Memory Management

Dynamic Server provides several options to help you manage memory to optimize performance.

Dynamically Sharing Memory

All applications that use the same database server share data in the memory space of the database server. The database server adds memory dynamically as it needs it. The database server administrator can control the amount of shared memory that is available to the database server.

Buffering Transactions

You can determine how the database server logs transactions. A transaction is a collection of SQL statements that is treated as a single unit of work. Your logs can be buffered or unbuffered. Buffered logging holds transactions in memory until the buffer is full, regardless of when the transaction is committed.

For information on how to manage the various aspects of memory to increase performance, see your IBM Informix Performance Guide and SQL Enhancements. For information on transaction logging, see the IBM Informix Administrator's Guide.

Using NFS-Mounted Directories

An IBM Informix storage space can reside on an NFS-mounted directory only if the vendor of that NFS device is certified by IBM Informix. For information about NFS products that you can use to mount a storage space for an IBM Informix database server, see the IBM Informix product family Web site at http://www.ibm.com/software/data/informix.

Fragmentation

Dynamic Server supports table and index fragmentation over multiple disks. Fragmentation lets you group rows within a table according to a distribution scheme. Fragmentation improves performance on large databases.

Dynamic Server supports the following fragmentation schemes:

• Round-robin fragmentation places rows one after another in fragments, rotating through the series of fragments to distribute the rows evenly.
• Expression-based fragmentation puts rows that contain specified values in the same fragment. You specify a fragmentation expression that defines criteria for assigning a set of rows to each fragment, either as a range rule or some arbitrary rule.

For information on the fragmentation strategies, see the IBM Informix Database Design and Implementation Guide. For information about how to create a fragmentation strategy to enhance database performance, see your IBM Informix Performance Guide.