MessageID, which consists of four parts:
MessageID generation rules are determined by Pulsar's message storage mechanism as shown below:
entryId to the file offset will be performed, which will be cached in the memory called "index cache".
LastLogMark marks the position in the journal from where to recover.
LastLogMark is actually stored in the memory. When the index cache is flushed to the disk, its value will be updated. It will also be persisted to the disk periodically for data recovery from the journal when the Bookkeeper process starts.
LastLogMark is persisted to the disk, the preceding index and entry log have been persisted to the disk, and the data in the journal before the
LastLogMark can be cleared.