Choose the memory duration

Because a C UDR executes in the memory space of the database server, its dynamic memory allocations can increase the memory usage of the database server. For this reason, it is important that a UDR release its dynamically allocated memory as soon as it no longer needs to access this memory.

To help ensure that unneeded memory is freed, the database server associates a memory duration with memory allocation made from its shared memory. The portion of shared memory that the database server provides for dynamic allocation by C UDRs is organized into several memory pools. Each memory pool is associated with a memory duration, which specifies the lifetime of the memory allocated from the pool. Keeping related memory allocations in one pool helps to reduce memory fragmentation.

The following figure shows a schematic representation of the shared memory of the database server, including the memory-duration memory pools.

Figure 1. Memory-duration memory pools in database server shared memory

Tip: For more information about the use and structure of database server memory pools, see your HCL Informix® Administrator's Guide. For more information about how to monitor the amount of shared memory that exists in each of the memory pools, see Monitor shared memory.

When the database server calls a UDR, it creates a memory context. This memory context records all of the allocations that the UDR makes before the routine returns. The UDR might run for some time, calling other UDRs or DataBlade API functions. The database server automatically reclaims shared memory based on its memory duration. When a particular memory duration expires, the database server marks the associated memory pool for deallocation.