本文源自：https://www.cnblogs.com/digdeep/p/4898622.html

mysqldump 是MySQL的一個命令行工具，用于邏輯備份?？梢詫?shù)據(jù)庫和表的結(jié)構(gòu)，以及表中的數(shù)據(jù)分別導(dǎo)出成：create database, create table, insert into的sql語句。當(dāng)然也可以導(dǎo)出 存儲過程，觸發(fā)器，函數(shù)，調(diào)度事件(events)。不管是程序員，還是DBA都會經(jīng)常使用的一個工具。

1. mysqldump --help

mysqldump 的選項很多，我們看一下他的幫助文檔：

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 --databaseswith 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 'STARTSLAVE' 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. Bydefault tables are dumped in a format optimized forMySQL. Legal modes are: ansi, mysql323, mysql40,postgresql, oracle, mssql, db2, maxdb, no_key_options,no_table_options, no_field_options. One can use severalmodes separated by commas. Note: Requires MySQL serverversion 4.1.0 or higher. This option is ignored withearlier server versions.--compact Give less verbose output (useful for debugging). Disablesstructure comments and header/footer constructs. Enablesoptions --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; inthis case no tables are given. All name arguments areregarded as database names. 'USE db_name;' will beincluded 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 automaticallyenables --master-data.-K, --disable-keys '/*!40000 ALTER TABLE tb_name DISABLE KEYS */; and'/*!40000 ALTER TABLE tb_name ENABLE KEYS */; will be putin the output.(Defaults to on; use --skip-disable-keys to disable.)--dump-slave[=#] This causes the binary log position and filename of themaster to be appended to the dumped data output. Settingthe value to 1, will printit as a CHANGE MASTER commandin the dumped data output; if equal to 2, that commandwill be prefixed with a comment symbol. This option willturn --lock-all-tables on, unless --single-transaction isspecified too (in which case a global read lock is onlytaken a short time at the beginning of the dump - don'tforget to read about --single-transaction below). In allcases any action on logs will happen at the exact momentof the dump.Option automatically turns --lock-tables off.-E, --events Dump events.-e, --extended-insert Use multiple-row INSERT syntax that include severalVALUES lists.(Defaults to on; use --skip-extended-insert to disable.)--fields-terminated-by=name Fields in the output file are terminated by the givenstring.--fields-enclosed-by=name Fields in the output file are enclosed by the givencharacter.--fields-optionally-enclosed-by=name Fields in the output file are optionally enclosed by thegiven character.--fields-escaped-by=name Fields in the output file are escaped by the givencharacter.-F, --flush-logs Flush logs file in server before starting dump. Note thatif you dump many databases at once (using the option--databases= or --all-databases), the logs will beflushed for each database dumped. The exception is whenusing --lock-all-tables or --master-data: in this casethe logs will be flushed only once, corresponding to themoment all tables are locked. So if you want your dumpand the log flush to happen at the same exact moment youshould use --lock-all-tables or --master-data with--flush-logs.--flush-privileges Emit a FLUSH PRIVILEGES statement after dumping the mysqldatabase. This option should be used any time the dumpcontains the mysql database and any other database thatdepends on the data in the mysql database for properrestore. -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) inhexadecimal format.-h, --host=name Connect to host.--ignore-table=name Do not dump the specified table. To specify more than onetable to ignore, use the directive multiple times, oncefor each table. Each table must be specified with bothdatabase and table names, e.g.,--ignore-table=database.table.--include-master-host-port Adds 'MASTER_HOST=<host>, MASTER_PORT=<port>' to 'CHANGEMASTER 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 givenstring.-x, --lock-all-tables Locks all tables across all databases. This is achievedby taking a global read lock for the duration of thewhole 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 beappended to the output. If equal to 1, will print it as aCHANGE MASTER command; if equal to 2, that command willbe prefixed with a comment symbol. This option will turn--lock-all-tables on, unless --single-transaction isspecified too (in which case a global read lock is onlytaken a short time at the beginning of the dump; don'tforget to read about --single-transaction below). In allcases, any action on logs will happen at the exact momentof the dump. Option automatically turns --lock-tablesoff.--max-allowed-packet=# The maximum packet length to send to or receive fromserver.--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 thatnormally 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 uniquekey, if such a key exists. Useful when dumping a MyISAMtable to be loaded into an InnoDB table, but will makethe dump itself take considerably longer.-p, --password[=name] Password to use when connecting to server. If password isnot 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 usedin systems (e.g., DOS, Windows) that use carriage-returnlinefeed pairs (\r\n) to separate text lines. This optionensures 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. Possiblevalues for this option are ON, OFF and AUTO. If ON isused and GTIDs are not enabled on the server, an error isgenerated. If OFF is used, this option does nothing. IfAUTO is used and GTIDs are enabled on the server, 'SET@@GLOBAL.GTID_PURGED' is added to the output. If GTIDsare disabled, AUTO does nothing. If no value is suppliedthen the default (AUTO) value will be considered.--single-transaction Creates a consistent snapshot by dumping all tables in asingle transaction. Works ONLY for tables stored instorage engines which support multiversioning (currentlyonly InnoDB does); the dump is NOT guaranteed to beconsistent for other storage engines. While a--single-transaction dump is in process, to ensure avalid dump file (correct table contents and binary logposition), no other connection should use the followingstatements: ALTER TABLE, DROP TABLE, RENAME TABLE,TRUNCATE TABLE, as consistent snapshot is not isolatedfrom 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 withother 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 againsthostname used when connecting. This option is disabled bydefault.-T, --tab=name Create tab-separated textfile for each table to givenpath. (Create .sql and .txt files.) NOTE: This only worksif mysqldump is run on the same machine as the mysqldserver.--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 ofTIMESTAMP data when a server has data in different timezones or data is being moved between servers withdifferent 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)

