impdp characteristic 特性:
1, the dump file by expdp does not contain index data, although it contains the DDL statements of index . I guess it's because of the ROWID . When you load data into the destination table by impdp. The ROWID value of index will get changed. So it is meaningless store index data in dump file.
2, table_exists_action = append.
when impdp data , if the table which will be loaded already exists in the destination . this parameter will skip the TABLE DDL statement. Just load data into dest table. Note it will also skip the DDL of index creation of the table.
3, skip_unusable_indexes =y
If you do not specify this parameter, and if the dest index is in unusable state. The status of index depdend on the DDL of dumpfile.IF dumpfile does not contain DDL OF unusable INDEX, then index status stay unchanged. or droped (table_exists_action=replace)
If you clearly specify the parameter skip_unusable_indexes =y, then impdp will skip the index maintance , after load data. The index state is unusable still.
4, the destination table with one index degrade performance for 50% about.
[@more@]来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/350519/viewspace-1042157/ ，如需转载，请注明出处，否则将追究法律责任。
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