Memory Services

Memory management is one of the services that is required by cartridge developers.

The memory service allows the client to allocate or free memory chunks. Each memory chunk is associated with a duration. This allows clients to automatically free all memory associated with a duration (at the end of the duration). The duration determines the heap that is used to allocate the memory. The memory service predefines three kinds of durations: call (OCI_DURATION_CALL), statement (OCI_DURATION_STATEMENT) and session (OCI_DURATION_SESSION).

The client can also create a user duration. The client has to explicitly start and terminate a user duration. Thus, the client can control the 'length' of a user duration. Like the predefined durations, a user duration can be used to specify the allocation duration (e.g., memory chunks are freed at the end of the user duration).

Each user duration has a parent duration. A user duration terminates implicitly when its parent duration terminates. A parent duration can be call, statement, transaction, session or any other user duration. Memory allocated in the user duration comes from the heap of its parent duration.

The Oracle RDBMS memory manager already supports a variety of memory models. Currently callouts support memory for the duration of that callout. With the extension of row sources to support external indexing, there is a need for memory of durations greater than a callout.

The following functionality is supported:

• Allocate (permanent and freeable) memory of following durations
  • call to agent process

  • statement

  • session

  • shared attributes (meta-data) for cartridges

• Ability to re-allocate memory

• Ability to create a subduration memory i.e., a sub heap which gets freed up when the parent heap gets freed up. Memory for this sub heap can be allocated and freed.

• Ability to specify zeroed memory

• Ability to allocate large contiguous memory