4.39 Obtaining Runtime Statistics

statistics(+Key, -Value)

Unify system statistics determined by Key with Value. The possible keys are given in the table 5. The last part of the table contains keys for compatibility to other Prolog implementations (Quintus) for improved portability. Note that the ISO standard does not define methods to collect system statistics. Space unit is bytes^{66This may change to `cells' to enhance compatibility between the 32- and 64-bit versions.}. Times are in seconds, represented as a floating point number. The Quintus compatibility keys express times in milliseconds.

agc	Number of atom garbage-collections performed
agc_gained	Number of atoms removed
agc_time	Time spent in atom garbage-collections
cputime	(User) CPU time since Prolog was started in seconds
inferences	Total number of passes via the call and redo ports since Prolog was started.
heap	Estimated total size of the heap (see section 2.18.1.1)
heapused	Bytes heap in use by Prolog.
heaplimit	Maximum size of the heap (see section 2.18.1.1)
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
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
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
atoms	Total number of defined atoms.
functors	Total number of defined name/arity pairs.
predicates	Total number of predicate definitions.
modules	Total number of module definitions.
codes	Total amount of byte codes in all clauses.
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.
Compatibility keys (times in milliseconds)
runtime	[ CPU time, CPU time since last ] (milliseconds)
system_time	[ System CPU time, System CPU time since last ] (milliseconds)
real_time	[ Wall time, Wall time since last ] (see get_time/1)
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, 0 ]
garbage_collection	[ number of GC, bytes gained, time spent ]
stack_shifts	[ global shifts, local shifts, time spent ] (fails if no shifter in this version)
atoms	[ number, memory use, 0 ]
atom_garbage_collection	[ number of AGC, bytes gained, time spent ]
core	Same as memory

Table 5 : Keys for statistics/2

statistics

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

time(+Goal)

Execute Goal just like once/1 (i.e., leaving no choice points), but print used time, 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.