Kindly help on follows.

I have 2 files. One file contains only one column of mobile numbers. And total records in a file 12 million. Second file contains 2 columns mobile numbers and balance. and total records 30 million. I want to find out balance of each data in file 1 corresponding to file 2. I tried egrep -f but it will take very long time. And also use awk '{OFS="|"}NR<=FNR{a[$1]=$1}NR>FNR{print $1,$2,a[$1]}' a b but its given error after 7 million says long data. Can you provide me other commands. please

Thanks in advance..