Oracle Series Sixteen: Database Backup

1. Classification of database backup

1.1 Logical Backup and Physical Backup

Database backup is divided into logical backup and physical backup according to the backup status.

(1) Logical backup

Use SQL to extract data from the database and save it as a binary file for backup. The business database adopts this method and does not need to be in archive mode. For example, in Oracle, use EXPORT to export database objects (users, tables, stored procedures), and use IMPORT to import logical backup files into the database (Oracle exp/imp).

Advantages: You can back up only certain tables or certain data; you can perform cross-platform recovery between different versions; you can store and save space after compression.

Disadvantages: For large-scale databases, it takes a long time to execute statements; complete consistency cannot be guaranteed (for example, new data is inserted at the same time).

(2) Physical backup

Physical backup refers to directly copying all the content on the database storage medium, including the operating system level and the database engine level, so that the entire database can be completely restored. Generally requires an external storage device.

Pros: Fast and reliable; can provide consistent snapshots.

Disadvantages: It can only provide recovery to a "certain point in time", cannot selectively (by table or user) backup and restore, only full database backup and restore; cannot be used for cross-platform migration.

• Cold backup: occurs when the database has been shut down normally (offline state), and all data files are offline. During the backup process, the database cannot do other work, and the integrity and consistency of the data can be guaranteed.
• Hot backup: It is performed when the database is running (online), and will not affect normal business operations. It can be backed up at the table space or database file level, and it is transparent to users, and can maintain business continuity. The backup time is short, up to seconds Level recovery (recovery to a point in time). To put the log in the archive mode for hot backup, it is necessary to consider that the data being written or modified may cause data inconsistency, and take special measures to ensure data integrity.

(3) Archive mode and non-archive mode

• Archive mode : In archive mode, the database saves historical records to a set of special files called "archive logs". These logs contain details of previously committed transactions, making it possible to recover or restore lost or corrupted data. Due to the frequent writes to the log file, performance will be reduced.
• Non-archive mode : In non-archive mode, when a transaction is committed, its results are written directly to the main data file. Instead of additionally generating log files like the archive mode. Although this method can improve performance and reduce space overhead, there is also the risk that data cannot be fully recovered when data is lost or damaged.

1.2 Full Backup/Differential Backup/Incremental Backup

(1) Full backup (Full) : Back up all selected files, and does not rely on the file's archive attribute to determine which files to back up (each file is marked as backed up, eliminating the archive attribute).

(2) Differential backup (Differential) : Back up all files that have changed since the last full backup (do not mark them as backed up files after backup, and do not remove the archive attribute). (Backup takes a long time, takes up a lot of space, and restores quickly).

(3) Incremental backup (Incremental) : Back up all files that have changed since the last backup (no matter what kind of backup) (mark files after backup, eliminate archive attributes). (Short backup time, less space, slow recovery).

Combination example:

• Full + poor backup: Full backup is performed on Monday, and differential backup is performed from Tuesday to Friday. If the data is destroyed on Friday, you need to restore the full backup on Monday and the differential backup on Friday.
• Complete + additional backup: complete backup on Monday, and incremental backup of models from Tuesday to Friday. If the data is destroyed on Friday, you need to restore the full backup on Monday and the incremental backups from Tuesday to Friday.

2. Oracle logical backup

Oracle supports two types of logical backups: export/import utility and data pump.

2.1 EXP/IMP

(1) EXP export

• full mode

exp SYSTEM/MANAGER BUFFER=64000 file= C:\full.dmp full=Y

• user mode

exp detail12/detail12 owner=(detail12,detail11) file=/home/oracle/detail.dmp

exp detail12/detail12@RACDB_192.168.1.13 file=d:/detail.dmp

Among them, RACDB_192.168.1.13is the net service name of Oracle Net Configuration Assistant.

• table schema

exp detail12/detail12 owner=detail12 tables=(T_JBXX) file=/home/oracle/t_jbxx.dmp

If T_JBXX is a partition table, use tables=(T_JBXX1:P1，T_JBXX2:P2the format of ).

query field format:

query="""where dept_date<to_date('2014-02-01 00:00:10','yyyy-mm-dd hh24:mi:ss')"""

Note : do not import permissions and indexes can be joinedGRANTS=Y INDEXES=Y

keyword description

keywords	description (default)
USERID	username/password
FULL	Export entire file (N)
BUFFER	data buffer size
OWNER	List of owner usernames
FILE	Output file (EXPDAT.DMP)
TABLES	list of table names
COMPRESS	import into a zone (Y)
RECORDLENGTH	The length of the IO record
GRANTS	Export permission (Y)
INCTYPE	incremental export type
INDEXES	export index (Y)
RECORD	Track Incremental Export (Y)
DIRECT	direct path (N)
TRIGGERS	Export Trigger (Y)
LOG	log file for screen output
STATISTICS	Analysis object (ESTIMATE)
ROWS	Export Data Rows (Y)
PARFILE	parameter file name
CONSISTENT	Crosstab Consistency (N)
CONSTRAINTS	Exported Constraints (Y)
OBJECT_CONSISTENT	Transactions set to read-only only during object export (N)
FEEDBACK	show progress every x lines(0)
FILE SIZE	Maximum size of each dump file
FLASHBACK_SCN	The SCN used to set the session snapshot back to the previous state
FLASHBACK_TIME	The time used to get the SCN closest to the specified time
QUERY	select clause to export a subset of the table
RESUMABLE	Hang on encountering whitespace-related errors (N)
RESUMABLE_NAME	A text string identifying a recoverable statement
RESUMABLE_TIMEOUT	RESUMABLE wait time
TTS_FULL_CHECK	Perform a full or partial dependency check on TTS
TABLESPACES	list of tablespaces to export
TRANSPORT_TABLESPACE	export transportable tablespace metadata (N)
TEMPLATE	Call the template name exported by iAS mode

