feat: add commitLog detail (#114)

* add CommitLog detail

README.md

@@ -279,6 +279,7 @@
 - [RocketMQ 消息发送存储流程](docs/rocketmq/rocketmq-send-store.md)
 - [RocketMQ MappedFile内存映射文件详解](docs/rocketmq/rocketmq-mappedfile-detail.md)
 - [RocketMQ ConsumeQueue详解](docs/rocketmq/rocketmq-consumequeue.md)
+- [RocketMQ CommitLog详解](docs/rocketmq/rocketmq-commitlog.md)
 
 ## 番外篇（JDK 1.8）
 

docs/rocketmq/rocketmq-commitlog.md

@@ -0,0 +1,270 @@
+# RocketMQ CommitLog 详解
+
+commitlog 目录主要存储消息，为了保证性能，顺序写入，每一条消息的长度都不相同，每条消息的前面四个字节存储该条消息的总长度，每个文件大小默认为 1G，文件的命名是以 commitLog 起始偏移量命名的，可以通过修改 broker 配置文件中 mappedFileSizeCommitLog 属性改变文件大小
+
+1、获取最小偏移量
+
+org.apache.rocketmq.store.CommitLog#getMinOffset
+
+```java
+public long getMinOffset() {
+    MappedFile mappedFile = this.mappedFileQueue.getFirstMappedFile();
+    if (mappedFile != null) {
+        if (mappedFile.isAvailable()) {
+            return mappedFile.getFileFromOffset();
+        } else {
+            return this.rollNextFile(mappedFile.getFileFromOffset());
+        }
+    }
+
+    return -1;
+}
+```
+
+获取目录下的第一个文件
+
+```java
+public MappedFile getFirstMappedFile() {
+    MappedFile mappedFileFirst = null;
+
+    if (!this.mappedFiles.isEmpty()) {
+        try {
+            mappedFileFirst = this.mappedFiles.get(0);
+        } catch (IndexOutOfBoundsException e) {
+            //ignore
+        } catch (Exception e) {
+            log.error("getFirstMappedFile has exception.", e);
+        }
+    }
+
+    return mappedFileFirst;
+}
+```
+
+如果该文件可用返回文件的起始偏移量,否则返回下一个文件的 起始偏移量
+
+```java
+public long rollNextFile(final long offset) {
+    int mappedFileSize = this.defaultMessageStore.getMessageStoreConfig().getMappedFileSizeCommitLog();
+    return offset + mappedFileSize - offset % mappedFileSize;
+}
+```
+
+2、根据偏移量和消息长度查找消息
+
+org.apache.rocketmq.store.CommitLog#getMessage
+
+```java
+public SelectMappedBufferResult getMessage(final long offset, final int size) {
+    int mappedFileSize = this.defaultMessageStore.getMessageStoreConfig().getMappedFileSizeCommitLog();
+    MappedFile mappedFile = this.mappedFileQueue.findMappedFileByOffset(offset, offset == 0);
+    if (mappedFile != null) {
+        int pos = (int) (offset % mappedFileSize);
+        return mappedFile.selectMappedBuffer(pos, size);
+    }
+    return null;
+}
+```
+
+首先获取 commitLog 文件大小,默认 1G
+
+`private int mappedFileSizeCommitLog = 1024 * 1024 * 1024;`
+
+获取偏移量所在的 MappedFile
+
+org.apache.rocketmq.store.MappedFileQueue#findMappedFileByOffset(long, boolean)
+
+获取第一个 MappedFile 和最后一个 MappedFile，校验偏移量是否在这两个 MappedFile 之间,计算当前偏移量所在 MappedFiles 索引值为当前偏移量的索引减去第一个文件的索引值
+
+```java
+if (firstMappedFile != null && lastMappedFile != null) {
+    if (offset < firstMappedFile.getFileFromOffset() || offset >= lastMappedFile.getFileFromOffset() + this.mappedFileSize) {
+        LOG_ERROR.warn("Offset not matched. Request offset: {}, firstOffset: {}, lastOffset: {}, mappedFileSize: {}, mappedFiles count: {}",
+            offset,
+            firstMappedFile.getFileFromOffset(),
+            lastMappedFile.getFileFromOffset() + this.mappedFileSize,
+            this.mappedFileSize,
+            this.mappedFiles.size());
+    } else {
+        int index = (int) ((offset / this.mappedFileSize) - (firstMappedFile.getFileFromOffset() / this.mappedFileSize));
+        MappedFile targetFile = null;
+        try {
+            targetFile = this.mappedFiles.get(index);
+        } catch (Exception ignored) {
+        }
+
+        if (targetFile != null && offset >= targetFile.getFileFromOffset()
+            && offset < targetFile.getFileFromOffset() + this.mappedFileSize) {
+            return targetFile;
+        }
+
+        for (MappedFile tmpMappedFile : this.mappedFiles) {
+            if (offset >= tmpMappedFile.getFileFromOffset()
+                && offset < tmpMappedFile.getFileFromOffset() + this.mappedFileSize) {
+                return tmpMappedFile;
+            }
+        }
+    }
+
+    if (returnFirstOnNotFound) {
+        return firstMappedFile;
+    }
+}
+```
+
+根据在文件内的偏移量和消息长度获取消息内容
+
+```java
+public SelectMappedBufferResult selectMappedBuffer(int pos, int size) {
+    int readPosition = getReadPosition();
+    if ((pos + size) <= readPosition) {
+        if (this.hold()) {
+            ByteBuffer byteBuffer = this.mappedByteBuffer.slice();
+            byteBuffer.position(pos);
+            ByteBuffer byteBufferNew = byteBuffer.slice();
+            byteBufferNew.limit(size);
+            return new SelectMappedBufferResult(this.fileFromOffset + pos, byteBufferNew, size, this);
