Date: Tue, 29 Dec 1998 17:46:54 -0500
Reply-To: "Self, Karsten" <Karsten.Self@SCHWAB.COM>
Sender: "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From: "Self, Karsten" <Karsten.Self@SCHWAB.COM>
Subject: SAS trap -- memory allocation, _TEMPORARY_ arrays,
and char lengt h < 8
Content-Type: text/plain
SAS requires at least 8 bytes per array element for a temporary array. It
is possible to specify arrays of elements less than 8 bytes, but memory
allocation is still based on a minimum of 8 bytes per cell. Assignment and
values _do_ correspond to the specified length (e.g.: a 20 byte string will
be truncated to 4 bytes if a length of 4 is specified).
Lengths _greater_ than 8 do result in greater memory usage, though not in a
strictly linear fashion.
The issue of storage with short variables arises when building massive
arrays for purposes such as in-memory processing of hash tables and the
like. Common sense would say that cells half the length would require half
the space (or double the number of possible elements). Not so.
FWIW, I can define arrays of up to 40,000,000 elements, requiring slightly
more than 500 MB RAM, and about 15 seconds to allocate on a Sun Ultra2.
415 data _null_; stop; run;
NOTE: DATA statement used:
time:
memory:
real 0:00:00.060 page faults 0
user cpu 0:00:00.004 page reclaims 0
system cpu
0:00:00.008 usage 33 K
block I/O operations:
context switches:
input 0 voluntary 5
output 1 involuntary 0
416
417 data _null_;
418
array foo{2000000} $ 8 _temporary_;
419 stop;
420 run;
NOTE: DATA
statement used:
time: memory:
real
0:00:00.940 page faults 0
user cpu 0:00:00.492
page reclaims 0
system cpu 0:00:00.381 usage 30.58
M
block I/O operations: context switches:
input
0 voluntary 7
output 1
involuntary 125
421
422 data _null_;
423 array foo{2000000} $ 4
_temporary_;
424 stop;
425 run;
NOTE: DATA statement used:
time: memory:
real 0:00:01.020
page faults 0
user cpu 0:00:00.510 page reclaims 0
system cpu 0:00:00.376 usage 30.58 M
block I/O
operations: context switches:
input 0
voluntary 8
output 1 involuntary
94
426
427 data _null_;
428 array foo{2000000} $ 16 _temporary_;
429
stop;
430 run;
NOTE: DATA statement used:
time:
memory:
real 0:00:01.260 page faults 0
user cpu 0:00:00.604 page reclaims 0
system cpu
0:00:00.573 usage 45.85 M
block I/O operations:
context switches:
input 0 voluntary 7
output 1 involuntary 145
431
432 data
_null_;
433 array foo{2000000} $ 32 _temporary_;
434 stop;
435
run;
NOTE: DATA statement used:
time:
memory:
real 0:00:01.870 page faults 0
user cpu 0:00:00.771 page reclaims 0
system cpu
0:00:00.981 usage 76.35 M
block I/O operations:
context switches:
input 0 voluntary 7
output 1 involuntary 254
--
Karsten M. Self (Karsten.Self@schwab.com)
Trilogy Consulting
What part of "gestalt" don't you understand?
WARNING: All e-mail sent to or from this address will be received by the
Charles Schwab corporate e-mail system and is subject to archival and
review by someone other than the recipient.
