No default value)
default-auth                      (No default value)
mysqldump --help

总体看来,帮助文档分成了两个部分。前一个部分是对各种选项的说明,后一个部分是mysqldump的各种选项的默认值。

mysqldump拥有超多的选项,这样说明它很灵活,功能强大。为了好理解,可以将他的众多的选项和参数,根据他们的功能分为几个类别来介绍。

在此之前,我们还要搞清楚mysqldump的所有的默认选项的值,它们的含义。

2. mysqldump 默认选项:

Variables (--variable-name=value)
and boolean options {FALSE|TRUE}  Value (after reading options)
--------------------------------- ----------------------------------------
all-databases                     FALSE
all-tablespaces                   FALSE
no-tablespaces                    FALSE
add-drop-database                 FALSE
add-drop-table                    TRUE
add-drop-trigger                  FALSE
add-locks                         TRUE
allow-keywords                    FALSE
apply-slave-statements            FALSE
bind-address                      (No default value)
character-sets-dir                (No default value)
comments                          TRUE
compatible                        (No default value)
compact                           FALSE
complete-insert                   FALSE
compress                          FALSE
create-options                    TRUE
databases                         FALSE
debug-check                       FALSE
debug-info                        FALSE
default-character-set             utf8
delayed-insert                    FALSE
delete-master-logs                FALSE
disable-keys                      TRUE
dump-slave                        0
events                            FALSE
extended-insert                   TRUE
fields-terminated-by              (No default value)
fields-enclosed-by                (No default value)
fields-optionally-enclosed-by     (No default value)
fields-escaped-by                 (No default value)
flush-logs                        FALSE
flush-privileges                  FALSE
force                             FALSE
hex-blob                          FALSE
host                              (No default value)
include-master-host-port          FALSE
insert-ignore                     FALSE
lines-terminated-by               (No default value)
lock-all-tables                   FALSE
lock-tables                       TRUE
log-error                         (No default value)
master-data                       0
max-allowed-packet                25165824
net-buffer-length                 1046528
no-autocommit                     FALSE
no-create-db                      FALSE
no-create-info                    FALSE
no-data                           FALSE
order-by-primary                  FALSE
port                              0
quick                             TRUE
quote-names                       TRUE
replace                           FALSE
routines                          FALSE
set-charset                       TRUE
single-transaction                FALSE
dump-date                         TRUE
socket                            /var/lib/mysql/mysql.sock
secure-auth                       TRUE
ssl                               FALSE
ssl-ca                            (No default value)
ssl-capath                        (No default value)
ssl-cert                          (No default value)
ssl-cipher                        (No default value)
ssl-key                           (No default value)
ssl-crl                           (No default value)
ssl-crlpath                       (No default value)
ssl-verify-server-cert            FALSE
tab                               (No default value)
triggers                          TRUE
tz-utc                            TRUE
user                              (No default value)
verbose                           FALSE
where                             (No default value)
plugin-dir                        (No default value)
default-auth                      (No default value)
mysqldump

这些默认值,有的是 false, 有的是 true,有的没有默认值。

我们要关注的是 默认为 true,也就是 mysqldump 默认给我打开的选择,它们的具体含义如下

add-drop-table                    TRUE 表示在生成表结构语句之前,生对应的 DROP TABLE IF EXISTS `table_name`; 语句
add-locks                         TRUE 表示在生表中数据的 insert into `table_name` values(...) 之前生成 LOCK TABLES `tab` WRITE;语句
comments                          TRUE 表示生成备注,就是所有 -- 开头的说明,比如:-- Dumping data for  for table `tab`. 最好还是启用;
create-options                    TRUE 表示在生表结构时会生成:ENGINE=InnoDB AUTO_INCREMENT=827 DEFAULT CHARSET=utf8; 附加建表选项
default-character-set             utf8 指定语句:/*!40101 SET NAMES utf8 */;中的字符集;可能你需要改成 --default-character-set=utf8mb4
disable-keys                      TRUE 表示生产 insert 语句之前,生成:/*!40000 ALTER TABLE `tbl` DISABLE KEYS */; 可以加快insert速度;
extended-insert                   TRUE 表示生产的insert是insert into `tbl` values(...),(...),数据行按照net-buffer-length分割合并成多个batch insert
lock-tables                       TRUE 表示在导出的过程中会锁定所有表;
max-allowed-packet                25165824 最大支持 24M 的数据包;
net-buffer-length                 1046528  1M大小的socket buffer
quick                             TRUE 表示在导出语句时,不缓存,直接输出到控制台或者文件中;
quote-names                       TRUE 表示对表名和列名使用 `` 符号包裹;防止它们是关键字时会出错;
set-charset                       TRUE default-character-set=utf8指定字符集,而--set-charset=1/0 表示是否生成/*!40101 SET NAMES utf8 */; 
dump-date                         TRUE 表示是否在导出文件的末尾生成导出时间:-- Dump completed on 2015-09-15 11:15:10 
secure-auth                       TRUE 表示登录判断密码时使用新的加密算法,拒绝就的加密算法
triggers                          TRUE 表示生触发器脚本;
tz-utc                            TRUE 表示是否生成:/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */; /*!40103 SET TIME_ZONE='+00:00' */;

