@@ -15,7 +15,7 @@ The message storage architecture diagram consists of 3 files related to message
*`CommitLog`：The `CommitLog` file stores message body and metadata sent by producer, and the message content is not fixed length. The default size of one `CommitLog` file is 1G, the length of the file name is 20 digits, the left side is zero padded, and the remaining is the starting offset. For example, `00000000000000000000` represents the first file, the starting offset is 0, and the file size is 1G=1073741824, when the first `CommitLog` file is full, the second `CommitLog` file is `00000000001073741824`, the starting offset is 1073741824, and so on. The message is mainly appended to the log file sequentially. When one `CommitLog` file is full, the next will be written.
*`ConsumeQueue`: The `ConsumeQueue` is used to improve the performance of message consumption. Since RocketMQ uses topic-based subscription mode, message consumption is specific to the topic. Traversing the commitlog file to retrieve messages of one topic is very inefficient. The consumer can find the messages to be consumed according to the `ConsumeQueue`. The `ConsumeQueue`(logic consume queue) as an index of the consuming message stores the starting physical offset `offset` in `CommitLog` of the specified topic, the message size `size` and the hash code of the message tag. The `ConsumeQueue` file can be regarded as a topic-based `CommitLog` index file, so the consumequeue folder is organized as follows: `topic/queue/file` three-layer organization structure, the specific storage path is `$HOME/store/consumequeue/{topic}/{queueId }/{fileName}`. The consumequeue file uses a fixed-length design, each entry occupies 20 bytes, which is an 8-byte commitlog physical offset, a 4-byte message length, and an 8-byte tag hashcode. One consumequeue file consists of 30W entries, each entry can be randomly accessed like an array, each `ConsumeQueue` file's size is about 5.72M.
*`ConsumeQueue`: The `ConsumeQueue` is used to improve the performance of message consumption. Since RocketMQ uses topic-based subscription mode, message consumption is specific to the topic. Traversing the commitlog file to retrieve messages of one topic is very inefficient. The consumer can find the messages to be consumed according to the `ConsumeQueue`. The `ConsumeQueue`(logic consume queue) as an index of the consuming message stores the starting physical offset `offset` in `CommitLog` of the specified topic, the message size `size` and the hash code of the message tag. The `ConsumeQueue` file can be regarded as a topic-based `CommitLog` index file, so the consumequeue folder is organized as follows: `topic/queue/file` three-layer organization structure, the specific storage path is `$HOME/store/consumequeue/{topic}/{queueId }/{fileName}`. The consumequeue file uses a fixed-length design, each entry occupies 20 bytes, which is an 8-byte commitlog physical offset, a 4-byte message length, and an 8-byte tag hashcode. One consumequeue file consists of 0.3 million entries, each entry can be randomly accessed like an array, each `ConsumeQueue` file's size is about 5.72MB.
*`IndexFile`: The `IndexFile` provides a way to query messages by key or time interval. The path of the `IndexFile` is `$HOME/store/index/${fileName}`, the file name `fileName` is named after the timestamp when it was created. One IndexFile's size is about 400M, and it can store 2000W indexes. The underlying storage of `IndexFile` is designed to implement the `HashMap` structure in the file system, so RocketMQ's index file is a hash index.
