[Bug] First log has no records when target-file-size < LogFileFormat::encoded_len()

[LykxSassinator]

Referring to pr: #269, after we refactored the sync, we found that the first log (file_seq == 1) is always empty when setting target-file-size < LogFileFormat::encoded_len().

The root cause is that we will check whether to do rotate before each real write, in the processing of append.

raft-engine/src/file_pipe_log/pipe.rs

Lines 355 to 356 in 618eea7

	if active_file.writer.offset() >= self.target_file_size {
	if let Err(e) = self.rotate_imp(&mut active_file) {

And if we set target-file-size with a abnormal value, such as 1, the startup of Pipe will automatically generate the first seq file with sequence number 1. Any append to this Pipe will not be added to the first file, which will be added to the next seq file, file_seq == 2.

[tabokie]

It's not a bug. You can switch the order (between write and rotate) if it makes testing easier.