Feature/transactional commands

.github/workflows/ci.yml

@@ -6,27 +6,110 @@ on:
   pull_request:
     branches: [ "main" ]
 
+# Cancel in-progress runs for the same branch
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
-  build-and-test:
+  # Build job - compiles the project
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 25
+        uses: actions/setup-java@v4
+        with:
+          java-version: '25'
+          distribution: 'temurin'
+          cache: maven
+
+      - name: Build project (skip tests)
+        run: mvn clean compile test-compile -DskipTests -q
+
+      - name: Cache build artifacts
+        uses: actions/cache@v4
+        with:
+          path: target
+          key: ${{ runner.os }}-build-${{ github.sha }}
+
+  # Unit tests job
+  unit-tests:
+    name: Unit Tests
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 25
+        uses: actions/setup-java@v4
+        with:
+          java-version: '25'
+          distribution: 'temurin'
+          cache: maven
+
+      - name: Run unit tests
+        run: mvn test -q
+
+      - name: Upload unit test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: unit-test-results
+          path: target/surefire-reports/
+          retention-days: 7
+
+  # Integration tests job
+  integration-tests:
+    name: Integration Tests
+    needs: build
     runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
+      - name: Set up JDK 25
+        uses: actions/setup-java@v4
+        with:
+          java-version: '25'
+          distribution: 'temurin'
+          cache: maven
+
+      - name: Run integration tests
+        run: mvn verify -DskipUnitTests -q
+
+      - name: Upload integration test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: integration-test-results
+          path: target/failsafe-reports/
+          retention-days: 7
+
+  # Final status check - this job is used for branch protection
+  # All tests must pass for this job to succeed
+  ci-status:
+    name: CI Status Check
+    needs: [build, unit-tests, integration-tests]
+    runs-on: ubuntu-latest
+    if: always()
     steps:
-    - name: Checkout repository
-      uses: actions/checkout@v4
-
-    - name: Set up JDK 25
-      uses: actions/setup-java@v4
-      with:
-        java-version: '25'
-        distribution: 'temurin'
-        cache: maven
-
-    - name: Display Java and Maven version
-      run: |
-        java -version
-        mvn -version
-
-    - name: Build and Run All Tests
-      run: |
-        chmod +x run_all_tests.sh
-        ./run_all_tests.sh
+      - name: Check if all jobs passed
+        run: |
+          if [[ "${{ needs.build.result }}" != "success" ]]; then
+            echo "❌ Build failed"
+            exit 1
+          fi
+          if [[ "${{ needs.unit-tests.result }}" != "success" ]]; then
+            echo "❌ Unit tests failed"
+            exit 1
+          fi
+          if [[ "${{ needs.integration-tests.result }}" != "success" ]]; then
+            echo "❌ Integration tests failed"
+            exit 1
+          fi
+          echo "✅ All checks passed!"

README.md

@@ -14,6 +14,7 @@ A high-performance, lightweight, in-memory Redis-compatible server built from th
 - **💾 In-Memory Storage**: Optimized data structures using `ConcurrentHashMap` for thread-safe, lock-free reads.
 - **🔌 Redis Protocol (RESP)**: Implements the Redis Serialization Protocol, compatible with any standard Redis client (`redis-cli`, `jedis`, `redis-py`, etc.).
 - **⏳ Advanced Expiration**: Dual-strategy expiration (Lazy + Active background cleanup via `DelayQueue`).
+- **🔄 Transaction Support**: Full MULTI/EXEC/DISCARD support with optimized batch execution and zero-contention state management.
 - **🎯 Single-Threaded Execution**: Primarily single-threaded command execution for predictable behavior; blocking commands (e.g., `BLPOP`) are handled asynchronously using Netty's event loop to avoid blocking I/O.
 - **🏗️ Extensible Command Registry**: Easy to add new commands via a simple interface.
 
@@ -38,6 +39,14 @@ Detailed documentation for each command can be found in the [docs/commands](./do
 | `SET` | `SET key value [EX s] [PX ms] [NX\|XX]` | [SET.md](./docs/commands/SET.md) |
 | `GET` | `GET key` | [GET.md](./docs/commands/GET.md) |
 | `DEL` | `DEL key [key ...]` | [DEL.md](./docs/commands/DEL.md) |
+| `INCR` | `INCR key` | [INCR.md](./docs/commands/INCR.md) |
+
+### 🔄 Transactions
+| Command | Usage | Documentation |
+|:---|:---|:---|
+| `MULTI` | `MULTI` | [MULTI.md](./docs/commands/MULTI.md) |
+| `EXEC` | `EXEC` | [EXEC.md](./docs/commands/EXEC.md) |
+| `DISCARD` | `DISCARD` | [DISCARD.md](./docs/commands/DISCARD.md) |
 
 ### 📋 List Operations
 | Command | Usage | Documentation |
@@ -119,10 +128,25 @@ We maintain high confidence through both unit and integration tests.
 
