Components supporting high availability and scalability

HCL Informix® database software can be customized to create systems that provide uninterrupted services, minimize maintenance and downtime, automatically redirect client connection requests to the most appropriate database servers, and distribute both processing and storage across hardware.

High-availability clusters

A high-availability cluster consists of a primary server that contains the master copy of data, and is securely networked to at least one secondary server that is synchronized with the primary server or has access to the primary server's data. Transactions are sent to secondary servers after they are committed on the primary server, so database data is reliable. If the primary server fails, a secondary server can become the primary server, and client connections can be redirected to the new primary server.

High-availability cluster servers are configured with identical hardware and software. High-availability cluster servers can be in close proximity or geographically remote from each other, and applications can securely connect to any of the cluster servers.

There are three types of secondary servers:
  • Shared-disk (SD) secondary servers, which share disk space with the primary server.
  • High-availability data replication (HDR) secondary servers, which maintain synchronously or asynchronously updated copies of the entire primary server and can be accessed quickly if the primary server fails.
  • Remote stand-alone (RS) secondary servers, which maintain asynchronously updated copies of the entire primary server, and can serve as remote-backup servers in disaster-recovery scenarios.

Enterprise Replication

Using Enterprise Replication, you can maintain complete or partial copies of your data across multiple servers by replicating transactions. Data is replicated asynchronously through transactions captured from the logical log. If a remote database server or network failure occurs, a local database server can service local users, and store transactions to be replicated until remote servers become available. At each database server, Enterprise Replication reads the logical logs to capture locally originating transactions, and then replicates those transactions to other database servers in the Enterprise Replication domain.

Shard clusters

HCL Informix can horizontally partition (shard) a table or collection across multiple database servers. The set of database servers that data is sharded across is called a shard cluster, and each of the database servers in the set is a shard server. Distributing rows or documents across a shard cluster reduces the size of the associated index on each shard server, and distributes performance across your hardware. As your database grows in size, you can scale up by adding more database servers. Horizontal partitioning is also known as sharding.

Rows or documents that are inserted on one shard server can be replicated or sent to other shard servers, depending on the sharding rules you specify. Queries that are performed on a shard server can select data from other shard servers in a shard cluster. When data is sharded based on a replication key that specifies certain segmentation characteristics, queries can skip shard servers that do not contain relevant data. This query optimization is another benefit that comes from data sharding.

Connection management

The Connection Manager is a utility that can monitor the workload and status of database servers in high-availability clusters, Enterprise Replication domains, grids, and server sets, and then use a redirection policy to send client connection requests to the most appropriate database server. Connection Managers can also act as proxy servers to handle client/server communication and circumvent connection issues that are related to firewalls.

Connection Managers can control failover for high-availability clusters, automatically promoting secondary servers to the role of the primary server if the original primary server fails.

If a partial network failure occurs, Connection Managers can prioritize connections between application servers and the primary server of a high-availability cluster, to better define failover.


A grid is a set of interconnected replication servers, where SQL commands can be propagated from one server to all the others. Grids provide an easier way to administer a large group of servers, update database schemas, run stored procedures and user-defined routines, and administer replication.

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