4.41 Obtaining Runtime Statistics

The predicate statistics/2 is built-in. More high level predicates are available from library library(statistics). See section A.48.

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. CPU time results are based on clock_gettime(), times() or wall time since the process was started (in that order of preference). On Windows GetProcessTimes() is used. Both clock_gettime() and GetProcessTimes() provide a nanosecond resolution interface. The actual resolution depends on the platform.

Native keys (times as float in seconds)
agcNumber of atom garbage collections performed
agc_gainedNumber of atoms removed
agc_timeTime spent in atom garbage collections
atomsTotal number of defined atoms
atom_spaceBytes used to represent atoms
c_stackSystem (C-) stack limit. 0 if not known.
cgcNumber of clause garbage collections performed
cgc_gainedNumber of clauses reclaimed
cgc_timeTime spent in clause garbage collections
clausesTotal number of clauses in the program
codesTotal size of (virtual) executable code in words
cputime(User) CPU time since thread was started in seconds
epochTime stamp when thread was started
errorsNumber of error mesages printed
functorsTotal number of defined name/arity pairs
functor_spaceBytes used to represent functors
globalAllocated size of the global stack in bytes
globalusedNumber of bytes in use on the global stack
globallimitSize to which the global stack is allowed to grow
global_shiftsNumber of global stack expansions
heapusedBytes of heap in use by Prolog (0 if not maintained)
inferencesTotal number of passes via the call and redo ports since Prolog was started
modulesTotal number of defined modules
localAllocated size of the local stack in bytes
local_shiftsNumber of local stack expansions
locallimitSize to which the local stack is allowed to grow
localusedNumber of bytes in use on the local stack
table_space_usedAmount of bytes in use by the thread's answer tables
trailAllocated size of the trail stack in bytes
trail_shiftsNumber of trail stack expansions
traillimitSize to which the trail stack is allowed to grow
trailusedNumber of bytes in use on the trail stack
shift_timeTime spent in stack-shifts
stackTotal memory in use for stacks in all threads
predicatesTotal number of predicates. This includes predicates that are undefined or not yet resolved.
indexes_createdNumber of clause index tables creates.
indexes_destroyedNumber of clause index tables destroyed.
process_epochTime stamp when Prolog was started
process_cputime(User) CPU time since Prolog was started in seconds
thread_cputimeMT-version: Seconds CPU time used by finished threads. The implementation requires non-portable functionality. Currently works on Linux, MacOSX, Windows and probably some more.
threadsMT-version: number of active threads
threads_createdMT-version: number of created threads
enginesMT-version: number of existing engines
engines_createdMT-version: number of created engines
threads_peakMT-version: highest id handed out. This is a fair but possibly not 100% accurate value for the highest number of threads since the process was created.
warningsNumber of warning mesages printed
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 ] (Used is based on ru_idrss from getrusage(). Free is based on RLIMIT_DATA from getrlimit(). Both are reported as zero if the OS lacks support. Free is -1 if getrlimit() is supported but returns infinity.)
stacks[ global use, local use ]
program[ heap use, 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 compatibility.
stack_shifts[ global shifts, local shifts, time spent ]
atoms[ number, memory use, 0 ]
atom_garbage_collection[ number of AGC, bytes gained, time spent ]
clause_garbage_collection[ number of CGC, clauses gained, time spent ]
coreSame as memory
Table 7 : Compatibility keys for statistics/2. Time is expressed in milliseconds.