如果要关闭这些打开的默认选项时,需要明确指定:mysqldump -uxxx -p aazj --extended-insert=0 Users > Users.sql; =0 表示关闭选项。

上面这些默认选项,最好结合一个例子来理解:

-- MySQL dump 10.13  Distrib 5.6.26, for linux-glibc2.5 (i686)
--
-- Host: localhost    Database: gs
-- ------------------------------------------------------
-- Server version    5.6.26-log

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

--
-- Current Database: `gs`
--

CREATE DATABASE /*!32312 IF NOT EXISTS*/ `gs` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin */;

USE `gs`;

--
-- Table structure for table `user`
--

DROP TABLE IF EXISTS `user`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(30) COLLATE utf8mb4_bin DEFAULT NULL,
  `sex` tinyint(4) DEFAULT NULL,
  `phone` varchar(20) COLLATE utf8mb4_bin DEFAULT NULL,
  `addr` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `user`
--

LOCK TABLES `user` WRITE;
/*!40000 ALTER TABLE `user` DISABLE KEYS */;
INSERT INTO `user` VALUES (1,'yuanfang',1,'14465463786','hangzhou'),(2,'Andy',0,'14465463786','beijing'),(3,'peter',0,'14465463786','Hongkong');
/*!40000 ALTER TABLE `user` ENABLE KEYS */;
UNLOCK TABLES;
/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

-- Dump completed on 2015-10-22 10:16:37
mysqldump

2. mysqldump 登录服务器的相关选项

Default options are read from the following files in the given order:

/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf


The following groups are read: mysqldump client
The following options may be given as the first argument:
--no-defaults           Don't read default options from any option file, except for login file.
--defaults-file=#       Only read default options from the given file #.
--defaults-extra-file=# Read this file after the global files are read.
--defaults-group-suffix=# Also read groups with concat(group, suffix)
--login-path=#          Read this path from the login file.

1)mysqldump 作为一个客户端工具,它会去上诉目录中寻找 my.cnf 文件,然后读取该文件中 [mysqldump] 和 [client] 下面的选项

2)那些 defaults 相关的选项都是为了另外指定 配置文件和登录文件,极少使用;

  -u, --user=name     User for login if not current user.

  -p, --password[=name] Password to use when connecting to server. If password is not given it's solicited on the tty.

  -h, --host=name     Connect to host.

  -P, --port=#        Port number to use for connection.
  --protocol=name     The protocol to use for connection (tcp, socket, pipe, memory).

  --max-allowed-packet=#  The maximum packet length to send to or receive from server.
  --net-buffer-length=#      The buffer size for TCP/IP and socket communication.

3)这几个选项指定 登录的用户名,密码,mysqld IP地址,端口,连接使用的协议等等。

    一般常用的是 -h192.168.2.xx -uxxx -p ,如果mysqld默认端口不是3306,则需要使用 -Pxxx 指定端口.

    --max-allowed-packet 我们一般配置在my.cnf中。--net-buffer-length 是为了优化网络连接的socket buffer.

使用示例: mysqldump -h192.168.1.20 -uxxx -p -P3057

3. mysqldump 选择备份内容的相关选项

我们可以选择备份所有数据库,某几个数据库,某一个数据库,某一个数据库中的某几个表,某一个数据库中的一个表;

可以选择是否备份 存储过程和函数,触发器,调度事件.

