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Statistics relating to memory usage, run time, and garbage collection,
including information about which areas of memory have overflowed and
how much time has been spent expanding them, can be displayed by
calling statistics/0
.
The output from statistics/0
looks like this:
memory (total) 3334072 bytes global stack 1507184 bytes: 2516 in use, 1504668 free local stack 49296 bytes: 276 in use, 49020 free trail stack 34758 bytes: 248 in use, 34510 free choice stack 34874 bytes: 364 in use, 34510 free program space 1707960 bytes: 1263872 in use, 444088 free program space breakdown: compiled code 575096 bytes atom 166528 bytes predicate 157248 bytes try_node 144288 bytes sw_on_key 105216 bytes incore_info 51096 bytes atom table 36864 bytes interpreted code 13336 bytes atom buffer 2560 bytes SP_malloc 2288 bytes FLI stack 2048 bytes miscellaneous 1640 bytes BDD hash table 1560 bytes source info (B-tree) 1024 bytes numstack 1024 bytes int_info 880 bytes file table 400 bytes source info (itable) 328 bytes module 320 bytes source info (lheap) 80 bytes foreign resource 32 bytes all solutions 16 bytes 4323 atoms (151927 bytes) in use, 1044252 free No memory resource errors 0.020 sec. for 7 global, 20 local, and 0 choice stack overflows 0.060 sec. for 15 garbage collections which collected 5461007 bytes 0.000 sec. for 0 atom garbage collections which collected 0 atoms (0 bytes) 0.000 sec. for 4 defragmentations 0.000 sec. for 7 dead clause reclamations 0.000 sec. for 0 dead predicate reclamations 39.410 sec. runtime ======== 39.490 sec. total runtime 109.200 sec. elapsed time
Note the use of indentation to indicate sub-areas. That is, memory contains the program space and the four stacks: global, local, choice, and trail.
The memory (total) figure shown as “in use” is the sum of the spaces for the program space and stacks. The “free” figures for the stacks are for free space within those areas. However, this free space is considered used as far as the memory (total) area is concerned, because it has been allocated to the stacks. The program space is not considered to have its own free space. It always allocates new space from the general memory (total) free area.
If a memory resource error has occurred previously in the execution, then the memory area for which memory could not be allocated is displayed.
Individual statistics can be obtained by statistics/2
, which
accepts a keyword and returns a list of statistics related to that
keyword.
The keys and values for statistics(Keyword, Value)
are summarized below. The keywords core
and heap
are
included to retain compatibility with other Prologs. Times are given
in milliseconds and sizes are given in bytes.
Keyword
Value
runtime
[since start of Prolog,since previous statistics]
These refer to CPU time used while executing, excluding time spent
in memory management tasks or in system calls.
The second element is the time since the latest call to
statistics/2
with this key or to statistics/0
.
total_runtime
[since start of Prolog,since previous statistics]
These refer to total CPU time used while executing, including memory
management tasks such as garbage collection but excluding system calls.
The second element is the time since the latest call to
statistics/2
with this key or to statistics/0
.
walltime
[since start of Prolog,since previous statistics]
These refer to absolute time elapsed.
The second element is the time since the latest call to
statistics/2
with this key or to statistics/0
.
global_stack
[size used,free]
This refers to the global stack, where compound terms are stored. The
values are gathered before the list holding the answers is allocated.
Formed from basic values below.
local_stack
[size used,free]
This refers to the local stack, where recursive predicate environments
are stored. Formed from basic values below.
trail
[size used,free]
This refers to the trail stack, where conditional variable bindings are
recorded. Formed from basic values below.
choice
[size used,free]
This refers to the choice stack, where partial states are stored
for backtracking purposes. Formed from basic values below.
memory
core
[size used,0]
These refer to the amount of memory actually allocated by the Prolog
engine. The zero is there for compatibility with other Prolog
implementations. Formed from basic values below.
program
heap
[size used,size free]
These refer to the amount of memory allocated for the database, symbol
tables, and the like. Formed from basic values below.
garbage_collection
[no. of GCs,bytes freed,time spent]
Formed from basic values below.
stack_shifts
[no. of global shifts,no. of local/choice shifts,time spent]
Formed from basic values below.
atoms
[no. of atoms,bytes used,atoms free]
The number of atoms free is the number of atoms allocated (the
first element in the list) subtracted from the maximum number of atoms,
i.e. 262143 (33554431) on 32-bit (64-bit) architectures. Note that
atom garbage collection may be able to reclaim some of the
allocated atoms. Formed from basic values below.
atom_garbage_collection
[no. of AGCs,bytes freed,time spent]
Formed from basic values below.
defragmentation
[no. of defragmentations,time spent]
Formed from basic values below.
memory_used since release 4.1
bytes used
memory_free since release 4.1
bytes free
global_stack_used since release 4.1
bytes used
global_stack_free since release 4.1
bytes free
local_stack_used since release 4.1
bytes used
local_stack_free since release 4.1
bytes free
trail_used since release 4.1
bytes used
trail_free since release 4.1
bytes free
choice_used since release 4.1
bytes used
choice_free since release 4.1
bytes free
atoms_used since release 4.1
bytes used
atoms_nbused since release 4.1
atoms used
atoms_nbfree since release 4.1
atoms free
ss_global since release 4.1
number of global stack shifts
ss_local since release 4.1
number of local stack shifts
ss_choice since release 4.1
number of choice stack shifts
ss_time since release 4.1
time spent stack shifting
gc_count since release 4.1
number of garbage collections
gc_freed since release 4.1
number of bytes freed
gc_time since release 4.1
time spent collecting garbage
agc_count since release 4.1
number of atom garbage collections
agc_nbfreed since release 4.1
number of garbage collected atoms
agc_freed since release 4.1
number of bytes freed by atom garbage collected
agc_time since release 4.1
time spent garbage collected atoms
defrag_count since release 4.1
number of memory defragmentations
defrag_time since release 4.1
time spent defragmenting memory
dpgc_count since release 4.1
number of dead predicate reclamations
dpgc_time since release 4.1
time spent reclaiming dead predicates
dcgc_count since release 4.1
number of dead clause reclamations
dcgc_time since release 4.1
time spent reclaiming dead clauses
memory_culprit since release 4.1
memory bucket in which latest memory resource error occurred
memory_buckets since release 4.1
list of bucket-size pair
where size is the amount of memory in use for memory bucket bucket.
jit_count since release 4.3
number of JIT-compiled predicates
This is zero when JIT compilation is not available.
jit_time since release 4.3
time spent JIT-compiling predicates
This is zero when JIT compilation is not available.
To see an example of the use of each of these keywords, type
| ?- statistics(K, L).
and then repeatedly type ‘;’ to backtrack through all the possible
keywords. As an additional example, to report information on the runtime of
a predicate p/0
, add the following to your program:
:- statistics(runtime, [T0| _]), p, statistics(runtime, [T1|_]), T is T1 - T0, format('p/0 took ~3d sec.~n', [T]).
See mpg-ref-statistics.