IFX_LARGE_PAGES environment variable

The IFX_LARGE_PAGES environment variable specifies whether the database server can use large pages on platforms where the hardware and the operating system support large pages of shared memory. If this is enabled in the server environment, IBM® Informix® can use the large pages for non-message shared memory segments that are located in physical memory.

The IFX_LARGE_PAGES environment variable is supported only on AIX®, Solaris, and Linux operating systems. The setting of IFX_LARGE_PAGES has no effect on Informix if the operating system does not support large pages, or if large pages are not configured on the system.

You can specify either 1 or 0 to set this environment variable.
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The use of large pages is disabled. This is the default on AIX systems.
The use of large pages is enabled. This is the default on Solaris and Linux systems.

The DBSA must use operating system commands to configure the large pages. See the operating system documentation for the configuration procedures.

Informix can use large pages for non-message shared memory segments that are locked in physical memory, if sufficient large pages are configured and available. The RESIDENT configuration parameter controls whether a shared memory segment is locked in physical memory, so that the segment cannot be swapped. If there are insufficient large pages to hold a segment, the segment might contain a mixture of large pages and regular pages.

On AIX the large pages used by Informix are 16 MB in size.

On Linux x86_64 the large pages used by Informix are defined by the Hugepagesize entry in the /proc/meminfo file.

Informix aligns the segment address and rounds up to the segment size automatically. In addition to messages regarding rounding, the server prints an informational message to the server log file whenever it attempts to use large pages to store a segment.

When IFX_LARGE_PAGES is enabled, the use of large pages can offer significant performance benefits in large memory configurations.