1)选择导出的数据库 和 表:

-A, --all-databases Dump all the databases. This will be same as --databases with all databases selected.

-B, --databases     Dump several databases. Note the difference in usage; in this case no tables are given. All name arguments are

                            regarded as database names. 'USE db_name;' will be included in the output.

database [tables]   导出数据库 database 中的表结构 和 表中数据;

2)选择是否导出 建库,建表语句,是否导出 表中的数据:

-n, --no-create-db  Suppress the CREATE DATABASE ... IF NOT EXISTS statement that normally is output for each dumped database if 

                             --all-databases or --databases is given. (不导出建库语句: CREATE DATABASE,也就是不导库结构)

-t, --no-create-info Don't write table creation info. (不导出建表语句)

-d, --no-data         No row information. (不导出数据,有时我们仅仅需要导出表结构,也就是建表语句就行了)

3)选择是否导出 存储过程和函数,触发器,调度事件:

-R, --routines      Dump stored routines (functions and procedures). (导出存储过程和函数)

--triggers            Dump triggers for each dumped table. (Defaults to on; use --skip-triggers to disable.) (导出触发器)

--skip-triggers     不导出触发器

-E, --events        Dump events. 导出调度事件(根据备份的目的进行选择,如果是搭建slave,那么就不要导出events.)

4)指定不导出 某个库的某个表:

--ignore-table=name   Do not dump the specified table. To specify more than one table to ignore, use the directive multiple times,

                                 once for each table.  Each table must be specified with both database and table names,

                                 e.g.,  --ignore-table=database.table. (在导出数据库时,排除某个或者某几个表不导出)

5) 按照 where 条件导出:

   -w, --where='where_condition' Dump only selected records. Quotes are mandatory.

6)使用示例:

Dumping structure and contents of MySQL databases and tables.
Usage: mysqldump [OPTIONS] database [tables]
OR       mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]
OR       mysqldump [OPTIONS] --all-databases [OPTIONS]

1> 导出单表的结构和数据:mysqldump -uxxx -p db1 tb1 > tb1.sql; 导出数据库 db1 中的 表 tb1 的表结构 和 表中数据;

2> 导出多表的结构和数据:mysqldump -uxxx -p db1 tb1 tb2 > tb1_tb2.sql; 导出数据库 db1 中的 表 tb1、tb2 的表结构 和 表中数据;

3> 导出单表的结构:mysqldump -uxxx -p --no-data db1 tb1 > tb1.sql; 导出数据库 db1 中的 表 tb1 的表结构; 其实也可以使用: show create table tb1

4> 我们无法使用 mysqldump 到达 只导出某个或某几个表的数据,而不导出建表语句的目的。

     但是我们可以使用 select * from table into outfile 'file.sql', 比如:select * from Users into outfile '/tmp/Users.sql'; 注意需要对目录的写权限。

5> 导出单个库中库结构、表结构、表数据:mysqldump -uxxx -p --databases db1 > db1.sql

6> 导出多个库中库结构、表结构、表数据:mysqldump -uxxx -p --databases db1 db2 > db1_db2.sql

7> 导出单个库中库结构、表结构、不要表数据:mysqldump -uxxx -p --no-data --databases db1 > db1.sql

8> 导出单个库中数据,不要库结构和表结构:mysqldump -uxxx -p --no-create-db --no-create-info --databases db1 > db1.sql

9> 导出多个库中库结构、表结构、不要表数据:mysqldump -uxxx -p --no-data --databases db1 db2 > db1_db2.sql

10> 导出数据库中所有 库 的库结构,表结构,数据:mysqldump -uxxx -p --all-databases > all.sql

11> 导出数据库中所有 库 的库结构,表结构,不要数据:mysqldump -uxxx -p --all-databases --no-data > all.sql

12> 导出单个库中库结构、表结构、表数据,排除某个表:mysqldump -uxxx -p --databases db1 --ignore-table=db1.test > db1.sql

4. mysqldump 事务 和 数据一致性(锁) 的相关选项

在使用mysqldump逻辑备份时,事务和数据一致性的选项时至关重要的。

1) --single-transaction
      Creates a consistent snapshot by dumping all tables in a single transaction. Works ONLY for tables stored in storage engines which

      support multiversioning (currently only InnoDB does); the dump is NOT guaranteed to be consistent for other storage engines.