總體看來，幫助文檔分成了兩個部分。前一個部分是對各種選項的說明，后一個部分是mysqldump的各種選項的默認(rèn)值。

mysqldump擁有超多的選項，這樣說明它很靈活，功能強大。為了好理解，可以將他的眾多的選項和參數(shù)，根據(jù)他們的功能分為幾個類別來介紹。

在此之前，我們還要搞清楚mysqldump的所有的默認(rèn)選項的值，它們的含義。

2. mysqldump 默認(rèn)選項：

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)

這些默認(rèn)值，有的是 false, 有的是 true，有的沒有默認(rèn)值。

我們要關(guān)注的是 默認(rèn)為 true，也就是 mysqldump 默認(rèn)給我打開的選擇，它們的具體含義如下：

add-drop-table TRUE 表示在生成表結(jié)構(gòu)語句之前，生成對應(yīng)的 DROP TABLE IF EXISTS `table_name`; 語句 add-locks TRUE 表示在生成表中數(shù)據(jù)的 insert into `table_name` values(...) 之前生成 LOCK TABLES `tab` WRITE;語句 comments TRUE 表示生成備注，就是所有 -- 開頭的說明，比如：-- Dumping data for for table `tab`. 最好還是啟用； create-options TRUE 表示在生成表結(jié)構(gòu)時會生成：ENGINE=InnoDB AUTO_INCREMENT=827 DEFAULT CHARSET=utf8; 附加建表選項 default-character-set utf8 指定語句：/*!40101 SET NAMES utf8 */;中的字符集；可能你需要改成 --default-character-set=utf8mb4 disable-keys TRUE 表示生產(chǎn) insert 語句之前，生成：/*!40000 ALTER TABLE `tbl` DISABLE KEYS */; 可以加快insert速度； extended-insert TRUE 表示生產(chǎn)的insert是insert into `tbl` values(...),(...),數(shù)據(jù)行按照net-buffer-length分割合并成多個batch insert lock-tables TRUE 表示在導(dǎo)出的過程中會鎖定所有表； max-allowed-packet 25165824 最大支持 24M 的數(shù)據(jù)包； net-buffer-length 1046528 1M大小的socket buffer quick TRUE 表示在導(dǎo)出語句時，不緩存，直接輸出到控制臺或者文件中； quote-names TRUE 表示對表名和列名使用 `` 符號包裹；防止它們是關(guān)鍵字時會出錯; 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 表示是否在導(dǎo)出文件的末尾生成導(dǎo)出時間：-- Dump completed on 2015-09-15 11:15:10 secure-auth TRUE 表示登錄判斷密碼時使用新的加密算法，拒絕就的加密算法 triggers TRUE 表示生成觸發(fā)器腳本； tz-utc TRUE 表示是否生成：/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */; /*!40103 SET TIME_ZONE='+00:00' */;

