4.38 Obtaining Runtime Statistics

statistics(+Key, -Value)

Unify system statistics determined by Key with Value. The possible keys are given in the table 6. This predicate supports additional keys for compatibility reasons. These keys are described in table 7.

Native keys (times as float in seconds)
agc	Number of atom garbage collections performed
agc_gained	Number of atoms removed
agc_time	Time spent in atom garbage collections
process_cputime	(User) CPU time since Prolog was started in seconds
cputime	(User) CPU time since thread was started in seconds
inferences	Total number of passes via the call and redo ports since Prolog was started
heapused	Bytes of heap in use by Prolog (0 if not maintained)
heap_gc	Number of heap garbage collections performed. Only provided if SWI-Prolog is configured with Boehm-GC. See also garbage_collect_heap/0.
c_stack	System (C-) stack limit. 0 if not known.
stack	Total memory in use for stacks in all threads
local	Allocated size of the local stack in bytes
localused	Number of bytes in use on the local stack
locallimit	Size to which the local stack is allowed to grow
local_shifts	Number of local-stack expansions
global	Allocated size of the global stack in bytes
globalused	Number of bytes in use on the global stack
globallimit	Size to which the global stack is allowed to grow
global_shifts	Number of global-stack expansions
trail	Allocated size of the trail stack in bytes
trailused	Number of bytes in use on the trail stack
traillimit	Size to which the trail stack is allowed to grow
trail_shifts	Number of trail-stack expansions
shift_time	Time spent in stack-shifts
atoms	Total number of defined atoms
functors	Total number of defined name/arity pairs
clauses	Total number of clauses in the program
modules	Total number of defined modules
codes	Total size of (virtual) executable code in words
threads	MT-version: number of active threads
threads_created	MT-version: number of created threads
thread_cputime	MT-version: seconds CPU time used by finished threads. Supported on Windows-NT and later, Linux and possibly a few more. Verify it gives plausible results before using.

Table 6 : Keys for statistics/2. Space is expressed in bytes. Time is expressed in seconds, represented as a floating point number.

Compatibility keys (times in milliseconds)
runtime	[ CPU time, CPU time since last ] (milliseconds, excluding time spent in garbage collection)
system_time	[ System CPU time, System CPU time since last ] (milliseconds)
real_time	[ Wall time, Wall time since last ] (integer seconds. See get_time/1)
walltime	[ Wall time since start, Wall time since last] (milliseconds, SICStus compatibility)
memory	[ Total unshared data, free memory ] (Uses getrusage() if available, otherwise incomplete own statistics.)
stacks	[ global use, local use ]
program	[ heap, 0 ]
global_stack	[ global use, global free ]
local_stack	[ local use, local free ]
trail	[ trail use, trail free ]
garbage_collection	[ number of GC, bytes gained, time spent, bytes left ] The last column is a SWI-Prolog extension. It contains the sum of the memory left after each collection, which can be divided by the count to find the average working set size after GC. Use [Count, Gained, Time|_] for compatiblity.
stack_shifts	[ global shifts, local shifts, time spent ]
atoms	[ number, memory use, 0 ]
atom_garbage_collection	[ number of AGC, bytes gained, time spent ]
core	Same as memory

Table 7 : Compatibility keys for statistics/2. Time is expressed in milliseconds.

statistics

Display a table of system statistics on the current output stream.

time(:Goal)

Execute Goal just like call/1 and print time used, number of logical inferences and the average number of lips (logical inferences per second). Note that SWI-Prolog counts the actual executed number of inferences rather than the number of passes through the call and redo ports of the theoretical 4-port model. If Goal is non-deterministic, print statistics for each solution, where the reported values are relative to the previous answer.