On Thu, 2008-02-21 at 08:01 +0600, Markus Bertheau wrote: > (I sent this to -docs already, but it didn't get through for some reason.) > > >From the current 8.3 docs: > > Section 24.3.3.1 states about restore_command: > > "The command will be asked for file names that are not present in the > archive; it must return nonzero when so asked." > > Section 24.4.1 further states: > > "The magic that makes the two loosely coupled servers work together is > simply a restore_command used on the standby that waits for the next > WAL file to become available from the primary." > > It is not clear from the first paragraph, whether the non-existing > file that restore_command is being asked for is a not-yet-generated > WAL file or something different. If it was a not-yet-generated WAL > file, restore_command for replication would have to wait for it to > appear. If it was something different, restore_command for replication > would have to return an error right away. (Because else it would hang > indefinitely, waiting for a file that is not going to appear). Yet I > couldn't find hints in the documentation as to how these two cases can > be detected by restore_command, i.e. how restore_command should tell a > request for a WAL file from a request for a non-WAL file.
The two sentences aren't mutually exclusive, especially when you consider they are discussing two different use cases. Why not read up on pg_standby anyway? > Practice (http://archives.postgresql.org/sydpug/2006-10/msg00001.php) > shows that this is a problem, and people use unproved heuristics > ('history' substring in the requested file name). Old email written during beta. Read at your own peril. > Additionally, 24.3.3 contains slightly misleading information: > > "It is important that the command return nonzero exit status on > failure. The command will be asked for log files that are not present > in the archive; it must return nonzero when so asked. This is not an > error condition." > > This suggests that all non-existing files that restore_command will be > asked for are log files. One could therefore reasonably assume that > restore_command for replication should wait on all non-existing files. > 24.3.3.1 later corrects this by stating that not only log files may be > requested, but nevertheless. If you have some suggested changes, I'd be happy to hear them. Probably additions are better than just changes though. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