(2) IMP import

• full mode

imp SYSTEM/MANAGER BUFFER=64000 file=C:\full.dmp full=Y

• user mode

imp detail12/detail12 fromuser=(detail12，detail11) touser=(detail12，detail11) file=/home/oracle/detail.dmp

• table schema

imp detail12/detail12 owner=detail12 tables=(T_JBXX) file=/home/oracle/t_jbxx.dmp

Notice

• IMP imports must be specified Full=Y, or provided with fromuser/touserarguments, or provided with tablesarguments.
• The character set needs to be set as required before importingexport NLS_LANG=AMERICAN_AMERICA.ZHS16GBK
• 忽略创建表错误可加入IGNORE=Y，不导入权限和索引可加入 GRANTS=Y INDEXES=Y
• 导入时发生IMP-00032错误，表示SQL语句超过缓冲区长度，可以加入选项：buffer=100000000

关键字说明

关键字	说明 (默认值)
USERID	用户名/口令
FULL	导入整个文件 (N)
BUFFER	数据缓冲区大小
FROMUSER	所有者用户名列表
FILE	输入文件 (EXPDAT.DMP)
TOUSER	用户名列表
SHOW	只列出文件内容 (N)
TABLES	表名列表
IGNORE	忽略创建错误 (N)
RECORDLENGTH	IO 记录的长度
GRANTS	导入权限 (Y)
INCTYPE	增量导入类型
INDEXES	导入索引 (Y)
COMMIT	提交数组插入 (N)
ROWS	导入数据行 (Y)
PARFILE	参数文件名
LOG	屏幕输出的日志文件
CONSTRAINTS	导入限制 (Y)
DESTROY	覆盖表空间数据文件 (N)
INDEXFILE	将表/索引信息写入指定的文件
SKIP_UNUSABLE_INDEXES	跳过不可用索引的维护 (N)
FEEDBACK	每 x 行显示进度 (0)
TOID_NOVALIDATE	跳过指定类型 ID 的验证
FILESIZE	每个转储文件的最大大小
STATISTICS	始终导入预计算的统计信息
RESUMABLE	在遇到有关空间的错误时挂起 (N)
RESUMABLE_NAME	用来标识可恢复语句的文本字符串
RESUMABLE_TIMEOUT	RESUMABLE 的等待时间
COMPILE	编译过程， 程序包和函数 (Y)
STREAMS_CONFIGURATION	导入流的一般元数据 (Y)
STREAMS_INSTANTIATION	导入流实例化元数据 (N)

2.2 EXPDP/IMPDP

（1）数据泵介绍

Oracle Database 10g引入了最新的数据泵(Data Dump)技术，使DBA或开发人员可以将数据库元数据(对象定义)和数据快速移动到另一个oracle数据库中，与Export / Import相比，它提供更好的性能、安全性和灵活性。

• 并行处理： Oracle 数据泵支持并行处理（通过指定 PARALLEL 参数启用），这使得导入和导出任务更加快速和高效。
• 可定制： 数据泵允许用户选择要包含或排除的对象类型（如表、视图、约束等），以及要包含或排除的特定对象。
• 压缩： Oracle 数据泵支持压缩功能，可减少导出文件的大小，并提高传输速度。
• 安全性： 数据泵支持 SSL 加密协议来保护敏感信息，在安全方面非常有优势。
• 多平台兼容性： Oracle 数据泵支持多个平台上运行，例如 Windows 和 Linux 等操作系统。

（2）数据泵的使用

EXP和IMP是客户段工具程序，它们既可以在可以客户端使用，也可以在服务端使用。 EXPDP和IMPDP是服务端的工具程序，他们只能在ORACLE服务端使用，不能在客户端使用。

使用EXPDP工具时，其转储文件只能被存放在DIRECTORY对象对应的OS目录中,而不能直接指定转储文件所在的OS目录。因此，使用EXPDP工具时，必须首先建立DIRECTORY对象，并且需要为数据库用户授予使用DIRECTORY对象权限。

使用Data Pump，可将整个数据库或特定模式及其对象（如表格、索引、约束和其数据）导出/导入，还可指定选项，例如表空间、压缩级别、加密和远程导出/导入的网络链接。

Data Pump包括两个客户端实用程序：expdp（Export Data Pump）和impdp（Import Data Pump）。

e.g.

create directory imp_dir as 'D:\imp_dir';
GRANT READ, WIRTE ON DIRECTORY imp_dir TO detail;

expdp scott/tiger DUMPFILE=tmp_dump.dmp  DIRECTORY= imp_dir

impdp scott/tiger DUMPFILE=tmp_dump.dmp  DIRECTORY= imp_dir