[MySQL] mysqldump 이용해서 백업하기

명령어 옵션들

mysqldump의 명령어 옵션는 아래와 같다.

$ mysqldump --help
mysqldump  Ver 10.13 Distrib 5.7.32, for osx10.15 (x86_64)
Copyright (c) 2000, 2020, 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/Cellar/mysql-client@5.7/5.7.32/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       This is a non-debug version. Catch this and exit.
  --debug-info        This is a non-debug version. Catch this and exit.
  --default-character-set=name
                      Set the default character set.
  --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-error=name A comma-separated list of error numbers to be ignored if
                      encountered during dump.
  --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. Deprecated. Always TRUE
  --ssl-mode=name     SSL connection mode.
  --ssl               Deprecated. Use --ssl-mode instead.
                      (Defaults to on; use --skip-ssl to disable.)
  --ssl-verify-server-cert
                      Deprecated. Use --ssl-mode=VERIFY_IDENTITY instead.
  --ssl-ca=name       CA file in PEM format.
  --ssl-capath=name   CA directory.
  --ssl-cert=name     X509 cert in PEM format.
  --ssl-cipher=name   SSL cipher to use.
  --ssl-key=name      X509 key in PEM format.
  --ssl-crl=name      Certificate revocation list.
  --ssl-crlpath=name  Certificate revocation list path.
  --tls-version=name  TLS version to use, permitted values are: TLSv1, TLSv1.1,
                      TLSv1.2
  --server-public-key-path=name
                      File path to the server public RSA key in PEM format.
  --get-server-public-key
                      Get server public key
  -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.
  --enable-cleartext-plugin
                      Enable/disable the clear text authentication plugin.

Variables (--variable-name=value)
and boolean options {FALSE|TRUE}  Value (after reading options)

모든 DB를 덤프하는 것보단...

mysqldump [DB_name [table_names [...]] [<options>[, ...]] 와 같이 DB 이름을 지정하여 사용하는 것이 좋다.

모든 DB를 --all-databases 인자와 함께 덤프를 하고 싶겠지만, mysql, information_schema 와 같은 시스템 데이터베이스까지 덤프를 하므로 추천하지 않는다.

그렇다면, 시스템 메타정보를 제외해보자

SELECT schema_name
   FROM information_schema.schemata
   WHERE schema_name NOT IN
        ('information_schema', 'mysql', 'performance_schema', 'sys' );

으로 받아온 나머지 DB이름을 for문으로 덤프하는 것을 추천한다.

결과는 아래와 같다.

mysql> SELECT schema_name  FROM information_schema.schemata where schema_name not in ('information_schema', 'mysql', 'performance_schema', 'sys' );
+-------------+
| schema_name |
+-------------+
| test        |
| tpcc        |
+-------------+
2 rows in set (0.00 sec)

쉘 스크립트로 백업받기

그렇다면, 쉘에서 받아올 수 있도록 해보자. (아래 mysql의 -N 옵션은 컬럼 이름을 출력하지 않는 옵션이며, --skip-column-names와 같다)

$ mysql -N -uroot <<< "SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('information_schema', 'mysql', 'performance_schema', 'sys' );"
test
tpcc

위의 명령어를 이용하여 출력해보자.

for i in `mysql --skip-column-names -uroot <<< "SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('information_schema', 'mysql', 'performance_schema', 'sys' );"`;
do
  echo "mysqldump $i -uroot > backup_$i.sql" ;
done;

위의 결과물은 아래와 같다.

$ for i in `mysql --skip-column-names -uroot <<< "SELECT schema_name FROM information_schema.schemata WHERE schema_name NOT IN ('information_schema', 'mysql', 'performance_schema', 'sys' );"`;
> do
>   echo "mysqldump $i -uroot > backup_$i.sql" ;
> done;
mysqldump test -uroot > backup_test.sql
mysqldump tpcc -uroot > backup_tpcc.sql
$

저장 프로시저, 함수도 포함해서 백업하고 싶다면?

--routines 옵션을 이용하면 된다.

mysqldump DB_name -uroot --routines > bck.sql

스키마만 백업하고 싶다면?

--no-data 옵션을 사용하면 된다.

mysqldump DB_name -uroot DB --no-data >  bck_scheme_only.sql

실제로는 ...

blob 컬럼은 잘 구슬려야 한다.

mysqldump 명령어를 쓸땐, --hex-blob 옵션을 무조건 넣어주어야 한다. 이 옵션이 있으면 blob 컬럼의 내용이 hex형태의 문자열로 변환되어 출력된다.

 

운용하고 있는 DB의 특정 테이블에 blob 필드가 있다면, EOF 문자로 인해 덤프파일이 중간에 끊기게 되며, 데이터를 유실하게 된다.
여태 백업받았던 파일이 깨진 백업일 것이다. 이 백업파일을 이용하여 복구를 할 수 없는 절망적인 상황이 닥친다.(

상상만으로도 끔찍하다

)

 

따라서, 이를 방지하기 위해 --hex-blob 옵션을 항상 써야 한다. mysqldump가 기입된 모든 스크립트에 항상 같이 기입한다. 설령 백업대상 DB에서 blob을 사용하는 테이블이 없다고 해도, 항상 기입하라. (blob이 있는 테이블이 언제라도 생성될 수 있다)

패킷사이즈 고려하기

또한, varchar가 많거나, blob, text 컬럼 등이 있다면 dump가 제대로 동작하지 않을 가능성이 크다. 왜냐하면, 소켓을 통해 백업을 건네주는데, 허용된 패킷사이즈가 레코드 혹은 테이블 사이즈에 비해 작기 때문이다. 따라서 --max_allowed_packet=<size> 을 이용하여 백업을 해야한다. (이는 my.cnf 파일에 지정하여 명령어 옵션을 생략할 수 있으나 추천하지 않는다.

 

아래는 내가 실제로 회사에서 사용하고 있는 백업 스크립트의 일부분이다.

# ... 생략 ...

mysqldump ${MYSQL_DB} \
          -u${MYSQL_USER} -p${MYSQL_PASS} \
          --max_allowed_packet=512M \
          --opt --quote-names --skip-set-charset \
          --hex-blob --default-character-set=utf8 \
          > $DBFILE_PATH

# ... 생략 ...

--opt, --quote-names, --default-character-set=utf8 에 관한 내용은 위애서 찾아보길 바란다.
(이중 --opt와 --quote-names 는 기본값으로 되어 있다.)