      While a --single-transaction dump is in process, to ensure a valid dump file (correct table contents and binary log position), no other

      connection should use the following statements: ALTER TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE, as consistent

      snapshot is not isolated from them. Option automatically turns off --lock-tables.

     --single-transaction 可以得到一致性的导出结果。他是通过将导出行为放入一个事务中达到目的的。

     它有一些要求:只能是 innodb 引擎;导出的过程中,不能有任何人执行 alter table, drop table, rename table, truncate table等DDL语句

     实际上DDL会被事务所阻塞,因为事务持有表的metadata lock 的共享锁,而DDL会申请metadata lock的互斥锁,所以阻塞了。

     --single-transaction 会自动关闭 --lock-tables 选项;上面我们说到mysqldump默认会打开了--lock-tables,它会在导出过程中锁定所有表。

    因为 --single-transaction 会自动关闭--lock-tables,所以单独使用--single-transaction是不会使用锁的。与 --master-data 合用才有锁。

2)--lock-tables

     该选项默认打开的,上面已经说到了。它的作用是在导出过程中锁定所有表。--single-transaction 和 --lock-all-tables 都会将该选项关闭。

3)--lock-all-tables
       Locks all tables across all databases. This is achieved by taking a global read lock for the duration of the whole dump.
       Automatically turns --single-transaction and --lock-tables off. 启用该选项,会自动关闭 --single-transaction 和 --lock-tables.

上面三个选项中,只有 --lock-tables 默认是打开的;打开 --single-transaction 或者 打开 --lock-all-tables 都将关闭 --lock-tables. 而--lock-all-tables会自动关闭 --single-transaction 和 --lock-tables。所以三者是互斥的。我们应该一次只启用其中一个选项。

4)--flush-logs   

        Flush logs file in server before starting dump. Note that if you dump many databases at once (using the option --databases= or

        --all-databases), the logs will be flushed for each database dumped. The exception is when using --lock-all-tables or

        --master-data: in this case the logs will be flushed only once, corresponding to the moment all tables are locked. So if you want your

       dump and the log flush to happen at the same exact moment you should use --lock-all-tables or --master-data with --flush-logs.

       为了获得导出数据和刷新日志的一致性(同时发生),必须将 --flush-logs 选项和 --lock-all-tables 或者 --master-data 一起使用:

       mysqldump --flush-logs --lock-all-tables;  mysqldump --flush-logs --master-data=2

5)--flush-privileges 

      Emit a FLUSH PRIVILEGES statement after dumping the mysql database.  This option should be used any time the dump contains the

      mysql database and any other database that depends on the data in the mysql database for proper restore.

      如何导出包含了mysql数据,就应该启用该选项。该选项会在导出的 mysql 数据库的后面加上 flush privileges 语句,因为在向mysql数据库inert了语句

      之后,必须使用 flush privileges,不然权限不生效。下面是例子:

6)  --master-data[=#]  

       This causes the binary log position and filename to be appended to the output. If equal to 1, will print it as a CHANGE MASTER

       command; if equal to 2, that command will be prefixed with a comment symbol. This option will turn --lock-all-tables on, unless

       --single-transaction is specified too (in which case a global read lock is only taken a short time at the beginning of the dump; don't
       forget to read about --single-transaction below). In all cases, any action on logs will happen at the exact moment of the dump.

       Option automatically turns --lock-tables off.

所以为了获得一致性的备份数据和在备份是同时刷新binary日志,我们应该如下结合使用这些选项(完美组合——其实并不完美!!!因为:a global read lock is only taken a short time at the beginning of the dump,会导致 Waiting for table flush):

mysqldump -uroot -pxxxxxx --single-transaction --master-data=2 --set-gtid-purged=OFF  xxdb --where "1=1 limit 100000" > xxdb_10W.sql

(其中 --flush-logs 不是必须的; 搭建slave时,不要导出events,但是需要导出rountines.)

