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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="UPGRADING"
>17.6. Upgrading a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> Cluster</A
></H1
><P
> This section discusses how to upgrade your database data from one
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> release to a newer one.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> major versions are represented by the
first two digit groups of the version number, e.g., 8.4.
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> minor versions are represented by the
third group of version digits, e.g., 8.4.2 is the second minor
release of 8.4. Minor releases never change the internal storage
format and are always compatible with earlier and later minor
releases of the same major version number, e.g., 8.4.2 is compatible
with 8.4, 8.4.1 and 8.4.6. To update between compatible versions,
you simply replace the executables while the server is down and
restart the server. The data directory remains unchanged —
minor upgrades are that simple.
</P
><P
> For <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>major</I
></SPAN
> releases of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, the
internal data storage format is subject to change, thus complicating
upgrades. The traditional method for moving data to a new major version
is to dump and reload the database. Other methods are available,
as discussed below.
</P
><P
> New major versions also typically introduce some user-visible
incompatibilities, so application programming changes might be required.
All user-visible changes are listed in the release notes (<A
HREF="release.html"
>Appendix E</A
>); pay particular attention to the section
labeled "Migration". If you are upgrading across several major
versions, be sure to read the release notes for each intervening
version.
</P
><P
> Cautious users will want to test their client applications on the new
version before switching over fully; therefore, it's often a good idea to
set up concurrent installations of old and new versions. When
testing a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> major upgrade, consider the
following categories of possible changes:
</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>Administration</DT
><DD
><P
> The capabilities available for administrators to monitor and control
the server often change and improve in each major release.
</P
></DD
><DT
>SQL</DT
><DD
><P
> Typically this includes new SQL command capabilities and not changes
in behavior, unless specifically mentioned in the release notes.
</P
></DD
><DT
>Library API</DT
><DD
><P
> Typically libraries like <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> only add new
functionality, again unless mentioned in the release notes.
</P
></DD
><DT
>System Catalogs</DT
><DD
><P
> System catalog changes usually only affect database management tools.
</P
></DD
><DT
>Server C-language API</DT
><DD
><P
> This involves changes in the backend function API, which is written
in the C programming language. Such changes affect code that
references backend functions deep inside the server.
</P
></DD
></DL
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="UPGRADE-METHODS-PGDUMP"
>17.6.1. Upgrading Data via <SPAN
CLASS="APPLICATION"
>pg_dump</SPAN
></A
></H2
><P
> To dump data from one major version of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> and
reload it in another, you must use <SPAN
CLASS="APPLICATION"
>pg_dump</SPAN
>; file system
level backup methods will not work. (There are checks in place that prevent
you from using a data directory with an incompatible version of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, so no great harm can be done by
trying to start the wrong server version on a data directory.)
</P
><P
> It is recommended that you use the <SPAN
CLASS="APPLICATION"
>pg_dump</SPAN
> and
<SPAN
CLASS="APPLICATION"
>pg_dumpall</SPAN
> programs from the newer version of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, to take advantage of enhancements
that might have been made in these programs. Current releases of the
dump programs can read data from any server version back to 7.0.
</P
><P
> These instructions assume that your existing installation is under the
<TT
CLASS="FILENAME"
>/usr/local/pgsql</TT
> directory, and that the data area is in
<TT
CLASS="FILENAME"
>/usr/local/pgsql/data</TT
>. Substitute your paths
appropriately.
</P
><DIV
CLASS="PROCEDURE"
><OL
TYPE="1"
><LI
CLASS="STEP"
><P
> If making a backup, make sure that your database is not being updated.
This does not affect the integrity of the backup, but the changed
data would of course not be included. If necessary, edit the
permissions in the file <TT
CLASS="FILENAME"
>/usr/local/pgsql/data/pg_hba.conf</TT
>
(or equivalent) to disallow access from everyone except you.
See <A
HREF="client-authentication.html"
>Chapter 19</A
> for additional information on
access control.
</P
><P
>
To back up your database installation, type:
</P><PRE
CLASS="SCREEN"
><KBD
CLASS="USERINPUT"
>pg_dumpall > <TT
CLASS="REPLACEABLE"
><I
>outputfile</I
></TT
></KBD
></PRE
><P>
If you need to preserve OIDs (such as when using them as
foreign keys), then use the <TT
CLASS="OPTION"
>-o</TT
> option when running
<SPAN
CLASS="APPLICATION"
>pg_dumpall</SPAN
>.