如果要關(guān)閉這些打開的默認(rèn)選項時，需要明確指定：mysqldump -uxxx -p aazj?--extended-insert=0?Users > Users.sql; =0 表示關(guān)閉選項。

上面這些默認(rèn)選項，最好結(jié)合一個例子來理解：

-- 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

2. mysqldump 登錄服務(wù)器的相關(guān)選項

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和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 作為一個客戶端工具，它會去上述目錄中尋找 my.cnf 文件，然后讀取該文件中?[mysqldump] 和 [client]?下面的選項；

2）那些 defaults 相關(guān)的選項都是為了另外指定 配置文件和登錄文件，極少使用；

? -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）這幾個選項指定 登錄的用戶名，密碼，mysqld IP地址，端口，連接使用的協(xié)議等等。

??? 一般常用的是 -h192.168.2.xx -uxxx -p ，如果mysqld默認(rèn)端口不是3306，則需要使用 -Pxxx 指定端口.

??? --max-allowed-packet 我們一般配置在my.cnf中。--net-buffer-length 是為了優(yōu)化網(wǎng)絡(luò)連接的socket buffer.

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

3. mysqldump 選擇備份內(nèi)容的相關(guān)選項

我們可以選擇備份所有數(shù)據(jù)庫，某幾個數(shù)據(jù)庫，某一個數(shù)據(jù)庫，某一個數(shù)據(jù)庫中的某幾個表，某一個數(shù)據(jù)庫中的一個表；

可以選擇是否備份 存儲過程和函數(shù)，觸發(fā)器，調(diào)度事件.

1）選擇導(dǎo)出的數(shù)據(jù)庫 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]?? 導(dǎo)出數(shù)據(jù)庫?database 中的表結(jié)構(gòu) 和 表中數(shù)據(jù)；

2）選擇是否導(dǎo)出 建庫，建表語句，是否導(dǎo)出 表中的數(shù)據(jù)：

-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. (不導(dǎo)出建庫語句: CREATE DATABASE，也就是不導(dǎo)庫結(jié)構(gòu))

-t,?--no-create-info?Don't write table creation info. (不導(dǎo)出建表語句)

-d,?--no-data???????? No row information. (不導(dǎo)出數(shù)據(jù)，有時我們僅僅需要導(dǎo)出表結(jié)構(gòu)，也就是建表語句就行了)

3）選擇是否導(dǎo)出 存儲過程和函數(shù)，觸發(fā)器，調(diào)度事件：

-R, --routines????? Dump stored routines (functions and procedures). (導(dǎo)出存儲過程和函數(shù))

--triggers??????????? Dump triggers for each dumped table. (Defaults to on; use --skip-triggers to disable.) (導(dǎo)出觸發(fā)器)

--skip-triggers???? 不導(dǎo)出觸發(fā)器

-E, --events??????? Dump events. 導(dǎo)出調(diào)度事件(根據(jù)備份的目的進(jìn)行選擇，如果是搭建slave，那么就不要導(dǎo)出events.)

4）指定不導(dǎo)出 某個庫的某個表：

--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. (在導(dǎo)出數(shù)據(jù)庫時，排除某個或者某幾個表不導(dǎo)出)

5) 按照 where 條件導(dǎo)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> 導(dǎo)出單表的結(jié)構(gòu)和數(shù)據(jù)：mysqldump -uxxx -p db1 tb1 > tb1.sql; 導(dǎo)出數(shù)據(jù)庫 db1 中的 表 tb1 的表結(jié)構(gòu) 和 表中數(shù)據(jù)；

2> 導(dǎo)出多表的結(jié)構(gòu)和數(shù)據(jù)：mysqldump -uxxx -p db1 tb1 tb2 > tb1_tb2.sql; 導(dǎo)出數(shù)據(jù)庫 db1 中的 表 tb1、tb2 的表結(jié)構(gòu) 和 表中數(shù)據(jù)；

3> 導(dǎo)出單表的結(jié)構(gòu)：mysqldump -uxxx -p?--no-data?db1 tb1 > tb1.sql; 導(dǎo)出數(shù)據(jù)庫 db1 中的 表 tb1 的表結(jié)構(gòu); 其實也可以使用: show create table tb1

