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Don't use SGML empty tags

Browse Source 
For DocBook XML compatibility, don't use SGML empty tags (</>) anymore,
replace by the full tag name.  Add a warning option to catch future
occurrences.

Alexander Lakhin, Jürgen Purtz
This commit is contained in:
Peter Eisentraut
2017-10-08 21:44:17 -04:00
parent 6ecabead4b
commit c29c578908
337 changed files with 31636 additions and 31635 deletions
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232
doc/src/sgml/ref/pgupgrade.sgml
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@@ -35,38 +35,38 @@
<title>Description</title>
<para>
<application>pg_upgrade</> (formerly called <application>pg_migrator</>) allows data
stored in <productname>PostgreSQL</> data files to be upgraded to a later <productname>PostgreSQL</>
<application>pg_upgrade</application> (formerly called <application>pg_migrator</application>) allows data
stored in <productname>PostgreSQL</productname> data files to be upgraded to a later <productname>PostgreSQL</productname>
major version without the data dump/reload typically required for
major version upgrades, e.g. from 9.6.3 to the current major release
of <productname>PostgreSQL</>. It is not required for minor version upgrades, e.g. from
of <productname>PostgreSQL</productname>. It is not required for minor version upgrades, e.g. from
9.6.2 to 9.6.3.
</para>
<para>
Major PostgreSQL releases regularly add new features that often
change the layout of the system tables, but the internal data storage
format rarely changes. <application>pg_upgrade</> uses this fact
format rarely changes. <application>pg_upgrade</application> uses this fact
to perform rapid upgrades by creating new system tables and simply
reusing the old user data files. If a future major release ever
changes the data storage format in a way that makes the old data
format unreadable, <application>pg_upgrade</> will not be usable
format unreadable, <application>pg_upgrade</application> will not be usable
for such upgrades. (The community will attempt to avoid such
situations.)
</para>
<para>
<application>pg_upgrade</> does its best to
<application>pg_upgrade</application> does its best to
make sure the old and new clusters are binary-compatible, e.g. by
checking for compatible compile-time settings, including 32/64-bit
binaries. It is important that
any external modules are also binary compatible, though this cannot
be checked by <application>pg_upgrade</>.
be checked by <application>pg_upgrade</application>.
</para>
<para>
pg_upgrade supports upgrades from 8.4.X and later to the current
major release of <productname>PostgreSQL</>, including snapshot and beta releases.
major release of <productname>PostgreSQL</productname>, including snapshot and beta releases.
</para>
</refsect1>
@@ -79,17 +79,17 @@
<variablelist>
<varlistentry>
<term><option>-b</option> <replaceable>bindir</></term>
<term><option>--old-bindir=</option><replaceable>bindir</></term>
<term><option>-b</option> <replaceable>bindir</replaceable></term>
<term><option>--old-bindir=</option><replaceable>bindir</replaceable></term>
<listitem><para>the old PostgreSQL executable directory;
environment variable <envar>PGBINOLD</></para></listitem>
environment variable <envar>PGBINOLD</envar></para></listitem>
</varlistentry>
<varlistentry>
<term><option>-B</option> <replaceable>bindir</></term>
<term><option>--new-bindir=</option><replaceable>bindir</></term>
<term><option>-B</option> <replaceable>bindir</replaceable></term>
<term><option>--new-bindir=</option><replaceable>bindir</replaceable></term>
<listitem><para>the new PostgreSQL executable directory;
environment variable <envar>PGBINNEW</></para></listitem>
environment variable <envar>PGBINNEW</envar></para></listitem>
</varlistentry>
<varlistentry>
@@ -99,17 +99,17 @@
</varlistentry>
<varlistentry>
<term><option>-d</option> <replaceable>datadir</></term>
<term><option>--old-datadir=</option><replaceable>datadir</></term>
<term><option>-d</option> <replaceable>datadir</replaceable></term>
<term><option>--old-datadir=</option><replaceable>datadir</replaceable></term>
<listitem><para>the old cluster data directory; environment
variable <envar>PGDATAOLD</></para></listitem>
variable <envar>PGDATAOLD</envar></para></listitem>
</varlistentry>
<varlistentry>
<term><option>-D</option> <replaceable>datadir</></term>
