Voucher

Just a demonstration project

How to build

./gradlew clean
./gradlew build

How to run web project

./gradlew bootrun

How to access H2 database console

Open browser at http://localhost:8080/h2-console. Login using credentials username demo, password demo.

Objective to this demonstration

It is to demonstrate how to use Pessimistic lock on a locking table to achieve consistent testing of number of records before insertion in an atomic transactional manner

How to test

1. Start up the web application. Refer to How to run web project.
2. Open the browser and login to the h2 database console.
3. Select all rows from the voucher table. It should shows empty rows.
4. Using a terminal shell, run the following codes:

   for i in `seq 1 1000`; do
     curl -s http://localhost:8080/voucher/request?userid=$[ $RANDOM % 100 ] >/dev/null &
   done

   This will ensure there are 1000 concurrent processes trying to obtain vouchers from the system.
5. Once step (4) is done, use the h2 database console, run the following query to find out the number of vouchers requested for each user.

   select user_id, count(*) from voucher group by user_id;

   It should shows that each user(user_id) should have at most 2 vouchers issued.