Oracle-L: RE: IMPORT sloooowwww

From: Johnson, Michael <Michael.Johnson_at_oln-afmc.af.mil>
Date: Thu, 29 Aug 2002 10:23:48 -0800
Message-ID: <F001.004C2E03.20020829102348@fatcity.com>

Here is a most excellent post from Kirti Deshpande, kirti.deshpande_at_verizon.com earlier on some import / export principles that may help you.
If you like it, pass on your thanks to him.

PEACE. Mike

Prepare scripts to build tables, indexes and constraints etc.. Prebuild the tables in the target database. I am assuming that a database is already created with all the tablespaces etc..

Improving Export performance:
1) Use direct=y. That will make the export process significantly faster. 2) Along with (1), setting 'recordlength' to multiples of db_block_size or to its max value (65535) will help 'squeeze out' some more performance gain. Although, this parameter is to be used when exporting/importing on different OS where it has different default values, I use it for added performance gain. You may want to give it a trial run to see if that would help. 3) I do not export indexes.

Improving Import Performance:

1) Keep database in no-archive log mode, if it is not already so. 
2) Remember to use ignore=y since tables are already present.
3) Use commit=y to control rollback segment usage.
4) Do not import indexes by setting indexes=n (just to be sure).
5) Set buffer= to a high value, 5-10 MB should work fine (there is no

proportional gain performance in raising this value too high). 6) Set analyze=n to suppress automatic estimation of table statistics. Analyze tables using your procedures after indexes etc are built 7) For primary key constraint indexes, I keep the quota on the target tablespace to 0 to make it fail during import. (something I just find easier to remember).
8) Set log= to some log file name to capture all (good and bad) messages from the import process.
9) After the import is completed, set sort_area_size, sort_area_retained_size to a higher value (whatever is adequate and possible) to speed up index build process. Also, consider TEMPORARY type temp tablespace with properly configured initial and next (multiples of sort_area_size) extents. Make sure temp tablespace has ample room, should index build processes perform disk sorts. Also, make sure quota is okay on tablespaces for primary key constraint indexes. 10) Run all the index build scripts. Use nologging attribute and consider building indexes in parallel, if resources are available to do so. 11) Enable all the constraints etc.
12) After all indexes are successfully built, make sure the sort parameters are adjusted back to what they should be for running the db normally. Spot check and make sure everything looks fine and okay. 13) Do not forget the SQL*Net thingy.. Make necessary changes to global_name, TNSNAMES.ora and LISTENER.ora file. Bounce the listener.

14) Run your own procedures to analyze tables and indexes. 
15) Take a cold back up.  
16) Startup mount and change to archive log (if required). Open the db for

users.
17) Time to hit the door..

-----Original Message-----
Sent: Thursday, August 29, 2002 8:23 AM
To: Multiple recipients of list ORACLE-L

Oracle 8.1.7 on Solaris 8

I am testing and upgrade from 7.3.4 to 8.1.7. Because the test server is solaris 8, and I can't find the patches for 7 anymore, I am trying to upgrade via an export and import. Besides, the DB is small - less than 2G. The export was done with compress=n. There are 200+ tables to be imported. It is taking 3+ minutes per table for the import, even on tables that have 0 rows. (Though it does take longer than that for the few tables with over 50K rows).

I have tried:

Simple import.
Import with indexes=n
Import with table and constraints (but not indexes) pre-created and indexes=n ignore=y
All of the above with the buffer set to 8M (This actually slows the import down, taking 5+ minutes per table).
Increasing the sort_area_size for the DB to twice as large as it was and trying the above.

In looking at how long it takes, the table imports in a second or less, but it takes 3 minutes + to start the import of the next table. I'm not sure what it is doing for 3 minutes after the table imports.

Does anyone have any ideas how I can speed this up? 10 hours to import a 2G. DB is extreme and unacceptable.

TIA. Terry

Terry Ball, DBA
Birch Telecom
Work: 816-300-1335
FAX: 816-300-1800
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Author: Ball, Terry
INET: TBall_at_birch.com

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Author: Johnson, Michael
INET: Michael.Johnson_at_oln-afmc.af.mil

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