EXPDPIMPDP中的并⾏度PARALLEL参数
如果设置 EXPDP parallel=4 必须要设置4个EXPDP⽂件，不然PARALLEL是有问题的，同时EXPDP会使⽤⼀个WORKER进程导出METADATA，其他WORKER进程会同时出数据，如果EXPDP作业很于250M 只会启动⼀个WORKER进程如果是500M会启动2个，1000M 及会启动4个WOKER进程，⼀般来说加上%U来设置多个⽂件。
⽽IMPDP有所不同，会先启动⼀个WOKER进程METADATA导⼊，然后启动多个WORKER进程导⼊，所以再前期只会看到WOKER在导⼊METADATA，⽽且IMPDP如果PARALLE=4也需要>=4个DMP⽂件，也可以使⽤%U来进⾏导⼊。
nohup expdp system/**** PARALLEL=2 JOB_NAME=full_bak_job full=y dumpfile=exptest:back_%U.dmp logfile=exptest:back.log & impdp system/*** PARALLEL=2 EXCLUDE=STATISTICS JOB_NAME=full_imp cluster=no full=y dumpfile=test:back_%U.dmp
logfile=test:back_imp.log;
苹果复制粘贴⽽在11GR2后EXPDP 和 IMDP的WORKER进程会在多个INSTANCE启动，所以DIRECTORY必须在共享磁盘上，如果没有设置共享磁盘还是指定cluster=no 来防⽌报错。
当观察EXPDP/IMPDP woker的时候如下：
Import> status
Job: FULL_IMP
Operation: IMPORT
Mode: FULL
State: EXECUTING
Bytes Procesd: 150,300,713,536
Percent Done: 80
Current Parallelism: 6
Job Error Count: 0
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Dump File: /expdp/back_%u.dmp
Dump File: /expdp/back_01.dmp
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Dump File: /expdp/back_02.dmp
Dump File: /expdp/back_03.dmp
Dump File: /expdp/back_04.dmp
Dump File: /expdp/back_05.dmp
Dump File: /expdp/back_06.dmp
Dump File: /expdp/back_07.dmp
Dump File: /expdp/back_08.dmp
Worker 1 Status:
Process Name: DW00
State: EXECUTING
Object Schema: ACRUN
Object Name: T_PLY_UNDRMSG
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
Completed Objects: 3
Completed Rows: 3,856,891
Completed Bytes: 1,134,168,200
Percent Done: 83
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Worker 2 Status:
Process Name: DW01
State: EXECUTING
Object Schema: ACRUN
Object Name: T_FIN_PAYDUE
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
Completed Objects: 5
Completed Rows: 2,646,941
Completed Bytes: 1,012,233,224
Percent Done: 93
Worker Parallelism: 1
Worker 3 Status:
Process Name: DW02
State: EXECUTING
Object Schema: ACRUN
Object Name: MLOG$_T_FIN_CLMDUE
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
Completed Objects: 6
Completed Bytes: 382,792,584
Worker Parallelism: 1
Worker 4 Status:
Process Name: DW03
State: EXECUTING
Object Schema: ACRUN
Object Name: T_PAY_CONFIRM_INFO
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
Completed Objects: 5
Completed Rows: 2,443,790
Completed Bytes: 943,310,104
Percent Done: 83
Worker Parallelism: 1
Worker 5 Status:
Process Name: DW04
State: EXECUTING
Object Schema: ACRUN
Object Name: T_PLY_TGT
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
Completed Objects: 6武庚叛乱
Completed Rows: 2,285,353
Completed Bytes: 822,501,496
Percent Done: 64
Worker Parallelism: 1
Worker 6 Status:
Process Name: DW05
State: EXECUTING
Object Schema: ACRUN
Object Name: T_FIN_PREINDRCT_CLMFEE
Object Type: DATABASE_EXPORT/SCHEMA/TABLE/TABLE_DATA
1931年9月18日事变Completed Objects: 5
Completed Rows: 6,042,384
Completed Bytes: 989,435,088
Percent Done: 79
Worker Parallelism: 1
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英⽂如下：
For Data Pump Export, the value that is specified for the parallel parameter should be less than or equal to the number of files in the dump file t. Each worker or Parallel Execution Process requires exclusive access to the dump file, so having fewer dump files than the degree of parallelism will mean that some workers or PX process will be unable to write the information they are exporting. If this occurs, the worker process go into an idle state and will not be doing any work until more files are added to the job. See the explanation of the DUMPFILE parameter in the Databa Utilities guide for details on how to specify multiple dump files for a Data Pump export job.
For Data Pump Import, the workers and PX process can all read from the same files. However, if there are not enough dump files, the performance may not be optimal becau multiple threads of execution will be trying to access the same dump file. The performance impact of multiple process sharing the dump files depends on the I/O subsystem containing the dump files. For this reason, Data Pump Import should not have a value for the PARALLEL parameter that is significantly larger than the number of files in the dump file t.风衣打结
In a typical export that includes both data and metadata, the first worker process will unload the metadata: tablespaces, schemas, grants, roles, tables, indexes, and so on. This single worker unloads the metadata, and all the rest unload the data, all at the same time. If the metadata worker finishes and there are still data objects to unload, it will start unloading the data too. The examples in this document assume that there is always one worker busy unloading metadata while the rest of the workers are busy unloading table data objects.
If the external tables method is chon, Data Pump will determine the maximum number of PX process that can work on a table data object. It does this by dividing the estimated size of the table data object by 250 MB and rounding the result down. If the result is zero or one, then PX process are not ud to unload the table
The PARALLEL parameter works a bit differently in Import than Export. Becau there are various dependencies that exist when creating objects during import, everything must be done in order. For Import, no data loading can occur until the tables are created becau data cannot be loaded into tables that do not yet exist