 # Run only unit tests
 mvn test
+
+# Run only integration tests
+mvn verify -DskipUnitTests
 ```
 
 ---
 
+## 🔒 CI/CD & Branch Protection
+
+This repository enforces **mandatory passing tests** before any PR can be merged:
+
+- ✅ **Build** must compile successfully
+- ✅ **Unit Tests** must all pass (469+ tests)
+- ✅ **Integration Tests** must all pass (179+ tests)
+
+The CI pipeline runs automatically on every push and PR. See [Branch Protection Setup](./docs/BRANCH_PROTECTION.md) for configuration details.
+
+---
+
 ## ⚙️ Configuration
 
 Edit `src/main/resources/application.properties`:

docs/commands/DISCARD.md

@@ -0,0 +1,75 @@
+# DISCARD
+
+## Syntax
+
+```
+DISCARD
+```
+
+## Description
+
+Flushes all previously queued commands in a transaction and restores the connection state to normal.
+
+If MULTI was called, DISCARD will abort the transaction. All queued commands are discarded and the client can issue regular commands again.
+
+## Return Value
+
+**Simple string reply:** always `OK`.
+
+## Examples
+
+### Abort a Transaction
+
+```
+redis> SET key "original"
+OK
+redis> MULTI
+OK
+redis> SET key "modified"
+QUEUED
+redis> GET key
+QUEUED
+redis> DISCARD
+OK
+redis> GET key
+"original"
+```
+
+### Start New Transaction After DISCARD
+
+```
+redis> MULTI
+OK
+redis> SET foo bar
+QUEUED
+redis> DISCARD
+OK
+redis> MULTI
+OK
+redis> SET foo baz
+QUEUED
+redis> EXEC
+1) OK
+redis> GET foo
+"baz"
+```
+
+## Error Handling
+
+### DISCARD Without MULTI
+
+```
+redis> DISCARD
+(error) ERR DISCARD without MULTI
+```
+
+## Implementation Notes
+
+### Memory Efficiency
+
+The queued commands list is cleared but not deallocated when DISCARD is called. This allows the memory to be reused if another transaction starts on the same connection, reducing allocation overhead and GC pressure.
+
+## Related Commands
+
+- [MULTI](MULTI.md) - Start a transaction
+- [EXEC](EXEC.md) - Execute all queued commands

docs/commands/EXEC.md

@@ -0,0 +1,113 @@
+# EXEC
+
+## Syntax
+
+```
+EXEC
+```
+
+## Description
+
+Executes all previously queued commands in a MULTI/EXEC block and restores the connection state to normal.
+
+When EXEC is called, all commands queued since MULTI are executed atomically. This means that either all commands are processed, or none are (in case of errors during queueing).
+
+## Return Value
+
+**Array reply:** Each element is the reply from each command in the transaction, in the order they were queued.
+
+**Nil reply:** If EXEC is called without a prior MULTI or if the transaction was aborted due to errors.
+
+## Examples
+
+### Basic Transaction
+
+```
+redis> MULTI
+OK
+redis> SET key1 "Hello"
+QUEUED
+redis> SET key2 "World"
+QUEUED
+redis> GET key1
+QUEUED
+redis> GET key2
+QUEUED
+redis> EXEC
+1) OK
+2) OK
+3) "Hello"
+4) "World"
+```
+
+### Counter Transaction
+
+```
+redis> SET counter 0
+OK
+redis> MULTI
+OK
+redis> INCR counter
+QUEUED
+redis> INCR counter
+QUEUED
+redis> INCR counter
+QUEUED
+redis> GET counter
+QUEUED
+redis> EXEC
+1) (integer) 1
+2) (integer) 2
+3) (integer) 3
+4) "3"
+```
+
+## Error Handling
+
+### EXEC Without MULTI
+
+```
+redis> EXEC
+(error) ERR EXEC without MULTI
+```
+
+### Transaction with Queueing Error
+
+If an error occurs while queueing commands (e.g., syntax error, unknown command), the transaction is aborted:
+
+```
+redis> MULTI
+OK
+redis> SET key value
+QUEUED
+redis> UNKNOWNCOMMAND
+(error) ERR unknown command 'UNKNOWNCOMMAND'
+redis> EXEC
+(error) EXECABORT Transaction discarded because of previous errors.
+```
+
+### Empty Transaction
+
+```
+redis> MULTI
+OK
+redis> EXEC
+(empty array)
+```
+
+## Implementation Notes
+
+### Optimizations Over Standard Redis
+
+1. **Pre-allocated Response Buffer:** The response StringBuilder is pre-sized based on the number of queued commands, minimizing reallocations during execution.
+
+2. **Zero Command Lookups:** Commands are resolved and stored at queue time, not during EXEC. This eliminates registry lookups during the critical execution phase.
+
+3. **Cache-Friendly Iteration:** Commands are stored in a contiguous ArrayList, providing excellent CPU cache utilization during batch execution.
+
+4. **Batch Execution:** All commands execute in a tight loop without intermediate I/O operations, reducing context switches.
+
+## Related Commands
+
+- [MULTI](MULTI.md) - Start a transaction
+- [DISCARD](DISCARD.md) - Abort the transaction