Re: Something else about Redo Logs disappearing

[Peter]

Actually, the affair had some good side: as usual I was checking                
my own designs first and looking for flaws, and indeed I found one:             
                                                                                
If you do copy out the archive logs not directly to tape, but to                
some disk area for further processing, then there is an issue with              
possible loss. If you do it like the docs say, with a command like              
this:                                                                           
                                                                                
archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p                 
+/mnt/server/archivedir/%f'  # Unix                                             
                                                                                
That "cp" is usually not synchronous. So there is the possibility               
that this command terminates successfully, and reports exitcode zero            
back to the Postgres, and then the Postgres will consider that log              
being safely away.                                                              
                                                                                
But the target of the copy may not yet been written to disk. If                 
at that point a power loss happens, the log may become missing/damaged/         
incomplete, while the database may or may not consider it done                  
when restarting.                                                                
                                                                                
Therefore, mounting such a target filesystem in all-synchronous mode            
might be a good idea. (UFS: "-o sync", ZFS: "set sync=always")                  
                                                                                
cheerio,                                                                        
PMc