Beyond the limits - environment (cont 2)

Comment from Paul for the article make me rerun the tests in different conditions: I update the memory of both machines to 1024 MB and use scripts (see below)

[root@centos ~]# cat z1.sh
TEMPVAR=A
for i in {1..1000};
        do
        TEMPVAR=${TEMPVAR}$TEMPVAR;
        a=$(echo 2^$i|bc)
        b=${#TEMPVAR}
        if [ $a -ne $b ]
        then echo KO - $a, $b
        else echo $a
        fi
done
[root@centos ~]# cat z1.1.sh
TEMPVAR=A
for i in {1..1000};
        do
        TEMPVAR=${TEMPVAR}$TEMPVAR;
        a=$(echo 2^$i+1|bc)
        b=$(echo $TEMPVAR|wc -c)
        if [ $a -ne $b ]
        then echo KO - $a, $b
        else echo $a
        fi
done

Solaris
On Solaris independently of the amout of memory and the way of get length of environment variable the result is same:

bash-3.00# vmstat 1 2
 kthr      memory            page            disk          faults      cpu
 r b w   swap  free  re  mf pi po fr de sr cd f0 s0 --   in   sy   cs us sy id
 0 0 0 1075080 616428 152 3085 0 0 0  0 204 10 -0 3  0  309 3345 1511 14 19 67
 1 0 0 1407772 753456 18 50  0  0  0  0  0  0  0  0  0  304  324  142  0  1 99

It seems 32MB is internal limitation in bash (or OS) in Solaris

bash-3.00# ./z1.sh
2
4
<snip>
8388608
16777216
33554432
./z1.sh: fork: Not enough space
./z1.sh: line 7: [: -ne: unary operator expected
./z1.sh: fork: Not enough space
bash-3.00# ./z1.1.sh
3
5
<snip>
16777217
33554433
./z1.1.sh: fork: Not enough space
./z1.1.sh: fork: Not enough space
KO - ,
./z1.1.sh: fork: Not enough space

And the execution times follow the common sense

bash-3.00# time ./z1.sh
2
4
<snip>
16777216
33554432
real    0m9.670s
user    0m6.454s
sys     0m3.014s
bash-3.00# time ./z1.1.sh
3
5
<snip>
16777217
33554433
real    0m13.709s
user    0m8.040s
sys     0m5.352s


Linux
But on linux

[root@centos ~]# vmstat 1 2
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0  10416 1016704    252   4072   75  804   318   828 1008   77 19 44 32  4  0
 0  0  10416 1016704    252   4096    0    0     0     0 1015   14  0  1 99  0  0


my method of count permit me to reach bigger length

[root@centos ~]# ./z1.sh
2
4
<snip>
67108864
134217728
./z1.sh: xmalloc: cannot allocate 536870913 bytes (0 bytes allocated)
[root@centos ~]# ./z1.1.sh
3
5
<snip>
134217729
268435457
./z1.1.sh: xmalloc: cannot allocate 1073741825 bytes (0 bytes allocated)
KO - 536870913, 0
./z1.1.sh: xmalloc: cannot allocate 1073741825 bytes (0 bytes allocated)
 

and need less execution time (with limit to 2^26)

[root@centos ~]# time ./z1.sh
2
4
<snip>
33554432
67108864
real    1m58.730s
user    0m33.084s
sys     1m27.562s
[root@centos ~]# time ./z1.1.sh
3
5
<snip>
33554433
67108865
real    1m36.457s
user    0m50.206s
sys     0m47.815s



Final conclusion: this need further investigations :)