Wanting a nice test of restartable recovery and pg_standby in a warm standby server scenario I'm testing, today I pulled the plug on the box where I was using Simon's test_warm_standby test harness. Basically, in this scenario, I had one posgres cluster (primary) against which pgbench was being run and a separate cluster (standby) that had been created from a base backup and then put into continuous recovery using pg_standby. In the middle of this scenario, I literally pulled the plug. When the box came back up, I restarted primary. Everything came up fine. Then I restarted secondary. Here's what I got: Trigger file : /tmp/pgsql.trigger.5442 Waiting for WAL file : ../archive/00000001000000000000000E WAL file path : 00000001000000000000000E Restoring to... : pg_xlog/RECOVERYXLOG Sleep interval : 5 seconds Max wait interval : 0 forever Command for restore : cp ../archive/00000001000000000000000E pg_xlog/RECOVER YXLOG Num archived files kept : all files WAL file not present yet. Checking for trigger file... WAL file not present yet. Checking for trigger file... WAL file not present yet. Checking for trigger file... WAL file not present yet. Checking for trigger file... ... So something seems to have misfired in pg_standby. I'm having a hard time telling what might have hung it up. I wound up recovering by touching the trigger file, and standby came up as a running postgres server, but it was behind, probably as far as 00000001000000000000000E. The curious part is that all the files were in the archive, so what state would pulling the plug have set that pg_standby either interpreted incorrectly or failed to interpret? When I tested a lighter weight version of this scenario merely by killing standby from the command line and then restarting it, it did this: Trigger file : /tmp/pgsql.trigger.5442 Waiting for WAL file : ../archive/00000001.history WAL file path : 00000001.history Restoring to... : pg_xlog/RECOVERYHISTORY Sleep interval : 5 seconds Max wait interval : 0 forever Command for restore : cp ../archive/00000001.history pg_xlog/RECOVERYHISTORY Num archived files kept : all files running restore :cp: cannot access ../archive/00000001.history cp: cannot access ../archive/00000001.history cp: cannot access ../archive/00000001.history not restored : history file not found But then it got back in the game and continued the continuous recovery process. I was able then to complete final recovery, and it seemed caught up. If anyone can shed light on what might've happened in the hard failure scenario, I'd be interested to know. I've kept the various archive, primary, and standby directories created by test_warm_standby, so I can report on any file contents. It occurs to me that timestamp information might be nice to have in pg_standby with debug mode. I might try patching pg_standby.c if no one beats me to it. -- Thomas F. O'Connell optimizing modern web applications : for search engines, for usability, and for performance : |
