Waiting for archive to complete

A number of people have complained that it is possible to make a base
backup and then shutdown the server before the last xlog file has been
archived. Others say they would like to be able to make a backup and
know it is complete.

Making the archiver continue while the file is archived can cause
problems when we do a restart, which has prevented some possible
solutions.

A simple solution is to introduce a new function:

pg_archive_wait(integer maxwait);
maxwait = 0 means wait forever, otherwise time measured in seconds.

This will get the current xlog position and wait for all files prior to
that point to be shown as archive done. Code to do this is very similar
to XLogArchiveCheckDone() in a wait loop, testing once per second.

Simple enough for this release?

Comments?

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com