A method of operating a debugger to debug a program to be executed on a processor capable of executing instructions, the processor operating on data formed of data granules having associated metadata items, the method comprising: deciding to access a specified number of metadata items, where the specified number is greater than a number of metadata items accessed by each instance of a metadata access operation such that the metadata access operation needs to be performed by the processor multiple times in order to access the specified number of metadata items; and issuing at least one command to the processor to cause the processor to perform a plurality of instances of the metadata access operation in order to access in a memory system at least a subset of the specified number of metadata items; wherein: the number of metadata items accessed by each instance of the metadata access operation is non-deterministic to the debugger from the metadata access operation, such that the debugger cannot determine from the metadata access operation how many metadata items will be accessed by the processor when the processor executes that metadata access operation; at least one access indicator is provided to indicate constraining information about the number of metadata items accessed by each instance of the metadata access operation; and the plurality of instances of the metadata access operation performed in response to the at least one command is determined with reference to the at least one access indicator, whereby the plurality of instances of the metadata access operation are performed by the processor without the debugger interrogating the processor between each instance of the metadata access operation to determine progress in the number of metadata items accessed. deciding to access a specified number of metadata items, where the specified number is greater than a number of metadata items accessed by each instance of a metadata access operation such that the metadata access operation needs to be performed by the processor multiple times in order to access the specified number of metadata items; and issuing at least one command to the processor to cause the processor to perform a plurality of instances of the metadata access operation in order to access in a memory system at least a subset of the specified number of metadata items; wherein: the number of metadata items accessed by each instance of the metadata access operation is non-deterministic to the debugger from the metadata access operation, such that the debugger cannot determine from the metadata access operation how many metadata items will be accessed by the processor when the processor executes that metadata access operation; at least one access indicator is provided to indicate constraining information about the number of metadata items accessed by each instance of the metadata access operation; and the plurality of instances of the metadata access operation performed in response to the at least one command is determined with reference to the at least one access indicator, whereby the plurality of instances of the metadata access operation are performed by the processor without the debugger interrogating the processor between each instance of the metadata access operation to determine progress in the number of metadata items accessed. the number of metadata items accessed by each instance of the metadata access operation is non-deterministic to the debugger from the metadata access operation, such that the debugger cannot determine from the metadata access operation how many metadata items will be accessed by the processor when the processor executes that metadata access operation; at least one access indicator is provided to indicate constraining information about the number of metadata items accessed by each instance of the metadata access operation; and the plurality of instances of the metadata access operation performed in response to the at least one command is determined with reference to the at least one access indicator, whereby the plurality of instances of the metadata access operation are performed by the processor without the debugger interrogating the processor between each instance of the metadata access operation to determine progress in the number of metadata items accessed.