Prevent concurrent transactions

[devformatters]

Here are flows for preventing concurrent transactions to Postgres:

Couple things to be clarified since flows are in sync style:

• Pending transaction are always returned, which means client side need to revise feedback message. Client get notices when transaction state has been updated.
• Transaction history must includes pending transaction.

Any supplementation to those flows? @robertu7 @guoliu

cc @gyuetong

[devformatters]

To test queue solution, we need stress testing tool. I'm using k6, written in Golang, supports JS scripts to test.

Installation (mac)

brew install k6

Project structure

folder
├── appreciation.js
├── payout.js
├── payto.js
└── shared.js

You can download scripts from here：

• appreciation.js
• payout.js
• payto.js
• shared.js

Run scripts

Please follow the instruction in each scripts to setup, and then run the script with k6. Like this:

k6 run appreciation.js
k6 run payout.js
k6 run payto.js

Verify result

Appreciation

After rounds of execution, you should see each user can only have 5 appreciations to the article.

Payout

After execution, you should see user's HKD balance is always >= 0 by running SQL:

select sum("src"."amount") as "amount" from (
  select
    sum(amount) as amount
  from
    "transaction"
  where
    recipient_id = ${id} and currency = 'HKD' and state = 'succeeded'
  union
  select
    sum((0 - amount)) as amount
  from
    "transaction"
  where
    sender_id = ${id} and currency = 'HKD' and (state = 'succeeded' or state = 'pending')
) as src

and list transactions:

select * from "transaction" where "sender_id" = ${id} or "recipient_id" = ${id} order by created_at desc

Pay-to

After running script, you should see users's HKD balance is always >= 0, and transactions might be succeeded or canceled by running SQL queries above.

[guoliu]

Implemented with #1115 and #1165