FWIW, here is a tacobell solution:

$uname -a
Linux o-test-server 3.19.0-25-generic #26~14.04.1-Ubuntu SMP Fri Jul 24 21:16:20 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

$sudo apt install tinycdb

$tr -cd '[:alnum:]' < /dev/urandom | fold -w8 | head -n100000000 > test.txt

$cut -c1-4 test.txt > test2.txt

$paste test.txt test2.txt > test3.txt

$cdb -c -m test3.cdb test3.txt

$ cdb -q test.cdb 2Jaj8gGM
2Jaj

$ls -lh test3.*
-rw-rw-r-- 1 od user 3.4G Jun  3 11:14 test3.cdb
-rw-rw-r-- 1 od user 1.4G Jun  3 11:08 test3.txt