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.