Discontinuous append queue file sequnce

[v0y4g3r]

Accidentally I found that raft-engine's data directory contains discontinuous file sequences in append queue:

0000000000000003.rewrite
0000000000000846.raftlog
0000000000000847.raftlog
0000000000000848.raftlog
0000000000000849.raftlog
0000000000000850.raftlog
0000000000000851.raftlog
0000000000000852.raftlog
0000000000000853.raftlog
0000000000000854.raftlog
0000000000000855.raftlog
0000000000000856.raftlog
0000000000000857.raftlog
0000000000000858.raftlog
0000000000000859.raftlog
0000000000000860.raftlog < here
0000000000000890.raftlog

During raft-engine's recover process, all files before 0000000000000890 in append queue will be skipped. I am curious if such a situation would occur in normal program operation as when I dive into the purge code: https://github.com/tikv/raft-engine/blob/e8de5d75ae40b0eec8736321f9dedb1662feb69d/src/file_pipe_log/pipe.rs#L426

Looks like in purge_to method normally all files before file_seq are either all deleted or not.

[tabokie]

I think it's caused by file recycling (SinglePipe::recycled_files), some of obsolete log files will be kept around for future writes to reuse. After https://github.com/tikv/raft-engine/pull/310, those files no longer use a different file extension, so you can't distinguish them based on file name alone.

[v0y4g3r]

I think it's caused by file recycling (SinglePipe::recycled_files), some of obsolete log files will be kept around for future writes to reuse. After #310, those files no longer use a different file extension, so you can't distinguish them based on file name alone.

Log recycle is not enabled yet, could it be any other reason?

[tabokie]

Did you disable it explicitly? It is enabled by default for a while now.