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Data Pump Import Best Practices

Best Practices and recommended parameter settings for Oracle Data Pump import operations.

General Recommendations​

caution

Don't use sys as sysdba for the import

Data Pump Patching​

Apply the latest Data Pump Bundle Patch.

Diagnostics​

Always specify the LOGTIME=ALL and METRICS=YES parameters to log more timing/worker information and show the access_method per table in the logfile.

Here are some example logfiles with different diagnostics settings:

  • Logfile Example (Default Settings):
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
. . imported "SCHEMA1"."TABLE1"                          5.117 KB       3 rows
  • Logfile Example (LOGTIME=ALL):
22-MAY-23 11:14:05.310: Processing object type SCHEMA_EXPORT/TABLE/TABLE
22-MAY-23 11:14:06.128: Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
22-MAY-23 11:14:06.347: . . imported "SCHEMA1"."TABLE1"                          5.117 KB       3 rows
  • Logfile Example (METRICS=YES):
W-1 Startup took 0 seconds
W-1 Master table "SYSTEM"."SYS_IMPORT_SCHEMA_01" successfully loaded/unloaded
W-1 Processing object type SCHEMA_EXPORT/TABLE/TABLE
W-1      Completed 1 TABLE objects in 1 seconds
W-1      Completed by worker 1 1 TABLE objects in 1 seconds
W-1 Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
W-1 . . imported "SCHEMA1"."TABLE1"                          5.117 KB       3 rows in 0 seconds using direct_path
  • Logfile Example (LOGTIME=ALL + METRICS=YES):
22-MAY-23 11:17:59.424: W-1 Startup took 0 seconds
22-MAY-23 11:17:59.687: W-1 Master table "SYSTEM"."SYS_IMPORT_SCHEMA_01" successfully loaded/unloaded
22-MAY-23 11:18:03.001: W-1 Processing object type SCHEMA_EXPORT/TABLE/TABLE
22-MAY-23 11:18:03.949: W-1      Completed 1 TABLE objects in 0 seconds
22-MAY-23 11:18:03.949: W-1      Completed by worker 1 1 TABLE objects in 0 seconds
22-MAY-23 11:18:04.251: W-1 Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
22-MAY-23 11:18:04.676: W-1 . . imported "SCHEMA1"."TABLE1"                          5.117 KB       3 rows in 0 seconds using direct_path

Target Database​

STREAMS_POOL_SIZE​

Data Pump uses Advanced Queuing so STREAMS_POOL_SIZE needs to be set to a minimum of 256 MB.

  • Check the current size:

    select current_size/1024/1024 as current_size_mb
    from v$sga_dynamic_components 
    where component='streams pool';

  • Set STREAMS_POOL_SIZE to minimum of 256 MB:

    alter system set streams_pool_size=256m scope=both;

Statistics​

After the import gather statistics on the target database or transport the status using DBMS_STATS.
Additionally make sure the dictionary stats (SYS, SYSTEM) are current after the import:

exec dbms_stats.gather_schema_stats ('SYS');
exec dbms_stats.gather_schema_stats ('SYSTEM');

Overview of the most important and relevant Data Pump import parameters. Click here for examples.

LOGTIME=ALL​

Always specify the logtime diagnostics parameter to log more timing information.

METRICS=YES​

Always specify the metrics diagnostics parameter to show more worker information and the access_method per table in the logfile.

PARALLEL=n​

note

This parameter is only valid for the Enterprise Edition

Use parallel processes to speed up the import operation. The number of processes depends on the actual number of cpus on the target system.

Degree of parallelism:

PlatformDegree
Cloud OCPU1 x OCPU count
Cloud ECPU.25 x ECPU count
On-prem x862 x CPU cores count
On-prem (Other)Depends
info

The number of dump files does not affect the parallel import settings.
You can use more parallel processes than dump files available.

EXCLUDE=STATISTICS​

Exclude optimizer statistics from the import operation. After the import the statistics should be gathered on the target db or transported from the source database with DBMS_STATS.

exclude=statistics

TRANSFORM=LOB_STORAGE:SECUREFILE​

SecureFiles is the default LOB storage option now and all binary data types should be migrated from BasicFile LOBs to SecureFile LOBs.

info

BasicFile LOBs do not allow parallel DML.

Example:

impdp ... transform=lob_storage:securefile

Optional Parameters​

Checksum​

This is a new feature available starting from Oracle 21c and can be used to verify the file integrity on import when a checksum was calculated during export. It's possible to only run a verify of the checksum with the VERIFY_ONLY parameter.

Examples: 

impdp ... verify_only=yes
impdp ... verify_checksum=yes

Multitenant​

To avoid any noisy neighbours if the resources are insufficient set the following parameters:

  • Restrict the number of concurrent Data Pump jobs for a PDB

    alter system set max_datapump_jobs_per_pdb=n;

  • Restrict the parallel degree setting for a Data Pump Job

    alter system set max_datapump_parallel_per_job=n container=all;

Examples​

impdp userid=system@pdb1 \
    schemas=SCHEMA1 \
    directory=DATA_PUMP_DIR \
    dumpfile=dump%L.dmp \
    logfile=impdp.log \
    parallel=2 \
    transform=lob_storage:securefile \
    exclude=statistics \
    logtime=all \
    metrics=yes