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Edited for grammar, idiom, and style. Notice that "backup" is a noun,

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and "back up" is a verb. Adjusted capitalization in titles.
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server/databases/upgradedb.xml
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@ -12,7 +12,7 @@
<date>$Date$</date>
</sect1info>
<title>Important notes about upgrading Database Server Software</title>
<title>Important Notes About Upgrading Database Server Software</title>
<note><para>This section is about reinstalling database software
when an existing database is in use. It is not applicable for
@ -20,9 +20,9 @@
the package being updated, but users should read through it
to become aware of issues that can arise in the future.</para></note>
<para>Lets start this chapter with a dramatic screenshot of an issue that
really happened. This issue will not occur if you are going to install the
software the first time:</para>
<para>Let's start this chapter with a dramatic screenshot of an error that
really happened. This error will not occur if you are installing database
software for the first time:</para>
<screen>$ sudo systemctl status postgresql
-- postgresql.service - PostgreSQL database server
@ -44,85 +44,83 @@ Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Failed with result 'exit
Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.</screen>
<para>
To avoid situations like the one above finding your database server
software refusing to start, read the following thoughts about how to
upgrade a DBMS (Database Management System) prior to actually doing the
upgrade.
To avoid situations like this (i.e., your database server
software refuses to start), read the following discussion of the best way to
upgrade a DBMS (Database Management System).
</para>
<para>
The root cause of the issue shown above was an upgrade
of the server software to a newer major version but leaving the
data files untouched. The administrator was able to recover without any
loss of data.
The root cause of the error shown above was an upgrade
of the server software to a newer major version which left the
data files untouched. In this case, the administrator was able to recover
the DBMS without any loss of data.
</para>
<para>
Even if you are doing an install DBMS install, read through this
section. Tt will provide you information about how to set up backup
and restore procedures (at least the strategy for building
them) which are sufficient for your needs and for the safety
Even if you are doing an initiall DBMS install, read through this
section. It provides information about implementing backup
and restore procedures (or at least a strategy for creating
them) which will satisfy your needs and guarantee the safety
of your data.
</para>
<sect2>
<title>Upgrade database server packages</title>
<title>Upgrade Database Server Packages</title>
<para>
Database systems work on files which hold the database metadata and the
data itself. Those files are highly optimized in their internal
structures for use by the server software. When upgrading such server
software, newer server software may expect a different file format than
was created by previous versions. In the best case, the new software can
act on the old format as well&mdash;but not benefitting from newer
formats which might result in better performance or of other
improvements. It can also happen that the new server software will
reformat the data files automatically when starting.
data itself. The internal structure of these files is optimized for use
by the server software. When such server software is upgraded,
the new software may utilize a different file format than
had previously been used. Sometimes the new software can
work with the old format as well as the new one&mdash;but wiithout the
performance improvements the new format provides.
Other times, the new server software will
reformat the data files automatically after the upgrade.
</para>
<para>
Unfortunately, the most likely case is that the new server software
complains about out of date file formats and exits. When this happens
and you have overwritten the installed server software, you may not be
able to read the data files and the new software is unwilling to do so.
complains about out of date file formats and exits. When this happens,
and you have overwritten the old server software, you may end up
with a broken system and lost data.
</para>
<para>
Changes in data file formats usually happen at major version changes but
potentially can come at other times. Before upgrading the server
software, check the documentation if there are changes which will
Changes in data file formats usually happen at major version changes, but
they can also occur at other times. Before upgrading any DBMS
software, check the documentation to see if this upgrade makes changes which
require reformatting the database.
</para>
<para>
Of course, if you have databases with content which is not easy to
rebuild, it is always a good idea to create backups of the database from
time to time. When upgrading the server software, it is time to run
Of course, if you have databases with content that is not easily
rebuilt, it is always a good idea to create backups of the database from
time to time. Before upgrading the server software, you should run
another backup.
</para>
<sect3>
<title>Upgrade by backup and restore</title>
<title>Upgrade by Backup and Restore</title>
<note>
<para>
A backup is meaningless if there is no verified process
A backup is useless if there is no verified process
to restore the data from this backup. When running a
database server, you should not only create backups but you
should also verify that the process you designed to fulfill
the restore task is working properly. When you encounter a
problem with the restore when you urgently have to
rely on the backup data, it is too late&mdash;your database is
in danger.
database server, you should not only create backups; you
should also verify that the restore process
really works. The time to test the restore procedure
is <emphasis>before</emphasis> you urgently need
to recover lost data.
