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Migrating and upgrading
You can upgrade to the 14.10 release of HCL Informix® or migrate from other database servers to Informix. Upgrading is an in-place migration method that uses your existing hardware and operating system software. Some changes to the Informix database server can affect upgrading from a previous release.
Migrating Informix® database systems
The Informix® Migration Guide describes how to move data manually between databases, servers, and computers.
Migration to and reversion from 14.10
Reverting from Informix® Version 14.10
You can revert to the version of the database server from which you migrated. When you run the reversion utility, you specify the target server for reversion and then Informix® checks your database. If necessary, Informix might tell you to drop new objects, before automatically converting your data into the target server.
Preparing to revert
If you used , you must prepare your system for reversion to the pre-migration version of the database server.
Review the database schema prior to reversion
You must review your database schema to determine if reversion is possible. You can revert from Informix® to the database server from which you migrated, if you have not added any extensions to the database server and you are not reverting from a newly created instance.

Migrating and upgrading
You can upgrade to the 14.10 release of HCL Informix® or migrate from other database servers to Informix. Upgrading is an in-place migration method that uses your existing hardware and operating system software. Some changes to the Informix database server can affect upgrading from a previous release.
- Migrating Informix® database systems
  The Informix® Migration Guide describes how to move data manually between databases, servers, and computers.
  - Overview of migration
  - Migration to and reversion from 14.10
    - Preparing for migration to Version 14.10
      Before you install the new version of Informix®, you must prepare the database server environment for migration by performing specified pre-migration tasks. If you are also migrating from 32-bit to 64-Bit database servers, you must perform additional tasks.
    - Enterprise Replication and migration
      You must coordinate the migration of all servers that are involved in data replication.
    - High-availability cluster migration
      You must coordinate the migration and reversion of all servers that are involved in high-availability clusters. You can use a rolling upgrade in some cases to update servers while the cluster is online, with minimal interruption to client applications. Otherwise, you must schedule cluster downtime to upgrade the servers. A cluster must be offline to reverse an upgrade or revert to an earlier release.
    - Migrating to Informix® 14.10
      When you migrate to a new version of Informix®, you must complete required migration and post-migration tasks.
    - Reverting from Informix® Version 14.10
      You can revert to the version of the database server from which you migrated. When you run the reversion utility, you specify the target server for reversion and then Informix® checks your database. If necessary, Informix might tell you to drop new objects, before automatically converting your data into the target server.
      - Preparing to revert
        If you used , you must prepare your system for reversion to the pre-migration version of the database server.
        Review the database schema prior to reversion
        You must review your database schema to determine if reversion is possible. You can revert from Informix® to the database server from which you migrated, if you have not added any extensions to the database server and you are not reverting from a newly created instance.
        Reversion requirements and limitations
        If you used the new database server, you must review a list of reversion requirements and limitations, and then complete any prerequisite tasks before you revert. If the reversion restrictions indicate that you must drop objects from the database, you can unload your data and then reload it in the prior database server.
        Check and configure available space for reversion
        You must be sure you have enough space for reversion to the source database server.
        Save copies of the current configuration files
        Save copies of the ONCONFIG and concsm.cfg files for when you migrate to Informix® again.
        Save system catalog information
        If your current database server instance uses secure-auditing masks or external spaces, and you want to preserve the associated catalog information, you must unload these system catalog tables before you revert.
        Verify the integrity of the data
        Verify the integrity of your data, if you did not do this after you migrated.
        Back up Informix®
        Before you begin the reversion, make a complete level-0 backup of Informix® .
        Resolve outstanding in-place alter operations
        Resolving outstanding in-place alter operations is not a requirement before converting to a higher database server version. However, if it becomes necessary to revert to a previous version you must resolve new outstanding in-place alter operations first.
        Remove unsupported features
        Before you revert, remove all features that your older database server does not support.
        Remove new BladeManager extensions
        When BladeManager or SQL Registration are used to register an extension in a database, the ifxmngr Client SDK module, which manages extensions, is registered first. If you need to revert from , and you ran BladeManager against a database, you must remove all BladeManager extensions.
      - Reverting from Informix®
        After preparing to revert, run the reversion utility and prepare to use the original database server.
  - Migration of data between database servers
  - Data migration utilities

Review the database schema prior to reversion

You must review your database schema to determine if reversion is possible. You can revert from Informix® to the database server from which you migrated, if you have not added any extensions to the database server and you are not reverting from a newly created instance.

To review the database schema to determine if reversion is possible:

Run the dbschema utility command.
For example, run the following command to display information about the database db1:
```
dbschema -d db1 -ss
```
Determine if the schema file contains SQL statements that the earlier database server does not support.
Determine if the database contains features, such as long identifiers, that the earlier database server does not support.
Determine if any new SPL routines have been created in Informix® or if any routines were imported using dbimport.
Determine if tables or indexes using expression fragmentation had expressions changed or new fragments added.
Identify any new triggers, procedures, or check constraints.

See Reversion requirements and limitations for limitations on reversion to previous databases and prerequisite steps you must take before you revert.