Merge pull request codecrafters-io#226 from codecrafters-io/add-transactions-docs

Add support for multiple concurrent transactions in stage "Multiple transactions".

Author: rohitpaulk

course-definition.yml

@@ -3712,7 +3712,53 @@ stages:
     name: "Multiple transactions"
     difficulty: medium
     description_md: |
-      **🚧 We're still working on instructions for this stage**. You can find notes on how the tester works below.
+      In this stage, you'll add support for multiple concurrent transactions.
+
+      ### Multiple transactions
+
+      There can be multiple transactions open (i.e. `MULTI` has been called, but `EXEC` has not been called yet) at the same time. Each
+      transaction gets its own command queue.
+
+      For example, say you started transaction 1 from one connection:
+
+      ```bash
+      $ redis-cli
+      > MULTI
+      OK
+      > SET foo 41
+      QUEUED
+      > INCR foo
+      QUEUED
+      ```
+
+      and started transaction 2 from another connection:
+
+      ```bash
+      $ redis-cli
+      > MULTI
+      OK
+      > INCR foo
+      QUEUED
+      ```
+
+      If you then run `EXEC` in transaction 1, you should see the following:
+
+      ```bash
+      > EXEC
+      1) OK
+      2) (integer) 42
+      ```
+
+      `OK` is the response to `SET foo 41`, and `42` is the response to `INCR foo`.
+
+      And for transaction 2, running `EXEC` should return:
+
+      ```bash
+      > EXEC
+      1) (integer) 43
+      ```
+
+      43 is the response to `INCR foo`. The key `foo` was updated to `42` by transaction 1, and `INCR foo` further increments it to `43`.
 
       ### Tests