05 янв. 2015 г., в 18:15, Vladimir Borodin <r...@simply.name> написал(а):
> Hi all. > > I have a simple script for planned switchover of PostgreSQL (9.3 and 9.4) > master to one of its replicas. This script checks a lot of things before > doing it and one of them is that all data from master has been received by > replica that is going to be promoted. Right now the check is done like below: > > On the master: > > postgres@pgtest03d ~ $ psql -t -A -c 'select pg_current_xlog_location();' > 0/33000090 > postgres@pgtest03d ~ $ /usr/pgsql-9.3/bin/pg_ctl stop -m fast > waiting for server to shut down.... done > server stopped > postgres@pgtest03d ~ $ /usr/pgsql-9.3/bin/pg_controldata | head > pg_control version number: 937 > Catalog version number: 201306121 > Database system identifier: 6061800518091528182 > Database cluster state: shut down > pg_control last modified: Mon 05 Jan 2015 06:47:57 PM MSK > Latest checkpoint location: 0/34000028 > Prior checkpoint location: 0/33000028 > Latest checkpoint's REDO location: 0/34000028 > Latest checkpoint's REDO WAL file: 0000001B0000000000000034 > Latest checkpoint's TimeLineID: 27 > postgres@pgtest03d ~ $ > > On the replica (after shutdown of master): > > postgres@pgtest03g ~ $ psql -t -A -c "select > pg_xlog_location_diff(pg_last_xlog_replay_location(), '0/34000028');" > 104 > postgres@pgtest03g ~ $ > > These 104 bytes seems to be the size of shutdown checkpoint record (as I can > understand from pg_xlogdump output). > > postgres@pgtest03g ~/9.3/data/pg_xlog $ /usr/pgsql-9.3/bin/pg_xlogdump -s > 0/33000090 -t 27 > rmgr: XLOG len (rec/tot): 0/ 32, tx: 0, lsn: > 0/33000090, prev 0/33000028, bkp: 0000, desc: xlog switch > rmgr: XLOG len (rec/tot): 72/ 104, tx: 0, lsn: > 0/34000028, prev 0/33000090, bkp: 0000, desc: checkpoint: redo 0/34000028; > tli 27; prev tli 27; fpw true; xid 0/6010; oid 54128; multi 1; offset 0; > oldest xid 1799 in DB 1; oldest multi 1 in DB 1; oldest running xid 0; > shutdown > pg_xlogdump: FATAL: error in WAL record at 0/34000028: record with zero > length at 0/34000090 > > postgres@pgtest03g ~/9.3/data/pg_xlog $ > > I’m not sure that these 104 bytes will always be 104 bytes to have a strict > equality while checking. Could it change in the future? Or is there a better > way to understand that streaming replica received all data after master > shutdown? The check that pg_xlog_location_diff returns 104 bytes seems a bit > strange. > +hackers Could anyone help? Thanks. > Thanks. > > -- > May the force be with you... > http://simply.name > > > > -- May the force be with you... http://simply.name