<term><option>--new-datadir=</option><replaceable>datadir</></term>
<term><option>-D</option> <replaceable>datadir</replaceable></term>
<term><option>--new-datadir=</option><replaceable>datadir</replaceable></term>
<listitem><para>the new cluster data directory; environment
variable <envar>PGDATANEW</></para></listitem>
variable <envar>PGDATANEW</envar></para></listitem>
</varlistentry>
<varlistentry>
@@ -143,17 +143,17 @@
</varlistentry>
<varlistentry>
<term><option>-p</option> <replaceable>port</></term>
<term><option>--old-port=</option><replaceable>port</></term>
<term><option>-p</option> <replaceable>port</replaceable></term>
<term><option>--old-port=</option><replaceable>port</replaceable></term>
<listitem><para>the old cluster port number; environment
variable <envar>PGPORTOLD</></para></listitem>
variable <envar>PGPORTOLD</envar></para></listitem>
</varlistentry>
<varlistentry>
<term><option>-P</option> <replaceable>port</></term>
<term><option>--new-port=</option><replaceable>port</></term>
<term><option>-P</option> <replaceable>port</replaceable></term>
<term><option>--new-port=</option><replaceable>port</replaceable></term>
<listitem><para>the new cluster port number; environment
variable <envar>PGPORTNEW</></para></listitem>
variable <envar>PGPORTNEW</envar></para></listitem>
</varlistentry>
<varlistentry>
@@ -164,10 +164,10 @@
</varlistentry>
<varlistentry>
<term><option>-U</option> <replaceable>username</></term>
<term><option>--username=</option><replaceable>username</></term>
<term><option>-U</option> <replaceable>username</replaceable></term>
<term><option>--username=</option><replaceable>username</replaceable></term>
<listitem><para>cluster's install user name; environment
variable <envar>PGUSER</></para></listitem>
variable <envar>PGUSER</envar></para></listitem>
</varlistentry>
<varlistentry>
@@ -207,17 +207,17 @@
<para>
If you are using a version-specific installation directory, e.g.
<filename>/opt/PostgreSQL/&majorversion;</>, you do not need to move the old cluster. The
<filename>/opt/PostgreSQL/&majorversion;</filename>, you do not need to move the old cluster. The
graphical installers all use version-specific installation directories.
</para>
<para>
If your installation directory is not version-specific, e.g.
<filename>/usr/local/pgsql</>, it is necessary to move the current PostgreSQL install
directory so it does not interfere with the new <productname>PostgreSQL</> installation.
Once the current <productname>PostgreSQL</> server is shut down, it is safe to rename the
<filename>/usr/local/pgsql</filename>, it is necessary to move the current PostgreSQL install
directory so it does not interfere with the new <productname>PostgreSQL</productname> installation.
Once the current <productname>PostgreSQL</productname> server is shut down, it is safe to rename the
PostgreSQL installation directory; assuming the old directory is
<filename>/usr/local/pgsql</>, you can do:
<filename>/usr/local/pgsql</filename>, you can do:
<programlisting>
mv /usr/local/pgsql /usr/local/pgsql.old
@@ -230,8 +230,8 @@ mv /usr/local/pgsql /usr/local/pgsql.old
<title>For source installs, build the new version</title>
<para>
Build the new PostgreSQL source with <command>configure</> flags that are compatible
with the old cluster. <application>pg_upgrade</> will check <command>pg_controldata</> to make
Build the new PostgreSQL source with <command>configure</command> flags that are compatible
with the old cluster. <application>pg_upgrade</application> will check <command>pg_controldata</command> to make
sure all settings are compatible before starting the upgrade.
</para>
</step>
@@ -241,7 +241,7 @@ mv /usr/local/pgsql /usr/local/pgsql.old
<para>
Install the new server's binaries and support
files. <application>pg_upgrade</> is included in a default installation.
files. <application>pg_upgrade</application> is included in a default installation.
</para>
<para>
@@ -273,7 +273,7 @@ make prefix=/usr/local/pgsql.new install
into the new cluster, e.g. <filename>pgcrypto.so</filename>,
whether they are from <filename>contrib</filename>
or some other source. Do not install the schema definitions, e.g.
<command>CREATE EXTENSION pgcrypto</>, because these will be upgraded
<command>CREATE EXTENSION pgcrypto</command>, because these will be upgraded
from the old cluster.
