If you are working as developer/DBA probably you are quite often asked to migrate some rows from one database to another – usually people reference to the rows as “metadata” rows. Rows that driving your business !

If you need to prepare such rows for migrations there are a lot of methods to do it

just copy the rows using database link from one database to another
export/import the rows using tools like expdp/impdp
prepare manually scripts with INSERT statements

I would like to focus on the last method. It’s very popular to keep metadata in some files as number of INSERTs for backup/migrations/versioning etc.

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This article presents how to install Fedora 25 – Live Workstation version.

I assume you have already downloaded Fedora 25 64 bit Live Workstation(about 1,3 G) and you know how to use VirtualBox 64 bit(100M). Create virtual machine with default settings for Linux Fedora 64 bit. 2GB ram and 64G(includes extra space for Oracle installations) for disk is enough plus increase video memory to 128M. Rest of options you can keep default.

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You can find original user password in table USER$. Because of security improvements it is not exposed in DBA_USERS view anymore since version 10G. Moreover password is hashed so once set you are not able to know original value. Access to USER$ is as well very restricted.

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Hakan factor

The Hakan factor is used to unique map rows in a Bitmap Index to the rows in the base table. This factor is related to the max number of rows that can be stored in a single block of a table. Several factors like the column type and not null constraints influence the Hakan factor. The factor will also be recalculated when a table is modified until there is the first bitmap Index is created. Than the Hakan factor has to be protected for the existing bitmap indexes.

If a new table created to exchange data with the partitioned table, with a table layout, that include columns added after the bitmap index creation on the partitioned table, will most likely result in a different Hakan factor.

Errors

If the Hakan Factor do not match during exchange partitions, the prognosis is either of the error messages below:

• ORA-14642: “Bitmap index mismatch for tables in ALTER TABLE EXCHANGE PARTITION”
• ORA-14643: “Hakan factor mismatch for tables in ALTER TABLE EXCHANGE PARTITION”

The error can appear only if you exchange a partition with bitmap indexes

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Autonomous transaction – is an independent transaction called from another transaction which is the main transaction.

Features of autonomous transaction

• autonomous transaction doesn’t see uncommitted changes made by main transaction
• committed changes in autonomous transaction are visible in main transaction
• autonomous transaction can call other autonomous transaction. There are no limit how many levels of autonomous transaction can be called

Special pragma AUTONOMOUS_TRANSACTION is introduced in PL/SQL. The pragma instructs the database that executed code is to be executed as new autonomous transaction independent from main transaction.

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