Welcome
Migrating and upgrading
You can upgrade to the 15.0.0 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 HCL Informix® Migration Guide describes how to move data manually between databases, servers, and computers.
Migration to and reversion from 15.0.0
Reverting from Version 15.0.0
As long as your Version 15.0.0 instance is running in compatibility mode, 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 Version 15.0.0, 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 Version 15.0.0 to the database server from which you migrated, if you have not added any extensions to the Version 15.0.0 database server and you are not reverting from a newly created instance.

HCL Informix® V15.0.0 documentation
Welcome to the documentation for HCL Informix® 15.0.0 and related client tools and products.
Product overview
HCL Informix® is a fast and scalable database server that manages traditional relational, object-relational, and dimensional databases. Its small footprint and self-managing capabilities are suited to embedded data-management solutions.
Installing
These topics describe how to install HCL Informix® database servers, client products, and modules.
Administering
In addition to administering the database server, you can tune performance, replicate data, and archive data.
Migrating and upgrading
You can upgrade to the 15.0.0 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 HCL Informix® Migration Guide describes how to move data manually between databases, servers, and computers.
  - Overview of migration
  - Migration to and reversion from 15.0.0
    - Preparing for migration to Version 15.0.0
      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.
    - and Upgrading
      The server nodes in your Enterprise Replication (ER) domain can run different versions and fixpack levels. On the other hand, new features might only be available between servers running the new version, and administrative ‘cdr’ commands should be run from the newest version environment.
    - 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 15.0.0
      When you migrate to a new version of Informix®, you must complete required migration and post-migration tasks.
    - Reverting from Version 15.0.0
      As long as your Version 15.0.0 instance is running in compatibility mode, 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 Version 15.0.0, 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 Version 15.0.0 to the database server from which you migrated, if you have not added any extensions to the Version 15.0.0 database server and you are not reverting from a newly created instance.
        Reversion requirements and limitations
        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® Version 15.0.0 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 Version 15.0.0 data
        Verify the integrity of your Version 15.0.0 data, if you did not do this after you migrated.
        Back up Version 15.0.0
        Before you begin the reversion, make a complete level-0 backup of Informix® Version 15.0.0.
        Resolve outstanding in-place alter operations
        Resolving outstanding in-place alter operations is a requirement before converting to Version 15.0.0. If it becomes necessary to revert to a previous version you must also resolve any 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 extensions
        When or SQL Registration are used to register an extension in a database, the ifxmngr module, which manages extensions, is registered first. If you need to revert from Version 15.0.0, and you ran against a database, you must remove all extensions.
      - Reverting from Version 15.0.0
        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
Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
Embedding Informix®
When you embed HCL Informix®, you can use enterprise-class high-availability and high performance with embeddability features such as easy programmability, a small disk and memory footprint, and silent deployment.
Extending Informix®
Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix includes many built-in extensions that are fully integrated in the database server. Informix also provides modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix.
Data warehousing
In addition to designing and implementing Informix® dimensional databases, you can use tools to create data warehouse applications and optimize your data warehouse queries.
Designing databases
The first step in creating a relational database is to construct a data model, which is a precise, complete definition of the data you want to store. After you prepare your data model, you must implement it as a database and tables. To implement your data model, you first select a data type for each column and then you create a database and tables and populate the tables with data. You can also implement fragmentation strategies and control access to your data.
JSON compatibility
You can use the popular JSON-oriented query language created by MongoDB to interact with data stored in HCL Informix®.
Security
You can secure your Informix® database server and the data that is stored in your Informix databases. You can encrypt data, secure connections, control user privileges and access, and audit data security.
SQL programming
You can use the HCL Informix® implementation of the SQL language to develop applications for Informix database servers.
Troubleshooting HCL Informix®
Several troubleshooting techniques, tools, and resources are available for resolving problems that you encounter in your HCL Informix® database server environment.

Review the database schema prior to reversion

You must review your database schema to determine if reversion is possible. You can revert from Version 15.0.0 to the database server from which you migrated, if you have not added any extensions to the Version 15.0.0 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 any new SPL routines have been created in Informix® Version 15.0.0 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 ids_mig_084.html#ids_mig_084 for limitations on reversion to previous databases and prerequisite steps you must take before you revert.