4> 我們無法使用 mysqldump 到達(dá) 只導(dǎo)出某個或某幾個表的數(shù)據(jù)，而不導(dǎo)出建表語句的目的。

???? 但是我們可以使用 select * from table into outfile 'file.sql', 比如：select * from Users into outfile '/tmp/Users.sql';?注意需要對目錄的寫權(quán)限。

5> 導(dǎo)出單個庫中庫結(jié)構(gòu)、表結(jié)構(gòu)、表數(shù)據(jù)：mysqldump -uxxx -p?--databases?db1 > db1.sql

6> 導(dǎo)出多個庫中庫結(jié)構(gòu)、表結(jié)構(gòu)、表數(shù)據(jù)：mysqldump -uxxx -p?--databases?db1 db2 > db1_db2.sql

7> 導(dǎo)出單個庫中庫結(jié)構(gòu)、表結(jié)構(gòu)、不要表數(shù)據(jù)：mysqldump -uxxx -p?--no-data?--databases db1 > db1.sql

8> 導(dǎo)出單個庫中數(shù)據(jù)，不要庫結(jié)構(gòu)和表結(jié)構(gòu)：mysqldump -uxxx -p?--no-create-db --no-create-info --databases?db1 > db1.sql

9> 導(dǎo)出多個庫中庫結(jié)構(gòu)、表結(jié)構(gòu)、不要表數(shù)據(jù)：mysqldump -uxxx -p?--no-data?--databases?db1 db2 > db1_db2.sql

10> 導(dǎo)出數(shù)據(jù)庫中所有 庫 的庫結(jié)構(gòu)，表結(jié)構(gòu)，數(shù)據(jù)：mysqldump -uxxx -p?--all-databases?> all.sql

11> 導(dǎo)出數(shù)據(jù)庫中所有 庫 的庫結(jié)構(gòu)，表結(jié)構(gòu)，不要數(shù)據(jù)：mysqldump -uxxx -p --all-databases?--no-data?> all.sql

12> 導(dǎo)出單個庫中庫結(jié)構(gòu)、表結(jié)構(gòu)、表數(shù)據(jù)，排除某個表：mysqldump -uxxx -p?--databases db1?--ignore-table=db1.test?> db1.sql

4. mysqldump 事務(wù) 和 數(shù)據(jù)一致性(鎖) 的相關(guān)選項

在使用mysqldump邏輯備份時，事務(wù)和數(shù)據(jù)一致性的選項時至關(guān)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 可以得到一致性的導(dǎo)出結(jié)果。它是通過將導(dǎo)出行為放入一個事務(wù)中來實現(xiàn)的。

???? 它有一些要求：只能是 innodb 引擎；導(dǎo)出的過程中，不能有任何人執(zhí)行 alter table, drop table, rename table, truncate table等DDL語句。

???? 實際上DDL會被事務(wù)所阻塞，因為事務(wù)持有表的metadata lock 的共享鎖，而DDL會申請metadata lock的互斥鎖，所以阻塞了。

?????--single-transaction 會自動關(guān)閉 --lock-tables 選項；上面我們說到mysqldump默認(rèn)會打開了--lock-tables，它會在導(dǎo)出過程中鎖定所有表。

??? 因為 --single-transaction 會自動關(guān)閉--lock-tables，所以單獨使用--single-transaction是不會使用鎖的。與 --master-data 合用才有鎖。

2）--lock-tables

???? 該選項默認(rèn)打開的，上面已經(jīng)說到了。它的作用是在導(dǎo)出過程中鎖定所有表。--single-transaction 和?--lock-all-tables 都會將該選項關(guān)閉。

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. 啟用該選項，會自動關(guān)閉 --single-transaction 和 --lock-tables.

上面三個選項中，只有 --lock-tables 默認(rèn)是打開的；打開 --single-transaction 或者 打開 --lock-all-tables 都將關(guān)閉 --lock-tables. 而--lock-all-tables會自動關(guān)閉 --single-transaction 和 --lock-tables。所以三者是互斥的。我們應(yīng)該一次只啟用其中一個選項。

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.

?????? 為了獲得導(dǎo)出數(shù)據(jù)和刷新日志的一致性(同時發(fā)生)，必須將 --flush-logs 選項和 --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.