其中被 --master-data 打开的 --lock-all-tables 选项,又被 --single-transaction 关闭掉了--flush-logs 借助于 --master-data 可以达到即使一次导出多个数据库时,其 flush 的二进制日志也是在同一个时间点的,不是每一个数据库flush一次的。并且这个时间点 和 --master-data 记录的 binary log position 和 binary log file是同一个时间点,这些都是利用了 --single-transaction 和 --master-data 合用时短暂的使用一个全局的读锁来达到目的的

5. mysqldump 复制 的相关选项

1)  --master-data[=#]  

       This causes the binary log position and filename to be appended to the output. If equal to 1, will print it as a CHANGE MASTER

       command; if equal to 2, that command will be prefixed with a comment symbol. This option will turn --lock-all-tables on, unless

       --single-transaction is specified too (in which case a global read lock is only taken a short time at the beginning of the dump;

       don't forget to read about --single-transaction below). In all cases, any action on logs will happen at the exact moment of the dump.

       Option automatically turns --lock-tables off.

       该选项,上面已经介绍了。--master-data=1 表示会导出 change master to 语句,--master-data=2 该语句放在注释中,默认是为 0 。

       一般会和 --single-transaction一起使用,用于搭建master-slave环境。

下面是 --master-data=1 和 --master-data=2 的比较:

在导出文件的前30行左右可以看到 change master to 语句。可以使用 head -n 30 db1.sql 查看

2)  --dump-slave[=#]   

      This causes the binary log position and filename of the master to be appended to the dumped data output. Setting the value to 1, will

      printit as a CHANGE MASTER command in the dumped data output; if equal to 2, that command will be prefixed with a comment

      symbol. This option will turn --lock-all-tables on, unless --single-transaction is specified too (in which case a global read lock is only

      taken a short time at the beginning of the dump - don't forget to read about --single-transaction below). In all cases any action on

      logs will happen at the exact moment of the dump.Option automatically turns --lock-tables off.

      --dump-slave 和 --master-data 几乎一样。区别只是--dump-slave用于slave建立下一级的slave;而 --master-data用于master建立slave;

      如果在 master 上使用 --dump-slave 会报错:mysqldump: Couldn't execute 'START SLAVE': The server is not configured as slave;

3) --apply-slave-statements
       Adds 'STOP SLAVE' prior to 'CHANGE MASTER' and 'START SLAVE' to bottom of dump.

       在 change master 导出 stop slave 语句, 在 change master 之后导出 start slave语句。其实是一个自动化的处理。和 --master-data=1 类似。

如下图所示:开头有 stop slave, 结尾有 start slave语句:

4)--include-master-host-port
      Adds 'MASTER_HOST=<host>, MASTER_PORT=<port>' to 'CHANGE MASTER TO..' in dump produced with --dump-slave.

      该选择要结合 --dump-slave=1/2 使用。会在导出中加入 host。

5)--include-master-host-port
     Adds 'MASTER_HOST=<host>, MASTER_PORT=<port>' to 'CHANGE MASTER TO..' in dump produced with --dump-slave.

     该选择要结合 --dump-slave=1/2 使用。会在导出中加入mysql的 port。

6)--delete-master-logs
     Delete logs on master after backup. This automatically enables --master-data.

     在备份之后,删除 master上的binary log。该选项会自动打开 --master-data 选项(等于2)。该选项一般不用。日志一般不能随便删除。

7)--set-gtid-purged[=name]
     Add 'SET @@GLOBAL.GTID_PURGED' to the output. Possible values for this option are ON, OFF and AUTO. If ON is used and GTIDs

     are not enabled on the server, an error is generated. If OFF is used, this option does nothing. If AUTO is used and GTIDs are enabled

     on the server, 'SET @@GLOBAL.GTID_PURGED' is added to the output. If GTIDs are disabled, AUTO does nothing. If no value is

     supplied then the default (AUTO) value will be considered.

     该选项用于启用了GTID特性的环境。

6. mysqldump 字符集 的相关选项

1)--set-charset      

     Add 'SET NAMES default_character_set' to the output.  (Defaults to on; use --skip-set-charset to disable.)

    --set-charset=1/0 开启和关闭。也可以使用 --skip-set-charset 关闭。

   该选项我们上面已经说到了。表示是否生成 /*!40101 SET NAMES utf8 */;

2)-N, --no-set-names 

     Same as --skip-set-charset. 关闭 --set-charset. 不生成 /*!40101 SET NAMES utf8 */; 语句。

3)--default-character-set=name
     Set the default character set.

