This code:

   foreach $uniquekey1 (keys %myHash1)
        {
               $uniq2 = $file_name1.'.csv';
            sysopen($CircleGroupHandle1,"$ARGV[0]/$uniq2",O_WRONLY|
+O_APPEND|O_CREAT)or die "Error writing to $!";
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If you look closely the file name is composed of: "$ARGV[0]/$file_name1.csv", all of the variables involved are defined outside the foreach loop, if that doesn't change that means that within the loop you're opening the same file over and over.

The first optimization would be to extra the constants from the loop.< That means that $file_name and the file_handle can be outside the foreach loop. This will prevent your program to open same file multiple times ( one per keys in %myHash ). Let's say %myHash has 10k keys, that means you opening ( without closing ) same file 10k times.

here u will get the idea wht i am trying to do file name: abc_def_hij.csv data on any line comma seperated as: aaa,abc,aaa,def,aaa,hij…….. etc data on another line comma seperated: xxx,abc,xxx,def,xxx,hij..... etc. now another source file may contain data as coma seperated as : bbb,abc,bbb,def,bbb,hij .... etc so the data from another file should got appended in abc_def_hij.csv file. i will be g8t full if u solve this another thing if i exclude strict & warning every thing is working fine but it is taking app 5min to read 1 million records to create such files from it

Can you post your new code.

Also you said it takes 5 minutes to process 1M records, so what is your expected mark?