Also, any custom full text search files (dictionary, synonym,
thesaurus, stop words) must also be copied to the new cluster.
@@ -284,9 +284,9 @@ make prefix=/usr/local/pgsql.new install
<title>Adjust authentication</title>
<para>
<command>pg_upgrade</> will connect to the old and new servers several
times, so you might want to set authentication to <literal>peer</>
in <filename>pg_hba.conf</> or use a <filename>~/.pgpass</> file
<command>pg_upgrade</command> will connect to the old and new servers several
times, so you might want to set authentication to <literal>peer</literal>
in <filename>pg_hba.conf</filename> or use a <filename>~/.pgpass</filename> file
(see <xref linkend="libpq-pgpass">).
</para>
</step>
@@ -322,23 +322,23 @@ NET STOP postgresql-&majorversion;
<para>
If you are upgrading standby servers using methods outlined in section <xref
linkend="pgupgrade-step-replicas">, verify that the old standby
servers are caught up by running <application>pg_controldata</>
servers are caught up by running <application>pg_controldata</application>
against the old primary and standby clusters. Verify that the
<quote>Latest checkpoint location</> values match in all clusters.
<quote>Latest checkpoint location</quote> values match in all clusters.
(There will be a mismatch if old standby servers were shut down
before the old primary.) Also, change <varname>wal_level</> to
<literal>replica</> in the <filename>postgresql.conf</> file on the
before the old primary.) Also, change <varname>wal_level</varname> to
<literal>replica</literal> in the <filename>postgresql.conf</filename> file on the
new primary cluster.
</para>
</step>
<step>
<title>Run <application>pg_upgrade</></title>
<title>Run <application>pg_upgrade</application></title>
<para>
Always run the <application>pg_upgrade</> binary of the new server, not the old one.
<application>pg_upgrade</> requires the specification of the old and new cluster's
data and executable (<filename>bin</>) directories. You can also specify
Always run the <application>pg_upgrade</application> binary of the new server, not the old one.
<application>pg_upgrade</application> requires the specification of the old and new cluster's
data and executable (<filename>bin</filename>) directories. You can also specify
user and port values, and whether you want the data files linked
instead of the default copy behavior.
</para>
@@ -349,13 +349,13 @@ NET STOP postgresql-&majorversion;
your old cluster
once you start the new cluster after the upgrade. Link mode also
requires that the old and new cluster data directories be in the
same file system. (Tablespaces and <filename>pg_wal</> can be on
different file systems.) See <literal>pg_upgrade --help</> for a full
same file system. (Tablespaces and <filename>pg_wal</filename> can be on
different file systems.) See <literal>pg_upgrade --help</literal> for a full
list of options.
</para>
<para>
The <option>--jobs</> option allows multiple CPU cores to be used
The <option>--jobs</option> option allows multiple CPU cores to be used
for copying/linking of files and to dump and reload database schemas
in parallel; a good place to start is the maximum of the number of
CPU cores and tablespaces. This option can dramatically reduce the
@@ -365,14 +365,14 @@ NET STOP postgresql-&majorversion;
<para>
For Windows users, you must be logged into an administrative account, and
then start a shell as the <literal>postgres</> user and set the proper path:
then start a shell as the <literal>postgres</literal> user and set the proper path:
<programlisting>
RUNAS /USER:postgres "CMD.EXE"
SET PATH=%PATH%;C:\Program Files\PostgreSQL\&majorversion;\bin;
</programlisting>
and then run <application>pg_upgrade</> with quoted directories, e.g.:
and then run <application>pg_upgrade</application> with quoted directories, e.g.:
<programlisting>
pg_upgrade.exe
@@ -382,19 +382,19 @@ pg_upgrade.exe
--new-bindir "C:/Program Files/PostgreSQL/&majorversion;/bin"
</programlisting>
Once started, <command>pg_upgrade</> will verify the two clusters are compatible
and then do the upgrade. You can use <command>pg_upgrade --check</>
Once started, <command>pg_upgrade</command> will verify the two clusters are compatible
and then do the upgrade. You can use <command>pg_upgrade --check</command>
to perform only the checks, even if the old server is still
running. <command>pg_upgrade --check</> will also outline any
running. <command>pg_upgrade --check</command> will also outline any
manual adjustments you will need to make after the upgrade. If you
are going to be using link mode, you should use the <option>--link</>
are going to be using link mode, you should use the <option>--link</option>
option with <option>--check</option> to enable link-mode-specific checks.