+        } else {
+            log.warn("matched, but hold failed, request pos: " + pos + ", fileFromOffset: "
+                + this.fileFromOffset);
+        }
+    } else {
+        log.warn("selectMappedBuffer request pos invalid, request pos: " + pos + ", size: " + size
+            + ", fileFromOffset: " + this.fileFromOffset);
+    }
+
+    return null;
+}
+```
+
+3、Broker 正常停止文件恢复
+
+org.apache.rocketmq.store.CommitLog#recoverNormally
+
+首先查询消息是否验证 CRC
+
+`boolean checkCRCOnRecover = this.defaultMessageStore.getMessageStoreConfig().isCheckCRCOnRecover();`
+
+从倒数第 3 个文件开始恢复，如果不足 3 个文件，则从第一个文件开始恢复
+
+```java
+int index = mappedFiles.size() - 3;
+if (index < 0)
+    index = 0;
+```
+
+循环遍历 CommitLog 文件，每次取出一条消息
+
+`DispatchRequest dispatchRequest = this.checkMessageAndReturnSize(byteBuffer, checkCRCOnRecover);`
+
+如果查找结果为 true 并且消息的长度大于 0，表示消息正确，mappedFileOffset 指针向前移动本条消息的长度；
+
+```java
+if (dispatchRequest.isSuccess() && size > 0) {
+    mappedFileOffset += size;
+}
+```
+
+如果查找结果为 true 并且结果等于 0，表示已到文件 的末尾，如果还有下一个文件，则重置 processOffset、mappedOffset 并重复上述步骤，否则跳出循环；
+
+```java
+else if (dispatchRequest.isSuccess() && size == 0) {
+    index++;
+    if (index >= mappedFiles.size()) {
+        // Current branch can not happen
+        log.info("recover last 3 physics file over, last mapped file " + mappedFile.getFileName());
+        break;
+    } else {
+        mappedFile = mappedFiles.get(index);
+        byteBuffer = mappedFile.sliceByteBuffer();
+        processOffset = mappedFile.getFileFromOffset();
+        mappedFileOffset = 0;
+        log.info("recover next physics file, " + mappedFile.getFileName());
+    }
+}
+```
+
+如果查找结果为 false，则表示消息没有填满该文件，跳出循环，结束遍历
+
+```java
+else if (!dispatchRequest.isSuccess()) {
+    log.info("recover physics file end, " + mappedFile.getFileName());
+    break;
+}
+```
+
+更新 committedPosition 和 flushedWhere 指针
+
+```java
+this.mappedFileQueue.setFlushedWhere(processOffset);
+this.mappedFileQueue.setCommittedWhere(processOffset);
+```
+
+删除 offset 之后的所有文件。遍历目录下面的所有文件，如果文件尾部偏移量小于 offset 则跳过该文件，如果尾部的偏移量大于 offset，则进一步比较 offset 与文件的开始偏移量，如果 offset 大于文件的开始偏移量，说明当前文件包含了有效偏移量，设置 MappedFile 的 flushPosition 和 commitedPosition。
+
+如果 offset 小于文件的开始偏移量，说明该文件是有效文件后面创建的，调用 MappedFile#destroy()方法释放资源
+
+```java
+if (fileTailOffset > offset) {
+    if (offset >= file.getFileFromOffset()) {
+        file.setWrotePosition((int) (offset % this.mappedFileSize));
+        file.setCommittedPosition((int) (offset % this.mappedFileSize));
+        file.setFlushedPosition((int) (offset % this.mappedFileSize));
+    } else {
+        file.destroy(1000);
+        willRemoveFiles.add(file);
+    }
+}
+```
+
+释放资源需要关闭 MappedFile 和文件通道 fileChannel
+
+```java
+public boolean destroy(final long intervalForcibly) {
+    this.shutdown(intervalForcibly);
+
+    if (this.isCleanupOver()) {
+        try {
+            this.fileChannel.close();
+            log.info("close file channel " + this.fileName + " OK");
+
+            long beginTime = System.currentTimeMillis();
+            boolean result = this.file.delete();
+            log.info("delete file[REF:" + this.getRefCount() + "] " + this.fileName
+                + (result ? " OK, " : " Failed, ") + "W:" + this.getWrotePosition() + " M:"
+                + this.getFlushedPosition() + ", "
+                + UtilAll.computeElapsedTimeMilliseconds(beginTime));
+        } catch (Exception e) {
+            log.warn("close file channel " + this.fileName + " Failed. ", e);
+        }
+
+        return true;
+    } else {
+        log.warn("destroy mapped file[REF:" + this.getRefCount() + "] " + this.fileName
+            + " Failed. cleanupOver: " + this.cleanupOver);
+    }
+
+    return false;
+}
+```
+
+判断`maxPhyOffsetOfConsumeQueue`是否大于 processOffset，如果大于，需要删除 ConsumeQueue 中 processOffset 之后的数据
+
+```java
+if (maxPhyOffsetOfConsumeQueue >= processOffset) {
+    log.warn("maxPhyOffsetOfConsumeQueue({}) >= processOffset({}), truncate dirty logic files", maxPhyOffsetOfConsumeQueue, processOffset);
+    this.defaultMessageStore.truncateDirtyLogicFiles(processOffset);
+}
+```
+
+```java
+public void truncateDirtyLogicFiles(long phyOffset) {
+    ConcurrentMap<String, ConcurrentMap<Integer, ConsumeQueue>> tables = DefaultMessageStore.this.consumeQueueTable;
+
+    for (ConcurrentMap<Integer, ConsumeQueue> maps : tables.values()) {
+        for (ConsumeQueue logic : maps.values()) {
+            logic.truncateDirtyLogicFiles(phyOffset);
+        }
+    }
+}
+```