+ /* + * Perform a full directory scan to identify the next log segment. There + * may be one of the following scenarios which may require us to perform a + * full directory scan. + * + * 1. This is the first cycle since archiver has started and there is no + * idea about the next anticipated log segment. + * + * 2. There is a timeline switch, i.e. the timeline ID tracked at archiver + * does not match with current timeline ID. Archive history file as part of + * this timeline switch. + * + * 3. The next anticipated log segment is not available.
One benefit of the current implementation of pgarch_readyXlog() is that .ready files created out of order will be prioritized before segments with greater LSNs. IIUC, with this patch, as long as there is a "next anticipated" segment available, the archiver won't go back and archive segments it missed. I don't think the archive status files are regularly created out of order, but XLogArchiveCheckDone() has handling for that case, and the work to avoid creating .ready files too early [0] seems to make it more likely. Perhaps we should also force a directory scan when we detect that we are creating a .ready file for a segment that is older than the "next anticipated" segment. Nathan [0] https://postgr.es/m/DA71434B-7340-4984-9B91-F085BC47A778%40amazon.com