<command>pg_upgrade</> requires write permission in the current directory.
<command>pg_upgrade</command> requires write permission in the current directory.
</para>
<para>
Obviously, no one should be accessing the clusters during the
upgrade. <application>pg_upgrade</> defaults to running servers
upgrade. <application>pg_upgrade</application> defaults to running servers
on port 50432 to avoid unintended client connections.
You can use the same port number for both clusters when doing an
upgrade because the old and new clusters will not be running at the
@@ -403,7 +403,7 @@ pg_upgrade.exe
</para>
<para>
If an error occurs while restoring the database schema, <command>pg_upgrade</> will
If an error occurs while restoring the database schema, <command>pg_upgrade</command> will
exit and you will have to revert to the old cluster as outlined in <xref linkend="pgupgrade-step-revert">
below. To try <command>pg_upgrade</command> again, you will need to modify the old
cluster so the pg_upgrade schema restore succeeds. If the problem is a
@@ -420,16 +420,16 @@ pg_upgrade.exe
If you used link mode and have Streaming Replication (see <xref
linkend="streaming-replication">) or Log-Shipping (see <xref
linkend="warm-standby">) standby servers, you can follow these steps to
quickly upgrade them. You will not be running <application>pg_upgrade</> on
the standby servers, but rather <application>rsync</> on the primary.
quickly upgrade them. You will not be running <application>pg_upgrade</application> on
the standby servers, but rather <application>rsync</application> on the primary.
Do not start any servers yet.
</para>
<para>
If you did <emphasis>not</> use link mode, do not have or do not
want to use <application>rsync</>, or want an easier solution, skip
If you did <emphasis>not</emphasis> use link mode, do not have or do not
want to use <application>rsync</application>, or want an easier solution, skip
the instructions in this section and simply recreate the standby
servers once <application>pg_upgrade</> completes and the new primary
servers once <application>pg_upgrade</application> completes and the new primary
is running.
</para>
@@ -445,11 +445,11 @@ pg_upgrade.exe
</step>
<step>
<title>Make sure the new standby data directories do <emphasis>not</> exist</title>
<title>Make sure the new standby data directories do <emphasis>not</emphasis> exist</title>
<para>
Make sure the new standby data directories do <emphasis>not</>
exist or are empty. If <application>initdb</> was run, delete
Make sure the new standby data directories do <emphasis>not</emphasis>
exist or are empty. If <application>initdb</application> was run, delete
the standby servers' new data directories.
</para>
</step>
@@ -477,32 +477,32 @@ pg_upgrade.exe
<para>
Save any configuration files from the old standbys' data
directories you need to keep, e.g. <filename>postgresql.conf</>,
<literal>recovery.conf</>, because these will be overwritten or
directories you need to keep, e.g. <filename>postgresql.conf</filename>,
<literal>recovery.conf</literal>, because these will be overwritten or
removed in the next step.
</para>
</step>
<step>
<title>Run <application>rsync</></title>
<title>Run <application>rsync</application></title>
<para>
When using link mode, standby servers can be quickly upgraded using
<application>rsync</>. To accomplish this, from a directory on
<application>rsync</application>. To accomplish this, from a directory on
the primary server that is above the old and new database cluster
directories, run this on the <emphasis>primary</> for each standby
directories, run this on the <emphasis>primary</emphasis> for each standby
server:
<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive old_pgdata new_pgdata remote_dir
</programlisting>
where <option>old_pgdata</> and <option>new_pgdata</> are relative
to the current directory on the primary, and <option>remote_dir</>
is <emphasis>above</> the old and new cluster directories
where <option>old_pgdata</option> and <option>new_pgdata</option> are relative
to the current directory on the primary, and <option>remote_dir</option>
is <emphasis>above</emphasis> the old and new cluster directories
on the standby. The directory structure under the specified
directories on the primary and standbys must match. Consult the
<application>rsync</> manual page for details on specifying the
<application>rsync</application> manual page for details on specifying the
remote directory, e.g.
