f61e1dd2ce
Prior to this patch, when running pg_receivewal, the streaming start point would be the current location of the archives if anything is found in the local directory where WAL segments are written, and pg_receivewal would fall back to the current WAL flush location if there are no archives, as of the result of an IDENTIFY_SYSTEM command. If for some reason the WAL files from pg_receivewal were moved, it is better to try a restart where we left at, which is the replication slot's restart_lsn instead of skipping right to the current flush location, to avoid holes in the WAL backed up. This commit changes pg_receivewal to use the following sequence of methods to determine the starting streaming LSN: - Scan the local archives. - Use the slot's restart_lsn, if supported by the backend and if a slot is defined. - Fallback to the current flush LSN as reported by IDENTIFY_SYSTEM. To keep compatibility with older server versions, we only attempt to use READ_REPLICATION_SLOT if the backend version is at least 15, and fallback to the older behavior of streaming from the current flush LSN if the command is not supported. Some TAP tests are added to cover this feature. Author: Ronan Dunklau Reviewed-by: Kyotaro Horiguchi, Michael Paquier, Bharath Rupireddy Discussion: https://postgr.es/m/18708360.4lzOvYHigE@aivenronan
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