??????如何導(dǎo)出包含了mysql數(shù)據(jù)，就應(yīng)該啟用該選項。該選項會在導(dǎo)出的 mysql 數(shù)據(jù)庫的后面加上 flush privileges 語句，因為在向mysql數(shù)據(jù)庫inert了語句

????? 之后，必須使用 flush privileges，不然權(quán)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.

所以為了獲得一致性的備份數(shù)據(jù)和在備份是同時刷新binary日志，我們應(yīng)該如下結(jié)合使用這些選項(完美組合——其實并不完美！！！因為：a global read lock is only taken a short time at the beginning of the dump，會導(dǎo)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 不是必須的; 搭建slave時，不要導(dǎo)出events，但是需要導(dǎo)出rountines.)

其中被?--master-data 打開的 --lock-all-tables 選項，又被 --single-transaction 關(guān)閉掉了。--flush-logs 借助于 --master-data 可以達(dá)到即使一次導(dǎo)出多個數(shù)據(jù)庫時，其 flush 的二進(jìn)制日志也是在同一個時間點的，不是每一個數(shù)據(jù)庫flush一次的。并且這個時間點 和 --master-data 記錄的 binary log position 和 binary log file是同一個時間點，這些都是利用了 --single-transaction 和?--master-data?合用時短暫的使用一個全局的讀鎖來達(dá)到目的的。

5. mysqldump 復(fù)制 的相關(guān)選項

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.

?????? 該選項，上面已經(jīng)介紹了。--master-data=1 表示會導(dǎo)出 change master to 語句，--master-data=2 該語句放在注釋中，默認(rèn)是為 0 。

?????? 一般會和 --single-transaction一起使用，用于搭建master-slave環(huán)境。

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

在導(dǎo)出文件的前30行左右可以看到 change master to 語句?？梢允褂?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 幾乎一樣。區(qū)別只是--dump-slave用于slave建立下一級的slave；而 --master-data用于master建立slave;

??????如果在 master 上使用 --dump-slave 會報錯：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 導(dǎo)出 stop slave 語句, 在 change master 之后導(dǎo)出 start slave語句。其實是一個自動化的處理。和 --master-data=1 類似。

如下圖所示：開頭有 stop slave, 結(jié)尾有 start slave語句：

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

????? 該選擇要結(jié)合 --dump-slave=1/2 使用。會在導(dǎo)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.

???? 該選擇要結(jié)合 --dump-slave=1/2 使用。會在導(dǎo)出中加入mysql的 port。

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

???? 在備份之后，刪除 master上的binary log。該選項會自動打開 --master-data 選項(等于2)。該選項一般不用。日志一般不能隨便刪除。

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.

???? 該選項用于啟用了GTID特性的環(huán)境。

6. mysqldump 字符集 的相關(guān)選項

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 開啟和關(guān)閉。也可以使用 --skip-set-charset 關(guān)閉。

?? 該選項我們上面已經(jīng)說到了。表示是否生成?/*!40101 SET NAMES utf8 */;

2）-N, --no-set-names?

???? Same as --skip-set-charset. 關(guān)閉 --set-charset. 不生成?/*!40101 SET NAMES utf8 */;?語句。

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

???? 該選項上面也涉及到了。指定語句：/*!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 語句 的相關(guān)選項

? --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 導(dǎo)出格式?的相關(guān)選項

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.

???? 導(dǎo)出sql語句的兼容格式。如果我們需要從MySQL導(dǎo)出，然后導(dǎo)入到其它數(shù)據(jù)庫，則可使用該選項。--compatible=oracle/postgresql/mssql

2）-Q, --quote-names??

