Manage shared memory

The following C functions can make allocations from the database server shared memory:

C UDRs
A C UDR has access to the following types of shared memory for dynamic allocations: user memory and named memory.
DataBlade® API constructor functions
A constructor function allocates its DataBlade® API data type structure in user memory. The constructor can allocate a particular data type structure with a specified memory duration (DataBlade API data type structures with a PER_ROUTINE memory duration through DataBlade API data type structures with a PER_STMT_EXEC memory duration) or the current memory duration (DataBlade API data type structures with a PER_SESSION memory duration).

The DataBlade® API provides the memory-management functions in following table for the dynamic allocation of database server shared memory.

Table 1. Memory-management functions of the DataBlade® API
Type of shared memory	Description	DataBlade® API functions
User memory	Memory that is accessible by its address only. User memory can be allocated in the current memory duration or have a specified memory duration.	mi_alloc(), mi_dalloc(), mi_realloc(), mi_zalloc(), mi_switch_mem_duration(), mi_free()
Named memory	Memory that has a name assigned and is accessible by its address or its name. Named memory has a specified memory duration.	mi_named_alloc(), mi_named_zalloc(), mi_named_get(), mi_named_free() mi_lock_memory(), mi_try_lock_memory(), mi_unlock_memory()

Important: Named memory is an advanced feature that can adversely affect your UDR if you use it incorrectly. Use it only when no regular DataBlade® API feature can perform the task you need done.

Tip: A client LIBMI application can also use DataBlade® API memory-management functions to perform dynamic allocations. However, these memory-management functions allocate memory from the client process, not from the shared memory of the database server. Therefore, memory that these functions allocate from within a client LIBMI application does not have a memory duration associated with it. For more information, see Manage memory in client LIBMI applications.

These DataBlade® API memory-management functions in Memory-management functions of the DataBlade API work correctly with the transaction management and memory reclamation of the database server. In particular, they provide the following advantages:

These functions allocate the memory from shared memory so that all VPs can access it.
The database server automatically reclaims memory allocated with these functions.
These functions establish a memory duration for the memory they allocate. When this memory duration expires, the database server automatically marks the memory for reclamation. For more information, see Choose the memory duration.