     该选项上面也涉及到了。指定语句:/*!40101 SET NAMES utf8 */;中的字符集;可能你需要改成 --default-character-set=utf8mb4

7. mysqldump 控制是否生成 DDL 语句 的相关选项

  --add-drop-database  Add a DROP DATABASE before each create.
  --add-drop-table        Add a DROP TABLE before each create.  (Defaults to on; use --skip-add-drop-table to disable.)
  --add-drop-trigger      Add a DROP TRIGGER before each create.

  --no-create-db,-n

  --no-create-info,-t

8. mysqldump 导出格式 的相关选项

1)--compatible=name  

     Change the dump to be compatible with a given mode. By default tables are dumped in a format optimized for MySQL.

     Legal modes are: ansi, mysql323, mysql40, postgresql, oracle, mssql, db2, maxdb, no_key_options, no_table_options,

     no_field_options. One can use several modes separated by commas. Note: Requires MySQL server version 4.1.0 or higher.

     This option is ignored with earlier server versions.

     导出sql语句的兼容格式。如果我们需要从MySQL导出,然后导入到其它数据库,则可使用该选项。--compatible=oracle/postgresql/mssql

2)-Q, --quote-names  

     Quote table and column names with backticks (`). (Defaults to on; use --skip-quote-names to disable.)

     将表名和列名使用 ``包裹。以防他们是关键字时报错。

9. mysqldump 错误处理的相关选项

1)-f, --force              Continue even if we get an SQL error.

2)--log-error=name    Append warnings and errors to given file.

10. mysqldump 实现原理

为了探求 mysqldump 的备份是如何实现的,我们需要在 my.cnf 中的[mysqld] 参数段加入:

general_log=on
general_log_file=general.log

这样我们就可以通过观察 general.log 的输出,来了解 mysqldump 的备份是如何实现的。

1)--lock-tables 是如何实现的:

先执行:mysqldump -uroot -p --databases gs --lock-tables > gs_l.sql, 然后查看 general.log:

                    3 Init DB   gs
                    3 Query     SHOW CREATE DATABASE IF NOT EXISTS `gs`
                    3 Query     show tables
                    3 Query     LOCK TABLES `tb1` READ /*!32311 LOCAL */,`user` READ /*!32311 LOCAL */
                    3 Query     show table status like 'tb1'
                    3 Query     SET SQL_QUOTE_SHOW_CREATE=1
                    3 Query     SET SESSION character_set_results = 'binary'
                    3 Query     show create table `tb1`
                    3 Query     SET SESSION character_set_results = 'utf8'
                    3 Query     show fields from `tb1`
                    3 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`
                    3 Query     SET SESSION character_set_results = 'binary'
                    3 Query     use `gs`
                    3 Query     select @@collation_database
                    3 Query     SHOW TRIGGERS LIKE 'tb1'
                    3 Query     SET SESSION character_set_results = 'utf8'
                    3 Query     show table status like 'user'
                    3 Query     SET SQL_QUOTE_SHOW_CREATE=1
                    3 Query     SET SESSION character_set_results = 'binary'
                    3 Query     show create table `user`
                    3 Query     SET SESSION character_set_results = 'utf8'
                    3 Query     show fields from `user`
                    3 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `user`
                    3 Query     SET SESSION character_set_results = 'binary'
                    3 Query     use `gs`
                    3 Query     select @@collation_database
                    3 Query     SHOW TRIGGERS LIKE 'user'
                    3 Query     SET SESSION character_set_results = 'utf8'
                    3 Query     UNLOCK TABLES
                    3 Quit

1> 第一步: SHOW CREATE DATABASE IF NOT EXISTS `gs`; 导出了建库语句;

2> 第二步:show tables; 获得数据库中所有表名,然后锁住:LOCK TABLES `tb1` READ /*!32311 LOCAL */,`user` READ /*!32311 LOCAL */

                使用的是 lock table tb1 read local, tb2 read local, tb3 read local; 语句

3> 第三步:show create table 'tb1'; 导出了 tb1 的建表语句;

4> 第四步:show fields from `tb1`; SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`; 导出了表中的数据;

......