<programlisting>
@@ -511,37 +511,37 @@ rsync --archive --delete --hard-links --size-only --no-inc-recursive /opt/Postgr
</programlisting>
You can verify what the command will do using
<application>rsync</>'s <option>--dry-run</> option. While
<application>rsync</> must be run on the primary for at least one
standby, it is possible to run <application>rsync</> on an upgraded
<application>rsync</application>'s <option>--dry-run</option> option. While
<application>rsync</application> must be run on the primary for at least one
standby, it is possible to run <application>rsync</application> on an upgraded
standby to upgrade other standbys, as long as the upgraded standby
has not been started.
</para>
<para>
What this does is to record the links created by
<application>pg_upgrade</>'s link mode that connect files in the
<application>pg_upgrade</application>'s link mode that connect files in the
old and new clusters on the primary server. It then finds matching
files in the standby's old cluster and creates links for them in the
standby's new cluster. Files that were not linked on the primary
are copied from the primary to the standby. (They are usually
small.) This provides rapid standby upgrades. Unfortunately,
<application>rsync</> needlessly copies files associated with
<application>rsync</application> needlessly copies files associated with
temporary and unlogged tables because these files don't normally
exist on standby servers.
</para>
<para>
If you have tablespaces, you will need to run a similar
<application>rsync</> command for each tablespace directory, e.g.:
<application>rsync</application> command for each tablespace directory, e.g.:
<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tblsp/PG_9.5_201510051 \
/vol1/pg_tblsp/PG_9.6_201608131 standby.example.com:/vol1/pg_tblsp
</programlisting>
If you have relocated <filename>pg_wal</> outside the data
directories, <application>rsync</> must be run on those directories
If you have relocated <filename>pg_wal</filename> outside the data
directories, <application>rsync</application> must be run on those directories
too.
</para>
</step>
@@ -551,7 +551,7 @@ rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tb
<para>
Configure the servers for log shipping. (You do not need to run
<function>pg_start_backup()</> and <function>pg_stop_backup()</>
<function>pg_start_backup()</function> and <function>pg_stop_backup()</function>
or take a file system backup as the standbys are still synchronized
with the primary.)
</para>
@@ -562,12 +562,12 @@ rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tb
</step>
<step>
<title>Restore <filename>pg_hba.conf</></title>
<title>Restore <filename>pg_hba.conf</filename></title>
<para>
If you modified <filename>pg_hba.conf</>, restore its original settings.
If you modified <filename>pg_hba.conf</filename>, restore its original settings.
It might also be necessary to adjust other configuration files in the new
cluster to match the old cluster, e.g. <filename>postgresql.conf</>.
cluster to match the old cluster, e.g. <filename>postgresql.conf</filename>.
</para>
</step>
@@ -576,7 +576,7 @@ rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tb
<para>
The new server can now be safely started, and then any
<application>rsync</>'ed standby servers.
<application>rsync</application>'ed standby servers.
</para>
</step>
@@ -612,7 +612,7 @@ psql --username=postgres --file=script.sql postgres
<title>Statistics</title>
<para>
Because optimizer statistics are not transferred by <command>pg_upgrade</>, you will
Because optimizer statistics are not transferred by <command>pg_upgrade</command>, you will
be instructed to run a command to regenerate that information at the end
of the upgrade. You might need to set connection parameters to
match your new cluster.
@@ -628,7 +628,7 @@ psql --username=postgres --file=script.sql postgres
<command>pg_upgrade</command> completes. (Automatic deletion is not
possible if you have user-defined tablespaces inside the old data
directory.) You can also delete the old installation directories
(e.g. <filename>bin</>, <filename>share</>).
(e.g. <filename>bin</filename>, <filename>share</filename>).
</para>
</step>
@@ -643,7 +643,7 @@ psql --username=postgres --file=script.sql postgres
<listitem>
<para>
If you ran <command>pg_upgrade</command>
with <option>--check</>, no modifications were made to the old
with <option>--check</option>, no modifications were made to the old
cluster and you can re-use it anytime.
</para>
</listitem>
@@ -651,7 +651,7 @@ psql --username=postgres --file=script.sql postgres
<listitem>
<para>
If you ran <command>pg_upgrade</command>
with <option>--link</>, the data files are shared between the
with <option>--link</option>, the data files are shared between the
old and new cluster. If you started the new cluster, the new
server has written to those shared files and it is unsafe to
use the old cluster.
