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Informix to Oracle migration tips

Oracle Database Tips by Donald Burleson

Question:  My management is sick of Informix and I've been charged with migrating the Informix database onto Oracle.  migration from Informix Dynamic Server Version 7.30.UC10X3 running on UnixWare to Oracle10g running on Redhat Linux. currently, I'm using the Oracle Migration Workbench. 

I see two approaches, a manual unload and reload into Oracle, or using the Oracle Migration Workbench.  What's the best practice for migrating from Informix to Oracle?

Answer:  First, it's a best practice to move from Informix to Oracle, so you are off to a great start!  First, make sure to completely verify the migration on a test environment before doing it in production.  Also, for migrating the SQL, some consultancies have scripts to change Informix SQL to Oracle SQL, so changing the Informix SQL is easy.

For each migration approach, I have these tips:

Using Oracle Migration Workbench (OMW) to migrate from Informix to Oracle

There are sample capture scripts available for Informix with the Oracle Migration Workbench. If you check under the installation directory for the migration workbench, there should be a subdirectory for Informix that has example capture scripts.  The Oracle Workbench migration workbench provides an editor when parsing data between environments. You may need to tweak some of the code that does not convert cleanly and it's a best practice to scrub the data before loading to Oracle just to be on the safe side.

Manual migrate from Informix to Oracle

If you don't want to use the Oracle Migration Workbench, you can simply export and import, using standard Informix and Oracle utilities:

1 - spool the Informix rows to a flat file (with appropriate delimiters), and re-load using Oracle SQL*Loader:

2 - After loading tables, create the indexes, modifying the Informix "create index" DDL.

3 - Convert the ex-Informix application to change the Informix SQL to Oracle SQL.

Adjusting Informix data types

Question:  I cannot translate this table from Informix to Oracle:

create table test_table
(userid integer,
first_name varchar(128),
last_name varchar(128),
mod_date datetime year to fraction(3),
username varchar(32)

Answer:  Note that the constraint syntax is slightly different in Informix, and easy to change.  For details on using constraints, see the book "Easy Oracle Jumpstart".

As to the "Year to fraction" datatype, the docs note:

"The Informix Dynamic Server DATETIME data type has higher precision, YEAR to Fraction of Second, than the Oracle DATE data type, Year to Second. The fractional second information, if specified in the Informix Dynamic Server column definition, is lost in the migration."
If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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