5> 最后导出了 trigger, 最后的最后 unlock tables; 结束。

可以看到 --lock-tables 在导出一个数据库时,会在整个导出过程 lock read local 所有的表。该锁不会阻止其它session读和插入

2)--lock-all-tables 的实现:

先执行:mysqldump -uroot -p --databases gs --lock-all-tables > gs_l.sql, 在查看 general.log:

151022 14:34:13     4 Connect   root@localhost on
                    4 Query     /*!40100 SET @@SQL_MODE='' */
                    4 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    4 Query     FLUSH TABLES
                    4 Query     FLUSH TABLES WITH READ LOCK
                    4 Query     SHOW VARIABLES LIKE 'gtid\_mode'
                    ... ...
                    4 Init DB   gs
                    4 Query     SHOW CREATE DATABASE IF NOT EXISTS `gs`
                    4 Query     show tables
                    ... ...4 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`
                    4 Query     SET SESSION character_set_results = 'binary'
                    4 Query     use `gs`
                    4 Query     select @@collation_database
                    ... ...
                    4 Query     show fields from `user`
                    4 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `user`
                    4 Query     SET SESSION character_set_results = 'binary'
                    4 Query     use `gs`
                    4 Query     select @@collation_database
                    4 Query     SHOW TRIGGERS LIKE 'user'
                    4 Query     SET SESSION character_set_results = 'utf8'
                    4 Quit

它的实现使用了 FLUSH TABLES; FLUSH TABLES WITH READ LOCK; 语句。在最后没有看到解锁语句。

它请求发起一个全局的读锁,会阻止对所有表的写入操作,以此来确保数据的一致性。备份完成后,该会话断开,会自动解锁。

3)--single-transaction 的实现:

先执行: mysqldump -uroot -p --databases gs --single-transaction > gs_l.sql,在查看 general.log:

151022 14:41:34     5 Connect   root@localhost on
                    5 Query     /*!40100 SET @@SQL_MODE='' */
                    5 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    5 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
                    5 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
                    5 Query     SHOW VARIABLES LIKE 'gtid\_mode'
                    5 Query     UNLOCK TABLES
                    ... ...
                    5 Init DB   gs
                    5 Query     SHOW CREATE DATABASE IF NOT EXISTS `gs`
                    5 Query     SAVEPOINT sp
                    ......
                    5 Query     show create table `tb1`
                    ......5 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`
                   ......
                    5 Query     ROLLBACK TO SAVEPOINT sp
                   ......
                    5 Query     show create table `user`
                    .....5 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `user`
                    ......
                    5 Query     ROLLBACK TO SAVEPOINT sp
                    5 Query     RELEASE SAVEPOINT sp
                    5 Quit

基本过程是:

1> 先改变事务隔离级别:SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ

2> 开始事务:START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */

3> unlock tables;

4> 导出建库语句; SHOW CREATE DATABASE IF NOT EXISTS `gs`

5> 打开一个 savepoint: SAVEPOINT sp;

6> 导出 表 tb1 的结构和数据;

7> ROLLBACK TO SAVEPOINT sp; 回滚到savepoint;

对其它表重复该过程;

8> 最后 realease savepoint p; 释放savepoint;

整个过程,没有任何锁。RR隔离级别保证在事务中只读取本事务之前的一致性的数据。 rollback to savepoint sp; 保证了对数据库中的数据没有影响。

4)--master-data 的实现:

先执行:mysqldump -uroot -p --databases gs --master-data=1 > gs_l.sql,在查看general.log:

151022 14:57:45     6 Connect   root@localhost on
                    6 Query     /*!40100 SET @@SQL_MODE='' */
                    6 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    6 Query     FLUSH /*!40101 LOCAL */ TABLES
                    6 Query     FLUSH TABLES WITH READ LOCK
                    6 Query     SHOW VARIABLES LIKE 'gtid\_mode'
                    6 Query     SHOW MASTER STATUS

发现了 --lock-all-tables一样,就多了一句:show master status;

5)--single-transaction 和 --master-data 结合使用:

先执行:mysqldump -uroot -p --databases gs --master-data=1 > gs_l.sql,在查看general.log:

