273 lines
9.4 KiB
Markdown
273 lines
9.4 KiB
Markdown
该文所涉及的 RocketMQ 源码版本为 4.9.3。
|
||
|
||
# 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);
|
||
}
|
||
}
|
||
}
|
||
```
|