You can use the substitution functionality in vim to count the number of matches for a given search term like so:
:%s/transaction_id//n
You will see the result in the command tray like so:
8 matches on 8 lines
If you want to find matches globally (that is, counting multiples per line),
you can add the g flag:
:%s/transaction_id//gn
for a response like:
13 matches on 8 lines
The magic is in the n flag which tells vim to report a count of the
matches and not actually perform the substitution. See :h :s_flags for
more details. Also, check out :h count-items.