# Allocation Callback

When `mco_register_alloc_callback()` or `mco_register_disk_alloc_callback()` is called it must pass a callback function defined as follows:

        typedef MCO_RET (*mco_alloc_callback_t)(mco_db_h db, mco_offs_t used);

The parameters are as follows:

db | A valid database connection handle.
used | Current memory usage in bytes

An example of an allocation callback implementation is provided in the SDK sample "samples/native/core/21-oveflow/transient".