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

???? 將表名和列名使用 ``包裹。以防他們是關(guān)鍵字時報錯。

9. mysqldump 錯誤處理的相關(guān)選項

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

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

10. mysqldump 實現(xiàn)原理

為了探求 mysqldump 的備份是如何實現(xiàn)的，我們需要在 my.cnf 中的[mysqld] 參數(shù)段加入：

general_log=on general_log_file=general.log

這樣我們就可以通過觀察 general.log 的輸出，來了解 mysqldump 的備份是如何實現(xiàn)的。

1）--lock-tables 是如何實現(xiàn)的：

先執(zhí)行：mysqldump -uroot -p --databases gs --lock-tables > gs_l.sql， 然后查看 general.log:

3 Init DB gs3 Query SHOW CREATE DATABASE IF NOT EXISTS `gs`3 Query show tables3 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=13 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_database3 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=13 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_database3 Query SHOW TRIGGERS LIKE 'user'3 Query SET SESSION character_set_results = 'utf8'3 Query UNLOCK TABLES3 Quit

1> 第一步： SHOW CREATE DATABASE?IF NOT?EXISTS?`gs`; 導(dǎo)出了建庫語句；

2> 第二步：show tables; 獲得數(shù)據(jù)庫中所有表名，然后鎖住：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;?語句

3> 第三步：show create table?'tb1'; 導(dǎo)出了 tb1 的建表語句；

4> 第四步：show fields from `tb1`;?SELECT /*!40001 SQL_NO_CACHE */ *?FROM `tb1`; 導(dǎo)出了表中的數(shù)據(jù)；

......

5> 最后導(dǎo)出了 trigger, 最后的最后 unlock tables; 結(jié)束。

可以看到 --lock-tables 在導(dǎo)出一個數(shù)據(jù)庫時，會在整個導(dǎo)出過程 lock read local 所有的表。該鎖不會阻止其它session讀和插入。

2）--lock-all-tables 的實現(xiàn)：

先執(zhí)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 on4 Query /*!40100 SET @@SQL_MODE='' */4 Query /*!40103 SET TIME_ZONE='+00:00' */4 Query FLUSH TABLES4 Query FLUSH TABLES WITH READ LOCK4 Query SHOW VARIABLES LIKE 'gtid\_mode'... ...4 Init DB gs4 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_database4 Query SHOW TRIGGERS LIKE 'user'4 Query SET SESSION character_set_results = 'utf8'4 Quit

它的實現(xiàn)使用了?FLUSH TABLES;?FLUSH TABLES WITH?READ?LOCK;?語句。在最后沒有看到解鎖語句。

它請求發(fā)起一個全局的讀鎖，會阻止對所有表的寫入操作，以此來確保數(shù)據(jù)的一致性。備份完成后，該會話斷開，會自動解鎖。

3）--single-transaction 的實現(xiàn)：

先執(zhí)行：?mysqldump -uroot -p --databases gs --single-transaction > gs_l.sql，在查看 general.log:

151022 14:41:34 5 Connect root@localhost on5 Query /*!40100 SET @@SQL_MODE='' */5 Query /*!40103 SET TIME_ZONE='+00:00' */5 Query SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ5 Query START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */5 Query SHOW VARIABLES LIKE 'gtid\_mode'5 Query UNLOCK TABLES... ...5 Init DB gs5 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 sp5 Query RELEASE SAVEPOINT sp5 Quit

基本過程是：

1> 先改變事務(wù)隔離級別：SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE?READ

2> 開始事務(wù)：START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */

3> unlock tables;

4> 導(dǎo)出建庫語句； SHOW CREATE DATABASE?IF NOT?EXISTS?`gs`

5> 打開一個 savepoint:?SAVEPOINT sp;

6> 導(dǎo)出 表 tb1 的結(jié)構(gòu)和數(shù)據(jù)；

7>?ROLLBACK TO SAVEPOINT sp; 回滾到savepoint;

對其它表重復(fù)該過程；

8> 最后 realease savepoint p; 釋放savepoint;

整個過程，沒有任何鎖。RR隔離級別保證在事務(wù)中只讀取本事務(wù)之前的一致性的數(shù)據(jù)。 rollback to savepoint sp; 保證了對數(shù)據(jù)庫中的數(shù)據(jù)沒有影響。

4）--master-data 的實現(xiàn)：

先執(zhí)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 on6 Query /*!40100 SET @@SQL_MODE='' */6 Query /*!40103 SET TIME_ZONE='+00:00' */6 Query FLUSH /*!40101 LOCAL */ TABLES6 Query FLUSH TABLES WITH READ LOCK6 Query SHOW VARIABLES LIKE 'gtid\_mode'6 Query SHOW MASTER STATUS

發(fā)現(xiàn)了 --lock-all-tables一樣，就多了一句：show master status;