</P
><P
> To make the backup, you can use the <SPAN
CLASS="APPLICATION"
>pg_dumpall</SPAN
>
command from the version you are currently running. For best
results, however, try to use the <SPAN
CLASS="APPLICATION"
>pg_dumpall</SPAN
>
command from <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.3.9,
since this version contains bug fixes and improvements over older
versions. While this advice might seem idiosyncratic since you
haven't installed the new version yet, it is advisable to follow
it if you plan to install the new version in parallel with the
old version. In that case you can complete the installation
normally and transfer the data later. This will also decrease
the downtime.
</P
></LI
><LI
CLASS="STEP"
><P
> Shut down the old server:
</P><PRE
CLASS="SCREEN"
><KBD
CLASS="USERINPUT"
>pg_ctl stop</KBD
></PRE
><P>
On systems that have <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> started at boot time,
there is probably a start-up file that will accomplish the same thing. For
example, on a <SPAN
CLASS="SYSTEMITEM"
>Red Hat Linux</SPAN
> system one
might find that this works:
</P><PRE
CLASS="SCREEN"
><KBD
CLASS="USERINPUT"
>/etc/rc.d/init.d/postgresql stop</KBD
></PRE
><P>
See <A
HREF="runtime.html"
>Chapter 17</A
> for details about starting and
stopping the server.
</P
></LI
><LI
CLASS="STEP"
><P
> If restoring from backup, rename or delete the old installation
directory. It is a good idea to rename the directory, rather than
delete it, in case you have trouble and need to revert to it. Keep
in mind the directory might consume significant disk space. To rename
the directory, use a command like this:
</P><PRE
CLASS="SCREEN"
><KBD
CLASS="USERINPUT"
>mv /usr/local/pgsql /usr/local/pgsql.old</KBD
></PRE
><P>
(Be sure to move the directory as a single unit so relative paths
remain unchanged.)
</P
></LI
><LI
CLASS="STEP"
><P
> Install the new version of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> as
outlined in
<A
HREF="install-procedure.html"
>Section 15.4</A
>.
</P
></LI
><LI
CLASS="STEP"
><P
> Create a new database cluster if needed. Remember that you must
execute these commands while logged in to the special database user
account (which you already have if you are upgrading).
</P><PRE
CLASS="PROGRAMLISTING"
><KBD
CLASS="USERINPUT"
>/usr/local/pgsql/bin/initdb -D /usr/local/pgsql/data</KBD
></PRE
><P>
</P
></LI
><LI
CLASS="STEP"
><P
> Restore your previous <TT
CLASS="FILENAME"
>pg_hba.conf</TT
> and any
<TT
CLASS="FILENAME"
>postgresql.conf</TT
> modifications.
</P
></LI
><LI
CLASS="STEP"
><P
> Start the database server, again using the special database user
account:
</P><PRE
CLASS="PROGRAMLISTING"
><KBD
CLASS="USERINPUT"
>/usr/local/pgsql/bin/postgres -D /usr/local/pgsql/data</KBD
></PRE
><P>
</P
></LI
><LI
CLASS="STEP"
><P
> Finally, restore your data from backup with:
</P><PRE
CLASS="SCREEN"
><KBD
CLASS="USERINPUT"
>/usr/local/pgsql/bin/psql -d postgres -f <TT
CLASS="REPLACEABLE"
><I
>outputfile</I
></TT
></KBD
></PRE
><P>
using the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>new</I
></SPAN
> <SPAN
CLASS="APPLICATION"
>psql</SPAN
>.
</P
></LI
></OL
></DIV
><P
> The least downtime can be achieved by installing the new server in
a different directory and running both the old and the new servers
in parallel, on different ports. Then you can use something like:
</P><PRE
CLASS="PROGRAMLISTING"
>pg_dumpall -p 5432 | psql -d postgres -p 5433</PRE
><P>
to transfer your data.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="UPGRADING-METHODS-OTHER"
>17.6.2. Non-Dump Upgrade Methods</A
></H2
><P
> The <A
HREF="pgupgrade.html"
>pg_upgrade</A
> module allows an
installation to be migrated in-place from one major
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> version to the next. Upgrades can be
performed in minutes.
</P
><P
> It is also possible to use certain replication methods, such as
<SPAN
CLASS="PRODUCTNAME"
>Slony</SPAN
>, to create a standby server with the updated version of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>. This is possible because Slony supports
replication between different major versions of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>. The standby can be on the same computer or
a different computer. Once it has synced up with the master server
(running the older version of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>), you can
switch masters and make the standby the master and shut down the older
database instance. Such a switch-over results in only several seconds
of downtime for an upgrade.
</P
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