I started trying to debug backup with minimal WALs for achieve consistency, it is from 'server 2' and it only needs 20 WAL files. It error was: ERROR: xlog flush request 44B/7E5DAB28 is not satisfied --- flushed only to 44B/7305B560 CONTEXT: writing block 0 of relation base/16506/16891_vm === backup_label === START WAL LOCATION: 44B/6002F280 (file 000000010000044B00000060) CHECKPOINT LOCATION: 44B/7305B4F0 BACKUP METHOD: streamed BACKUP FROM: standby START TIME: 2019-02-13 03:19:54 MSK LABEL: pg_basebackup base backup === controldata === Database cluster state: in archive recovery pg_control last modified: Wed 13 Feb 2019 03:19:54 AM MSK Latest checkpoint location: 44B/7305B4F0 Latest checkpoint's REDO location: 44B/6002F280 Latest checkpoint's REDO WAL file: 000000010000044B00000060 Time of latest checkpoint: Wed 13 Feb 2019 02:19:36 AM MSK Minimum recovery ending location: 44B/7305B560 I scan all *_vm files in DB 16506 for pages with LSN bigger than 'Minimum recovery ending location' and find three files: base/16506/190024_vm 0000000 44B/9411F5C0 base/16506/190005_vm 0000000 44B/94121DE8 base/16506/16891_vm 0000000 44B/7E5DAB28 Then I parse (pg_xlogdump) all this 20 WALs, needed for consistency and search for this three oid, for 190024 and 190005 I found VISIBLE WAL record: === $ grep 190024 wals-text | grep VISIBLE === rmgr: Heap2 len (rec/tot): 64/ 8256, tx: 0, lsn: 44B/651EDAE8, prev 44B/651EDA58, desc: VISIBLE cutoff xid 752732359 flags 1, blkref #0: rel 1663/16506/190024 fork vm blk 0 FPW, blkref #1: rel 1663/16506/190024 blk 0 rmgr: Heap2 len (rec/tot): 59/ 59, tx: 0, lsn: 44B/6B19A6E8, prev 44B/6B19A658, desc: VISIBLE cutoff xid 752734764 flags 1, blkref #0: rel 1663/16506/190024 fork vm blk 0, blkref #1: rel 1663/16506/190024 blk 0 rmgr: Heap2 len (rec/tot): 59/ 59, tx: 0, lsn: 44B/71194D40, prev 44B/71194CB0, desc: VISIBLE cutoff xid 752737874 flags 1, blkref #0: rel 1663/16506/190024 fork vm blk 0, blkref #1: rel 1663/16506/190024 blk 0 === $ grep 190005 wals-text | grep VISIBLE === rmgr: Heap2 len (rec/tot): 64/ 8256, tx: 0, lsn: 44B/651F3728, prev 44B/651F36C8, desc: VISIBLE cutoff xid 752732355 flags 1, blkref #0: rel 1663/16506/190005 fork vm blk 0 FPW, blkref #1: rel 1663/16506/190005 blk 0 rmgr: Heap2 len (rec/tot): 59/ 59, tx: 0, lsn: 44B/6B19AE80, prev 44B/6B19AE20, desc: VISIBLE cutoff xid 752732667 flags 1, blkref #0: rel 1663/16506/190005 fork vm blk 0, blkref #1: rel 1663/16506/190005 blk 0 rmgr: Heap2 len (rec/tot): 59/ 59, tx: 0, lsn: 44B/6B19CF10, prev 44B/6B19AEC0, desc: VISIBLE cutoff xid 752734752 flags 1, blkref #0: rel 1663/16506/190005 fork vm blk 0, blkref #1: rel 1663/16506/190005 blk 1 rmgr: Heap2 len (rec/tot): 59/ 59, tx: 0, lsn: 44B/711954D8, prev 44B/71195478, desc: VISIBLE cutoff xid 752737869 flags 1, blkref #0: rel 1663/16506/190005 fork vm blk 0, blkref #1: rel 1663/16506/190005 blk 0 But I did not find in parsed WALs anything about vm fork for 16891. Is it OK, or is something wrong here? PS: I try to remove all problematic visibility maps, with page LSN bigger than 'Minimum recovery ending location') and start backup without it. Without it postgres started successfully. -- Sergey Burladyan