151022 15:00:56     7 Connect   root@localhost on
                    7 Query     /*!40100 SET @@SQL_MODE='' */
                    7 Query     /*!40103 SET TIME_ZONE='+00:00' */
                    7 Query     FLUSH /*!40101 LOCAL */ TABLES
                    7 Query     FLUSH TABLES WITH READ LOCK
                    7 Query     SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ
                    7 Query     START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */
                    7 Query     SHOW VARIABLES LIKE 'gtid\_mode'
                    7 Query     SHOW MASTER STATUS
                    7 Query     UNLOCK TABLES
                    ......
                    7 Init DB   gs
                    7 Query     SHOW CREATE DATABASE IF NOT EXISTS `gs`
                    7 Query     SAVEPOINT sp
                   
                    7 Query     show create table `tb1`
                    7 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`
                   
                    7 Query     ROLLBACK TO SAVEPOINT sp
                    
                    7 Query     show create table `user`
                   7 Query     SELECT /*!40001 SQL_NO_CACHE */ * FROM `user`
                   
                    7 Query     ROLLBACK TO SAVEPOINT sp
                    7 Query     RELEASE SAVEPOINT sp
                    7 Quit

发现 --single-transaction 单独使用 与 --single-transaction 和 --master-data 结合使用 的区别如下图:

--single-transaction 和 --master-data 结合使用时,在导出开始,会短暂的持有一个全局的读锁,锁定时:刷新数据到磁盘、设置隔离级别为RR、开始事务、输出 binary log 的位置和文件名,然后解锁。这样就保证了:show master status 输出的 binary log 的位置和文件名 和 后面 导出的数据是同一个时间点的(同一个lsn),所以才能使用该备份 和 利用 change master to 构造一个 slave,成功的连接上 master.

可以看到这里使用了两次 flush tables:

FLUSH /*! 40101 LOCAL */ TABLES

FLUSH TABLES WITH READ LOCK

其原因是 第一次 flush 是不需要锁表的,第一次将所有数据刷新到磁盘之后,第二次 FLUSH TABLES WITH READ LOCK 时就会只有很少量的数据需要刷新到磁盘,所以第一次 flush 是为了尽量的 减少 第二次  fush 持有锁的时间

11. mysqldump 与 锁

1)--lock-tables 会在整个导出过程 lock read local 所有的表。该锁不会阻止其它session读和插入,但是显然阻塞了update。

2)--lock-all-tables 它请求发起一个全局的读锁,会阻止对所有表的写入操作(insert,update,delete),以此来确保数据的一致性。备份完成后,该会话断开,会自动解锁。

3)--single-transaction 和 --master-data 结合使用时,也是在开始时,会短暂的请求一个全局的读锁,会阻止对所有表的写入操作。

4)--single-transaction 单独使用,不会有任何锁。但是测试表明: 它也需要对备份的表持有 metadata lock 的共享锁

而我们知道,一般的事务,持有的是 行锁,还有 metadata lock 的共享锁。所以实际上,mysqldump不论你使用哪些选项,都不会阻塞事务的执行。

因为它们对锁的申请,没有任何排它性。而不像DDL一样需要持有 metadata lock 上的独占锁(排它锁)。当然DDL也会阻塞mysqldump。

mysqldump 一定需要表上的 metadata lock 共享锁。然后,要么需要所有备份表上的local读锁(lock table tb1 read local),要么需要的是所有备份表上的全局读锁(FLUSH TABLES WITH READ LOCK;),要么短暂持有全局锁。

12. mysqldump 与 Waiting for table flush

需要特别注意的是 mysqldump 很有可能导致 Waiting for table flush,比如 --single-transaction --master-data=2 一起用时,会执行 flush tables,而flush tables 可能会导致 Waiting for table flush !!!需要特别注意!!!!

所以最安全的mysqldump方式为

mysqldump -uroot -pxxxxx --single-transaction --databases testdb --where "1=1 limit 100000" > testdb_10W.sql

个人已经多次遇到这个问题。。。

参考:http://imysql.cn/2008_10_24_deep_into_mysqldump_options

 

posted on 2015-10-21 18:21  digdeep  阅读(25356)  评论(0编辑  收藏
不懂数据库和Web安全的架构师不是一个好的程序员。