5）--single-transaction 和 --master-data 結(jié)合使用：

先執(zhí)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 on7 Query /*!40100 SET @@SQL_MODE='' */7 Query /*!40103 SET TIME_ZONE='+00:00' */7 Query FLUSH /*!40101 LOCAL */ TABLES7 Query FLUSH TABLES WITH READ LOCK7 Query SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ7 Query START TRANSACTION /*!40100 WITH CONSISTENT SNAPSHOT */7 Query SHOW VARIABLES LIKE 'gtid\_mode'7 Query SHOW MASTER STATUS7 Query UNLOCK TABLES......7 Init DB gs7 Query SHOW CREATE DATABASE IF NOT EXISTS `gs`7 Query SAVEPOINT sp7 Query show create table `tb1`7 Query SELECT /*!40001 SQL_NO_CACHE */ * FROM `tb1`7 Query ROLLBACK TO SAVEPOINT sp7 Query show create table `user`7 Query SELECT /*!40001 SQL_NO_CACHE */ * FROM `user`7 Query ROLLBACK TO SAVEPOINT sp7 Query RELEASE SAVEPOINT sp7 Quit

發(fā)現(xiàn) --single-transaction 單獨使用 與 --single-transaction 和 --master-data 結(jié)合使用 的區(qū)別如下圖：

--single-transaction 和 --master-data 結(jié)合使用時，在導(dǎo)出開始，會短暫的持有一個全局的讀鎖，鎖定時：刷新數(shù)據(jù)到磁盤、設(shè)置隔離級別為RR、開始事務(wù)、輸出 binary log 的位置和文件名，然后解鎖。這樣就保證了：show master status 輸出的 binary log 的位置和文件名 和 后面 導(dǎo)出的數(shù)據(jù)是同一個時間點的(同一個lsn)，所以才能使用該備份 和 利用 change master to 構(gòu)造一個 slave，成功的連接上 master.

可以看到這里使用了兩次 flush tables:

FLUSH /*! 40101 LOCAL */ TABLES

FLUSH TABLES WITH READ LOCK

其原因是 第一次 flush 是不需要鎖表的，第一次將所有數(shù)據(jù)刷新到磁盤之后，第二次 FLUSH TABLES WITH READ LOCK 時就會只有很少量的數(shù)據(jù)需要刷新到磁盤，所以第一次 flush 是為了盡量的 減少 第二次? fush 持有鎖的時間。

11. mysqldump 與 鎖

1）--lock-tables?會在整個導(dǎo)出過程 lock read local 所有的表。該鎖不會阻止其它session讀和插入，但是顯然阻塞了update。

2）--lock-all-tables?它請求發(fā)起一個全局的讀鎖，會阻止對所有表的寫入操作(insert,update,delete)，以此來確保數(shù)據(jù)的一致性。備份完成后，該會話斷開，會自動解鎖。

3）--single-transaction 和 --master-data?結(jié)合使用時，也是在開始時，會短暫的請求一個全局的讀鎖，會阻止對所有表的寫入操作。

4）--single-transaction?單獨使用，不會有任何鎖。但是測試表明:?它也需要對備份的表持有 metadata lock 的共享鎖。

而我們知道，一般的事務(wù)，持有的是 行鎖，還有 metadata lock 的共享鎖。所以實際上，mysqldump不論你使用哪些選項，都不會阻塞事務(wù)的執(zhí)行。

因為它們對鎖的申請，沒有任何排它性。而不像DDL一樣需要持有 metadata lock 上的獨占鎖(排它鎖)。當(dāng)然DDL也會阻塞mysqldump。

mysqldump?一定需要表上的 metadata lock 共享鎖。然后，要么需要所有備份表上的local讀鎖(lock table tb1?read local)，要么需要的是所有備份表上的全局讀鎖(FLUSH TABLES WITH?READ?LOCK;)，要么短暫持有全局鎖。

12. mysqldump 與?Waiting for table flush

需要特別注意的是 mysqldump 很有可能導(dǎo)致 Waiting for table flush，比如 --single-transaction --master-data=2 一起用時，會執(zhí)行 flush tables，而flush tables 可能會導(dǎo)致 Waiting for table flush ！！！需要特別注意！！！！

所以最安全的mysqldump方式為：

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

個人已經(jīng)多次遇到這個問題。。。

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

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