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pg_upgrade: document use of rsync for slave upgrades
Also document that rsync has one-second granularity for file change comparisons. Report by Stephen Frost
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‎doc/src/sgml/backup.sgml‎

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@@ -438,8 +438,10 @@ tar -cf backup.tar /usr/local/pgsql/data
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Another option is to use <application>rsync</> to perform a file
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system backup. This is done by first running <application>rsync</>
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while the database server is running, then shutting down the database
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server just long enough to do a second <application>rsync</>. The
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second <application>rsync</> will be much quicker than the first,
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server long enough to do an <command>rsync --checksum</>.
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(<option>--checksum</> is necessary because <command>rsync</> only
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has file modification-time granularity of one second.) The
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second <application>rsync</> will be quicker than the first,
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because it has relatively little data to transfer, and the end result
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will be consistent because the server was down. This method
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allows a file system backup to be performed with minimal downtime.

‎doc/src/sgml/pgupgrade.sgml‎

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@@ -315,6 +315,11 @@ NET STOP postgresql-8.4
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NET STOP postgresql-9.0
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</programlisting>
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</para>
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<para>
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Streaming replication and log-shipping standby servers can remain running until
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a later step.
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</para>
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</step>
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<step>
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</para>
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</step>
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<step>
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<title>Upgrade Streaming Replication and Log-Shipping standby
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servers</title>
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<para>
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If you have Streaming Replication (<xref
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linkend="streaming-replication">) or Log-Shipping (<xref
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linkend="warm-standby">) standby servers, follow these steps to
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upgrade them (before starting any servers):
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</para>
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<procedure>
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<step>
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<title>Install the new PostgreSQL binaries on standby servers</title>
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<para>
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Make sure the new binaries and support files are installed on all
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standby servers.
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</para>
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</step>
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<step>
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<title>Make sure the new standby data directories do <emphasis>not</>
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exist</title>
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<para>
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Make sure the new standby data directories do <emphasis>not</>
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exist or are empty. If <application>initdb</> was run, delete
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the standby server data directories.
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</para>
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</step>
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<step>
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<title>Install custom shared object files</title>
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<para>
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Install the same custom shared object files on the new standbys
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that you installed in the new master cluster.
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</para>
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</step>
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<step>
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<title>Stop standby servers</title>
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<para>
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If the standby servers are still running, stop them now using the
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above instructions.
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</para>
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</step>
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<step>
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<title>Verify standby servers</title>
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<para>
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To prevent old standby servers from being modified, run
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<application>pg_controldata</> against the primary and standby
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clusters and verify that the <quote>Latest checkpoint location</>
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values match in all clusters. (This requires the standbys to be
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shut down after the primary.)
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</para>
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</step>
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<step>
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<title>Save configuration files</title>
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<para>
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Save any configuration files from the standbys you need to keep,
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e.g. <filename>postgresql.conf</>, <literal>recovery.conf</>,
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as these will be overwritten or removed in the next step.
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</para>
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</step>
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<step>
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<title>Start and stop the new master cluster</title>
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<para>
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In the new master cluster, change <varname>wal_level</> to
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<literal>hot_standby</> in the <filename>postgresql.conf</> file
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and then start and stop the cluster.
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</para>
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</step>
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<step>
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<title>Run <application>rsync</></title>
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<para>
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From a directory that is above the old and new database cluster
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directories, run this for each slave:
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<programlisting>
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rsync --archive --delete --hard-links --size-only old_pgdata new_pgdata remote_dir
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</programlisting>
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where <option>old_pgdata</> and <option>new_pgdata</> are relative
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to the current directory, and <option>remote_dir</> is
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<emphasis>above</> the old and new cluster directories on
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the standby server. The old and new relative cluster paths
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must match on the master and standby server. Consult the
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<application>rsync</> manual page for details on specifying the
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remote directory, e.g. <literal>standbyhost:/opt/PostgreSQL/</>.
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<application>rsync</> will be fast when <application>pg_upgrade</>'s
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<option>--link</> mode is used because it will create hard links
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on the remote server rather than transferring user data.
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</para>
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<para>
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If you have tablespaces, you will need to run a similar
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<application>rsync</> command for each tablespace directory. If you
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have relocated <filename>pg_xlog</> outside the data directories,
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<application>rsync</> must be run on those directories too.
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</para>
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</step>
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<step>
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<title>Configure streaming replication and log-shipping standby
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servers</title>
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<para>
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Configure the servers for log shipping. (You do not need to run
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<function>pg_start_backup()</> and <function>pg_stop_backup()</>
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or take a file system backup as the slaves are still synchronized
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with the master.)
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</para>
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</step>
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</procedure>
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</step>
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<step>
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<title>Restore <filename>pg_hba.conf</></title>
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</para>
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</step>
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<step>
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<title>Start the new server</title>
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<para>
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The new server can now be safely started, and then any
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<application>rsync</>'ed standby servers.
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</para>
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</step>
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<step>
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<title>Post-Upgrade processing</title>
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@@ -547,23 +691,16 @@ psql --username postgres --file script.sql postgres
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location. (This is not relevant on Windows.)
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</para>
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<para>
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A Log-Shipping Standby Server (<xref linkend="warm-standby">) cannot
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be upgraded because the server must allow writes. The simplest way
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is to upgrade the primary and use <command>rsync</> to rebuild the
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standbys. You can run <command>rsync</> while the primary is down,
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or as part of a base backup (<xref linkend="backup-base-backup">)
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which overwrites the old standby cluster.
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</para>
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<para>
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If you want to use link mode and you do not want your old cluster
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to be modified when the new cluster is started, make a copy of the
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old cluster and upgrade that in link mode. To make a valid copy
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of the old cluster, use <command>rsync</> to create a dirty
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copy of the old cluster while the server is running, then shut down
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the old server and run <command>rsync</> again to update the copy with any
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changes to make it consistent. You might want to exclude some
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the old server and run <command>rsync --checksum</> again to update the
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copy with any changes to make it consistent. (<option>--checksum</>
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is necessary because <command>rsync</> only has file modification-time
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granularity of one second.) You might want to exclude some
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files, e.g. <filename>postmaster.pid</>, as documented in <xref
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linkend="backup-lowlevel-base-backup">. If your file system supports
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file system snapshots or copy-on-write file copies, you can use that

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