@@ -660,13 +660,13 @@ psql --username=postgres --file=script.sql postgres
<listitem>
<para>
If you ran <command>pg_upgrade</command> <emphasis>without</>
<option>--link</> or did not start the new server, the
If you ran <command>pg_upgrade</command> <emphasis>without</emphasis>
<option>--link</option> or did not start the new server, the
old cluster was not modified except that, if linking
started, a <literal>.old</> suffix was appended to
<filename>$PGDATA/global/pg_control</>. To reuse the old
cluster, possibly remove the <filename>.old</> suffix from
<filename>$PGDATA/global/pg_control</>; you can then restart the
started, a <literal>.old</literal> suffix was appended to
<filename>$PGDATA/global/pg_control</filename>. To reuse the old
cluster, possibly remove the <filename>.old</filename> suffix from
<filename>$PGDATA/global/pg_control</filename>; you can then restart the
old cluster.
</para>
</listitem>
@@ -681,16 +681,16 @@ psql --username=postgres --file=script.sql postgres
<title>Notes</title>
<para>
<application>pg_upgrade</> does not support upgrading of databases
containing these <type>reg*</> OID-referencing system data types:
<type>regproc</>, <type>regprocedure</>, <type>regoper</>,
<type>regoperator</>, <type>regconfig</>, and
<type>regdictionary</>. (<type>regtype</> can be upgraded.)
<application>pg_upgrade</application> does not support upgrading of databases
containing these <type>reg*</type> OID-referencing system data types:
<type>regproc</type>, <type>regprocedure</type>, <type>regoper</type>,
<type>regoperator</type>, <type>regconfig</type>, and
<type>regdictionary</type>. (<type>regtype</type> can be upgraded.)
</para>
<para>
All failure, rebuild, and reindex cases will be reported by
<application>pg_upgrade</> if they affect your installation;
<application>pg_upgrade</application> if they affect your installation;
post-upgrade scripts to rebuild tables and indexes will be
generated automatically. If you are trying to automate the upgrade
of many clusters, you should find that clusters with identical database
@@ -705,17 +705,17 @@ psql --username=postgres --file=script.sql postgres
</para>
<para>
If you are upgrading a pre-<productname>PostgreSQL</> 9.2 cluster
If you are upgrading a pre-<productname>PostgreSQL</productname> 9.2 cluster
that uses a configuration-file-only directory, you must pass the
real data directory location to <application>pg_upgrade</>, and
real data directory location to <application>pg_upgrade</application>, and
pass the configuration directory location to the server, e.g.
<literal>-d /real-data-directory -o '-D /configuration-directory'</>.
<literal>-d /real-data-directory -o '-D /configuration-directory'</literal>.
</para>
<para>
If using a pre-9.1 old server that is using a non-default Unix-domain
socket directory or a default that differs from the default of the
new cluster, set <envar>PGHOST</> to point to the old server's socket
new cluster, set <envar>PGHOST</envar> to point to the old server's socket
location. (This is not relevant on Windows.)
</para>
@@ -723,13 +723,13 @@ psql --username=postgres --file=script.sql postgres
If you want to use link mode and you do not want your old cluster
to be modified when the new cluster is started, make a copy of the
old cluster and upgrade that in link mode. To make a valid copy
of the old cluster, use <command>rsync</> to create a dirty
of the old cluster, use <command>rsync</command> to create a dirty
copy of the old cluster while the server is running, then shut down
the old server and run <command>rsync --checksum</> again to update the
copy with any changes to make it consistent. (<option>--checksum</>
is necessary because <command>rsync</> only has file modification-time
the old server and run <command>rsync --checksum</command> again to update the
copy with any changes to make it consistent. (<option>--checksum</option>
is necessary because <command>rsync</command> only has file modification-time
granularity of one second.) You might want to exclude some
files, e.g. <filename>postmaster.pid</>, as documented in <xref
files, e.g. <filename>postmaster.pid</filename>, as documented in <xref
linkend="backup-lowlevel-base-backup">. If your file system supports
file system snapshots or copy-on-write file copies, you can use that
to make a backup of the old cluster and tablespaces, though the snapshot