</para>
</note>
<para>
In general, most (all?) database server software provides some basic
Most database server software provides some basic
tools to create backups of your data. Usually the backups created with
those tools can be read by newer versions of the software (via a
restore tool). Using older restore tools with newer backup data is not
defined and you should <emphasis>never</emphasis> blindly assume that
restore tool). Using older restore tools with newer backup data is
a bad idea; you should <emphasis>never</emphasis> blindly assume that
it will work. It might, but usually it doesn't.
</para>
@ -134,31 +132,28 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
<listitem>
<para>Create a full database backup using the old tools.</para>
<para>This step creates an offline copy of the database files ready
to be used for long term archiving, for disaster recovery, or just
preparation for upgrade. This offline backup consists of the full
one-to-one copy of the current database files or a backup of the
files from a certain time in history plus all journal data (that is
<para>This step creates an offline copy of the database files&mdash;for
long term archiving, for disaster recovery, or as
preparation for an upgrade. This offline backup consists of either (1) a full
one-to-one copy of the current database files, or (2) a full backup of the
database files from a certain point in time, plus all the journal data (that is
Oracle&reg; terminology, it is called "Continuous Archiving" or
"write ahead log (WAL)" in Postgresql) containing information about
changes made to the data content. The later take less time to create
if the DB software provides this type of journaling as you only have
to save the changes after creating the last backup. The amount of
data to backup is much less than doing a full backup every
time.</para>
"write ahead log (WAL)" in Postgresql) describing the
changes made after that point in time. This second form takes less time to create
(if the DB software provides this type of journaling) because you only have
to save the data that have changed since the last full backup was created.</para>
<para>In terms of upgrading database server software, a full backup
<para>When upgrading database server software, a full backup
(which can be used for subsequent incremental backups) should be
made, but if the amount of data is too big, an incremental backup will
be sufficient. Which strategy is appropriate for you depends on
created; but if there is a lot of data, an incremental backup will
suffice. The best strategy for you depends on
the amount of data stored in your database (is it a few hundred table
rows or is it hundreds of terabytes?). A full backup of the later one
isn't done quickly (and we assume that the underlying system of such
a database is probably not on an LFS system). To close the last gap
to fully protect your data, create a backup of the corresponding old
binaries (and/or their sources) and store it along with the data
files to make sure that there is a fallback solution if
the newer software is not able to read the older data.</para>
rows, or is it hundreds of terabytes?). A full backup in the latter case
can't be done quickly. To
fully protect your data, create a backup of the old
programs (and/or their sources) and save it, along with the data
files, to be certain there is a fallback solution if
the new software cannot read the old data.</para>
</listitem>
<listitem>
@ -176,15 +171,15 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
<para>To restore the data, the tools of the newly installed server
software should be used. During the restoration process, the new
tools will create and/or upgrade the data files in the format the
software requires. It is assumed that newer software is capable of
new software requires. It is assumed that newer software is capable of
reading old data.</para>
</listitem>
</itemizedlist>
<para>
Since you have already have a backup procedure in place (and you
Since you already have a backup procedure in place (and you
have tested your restore procedure, right?), this might
be the easiest way to upgrade as you are going to use your well known
be the easiest way to upgrade as you can use your well known
processes to upgrade just as you always do&mdash;at least in terms
of the backup and restore.
</para>
@ -192,27 +187,21 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
</sect3>
<sect3>
<title>Upgrade the database files by using system tools</title>
<title>Upgrade the Database Files by Using System Tools</title>
<para>
Some database systems (for instance Postgresql) provide
a tool which can reformat (upgrade) the existing database
files to the new format. Since the upgrading tool has to
be used from the new server software (the old one cannot
know anything about a new file format), the old software
might be overwritten due to installation of the new software.
files to the new format.
If you need to restore from a backup (for example, running
the upgrade tool failed) you will have to reinstall the old software
to recover your data.
</para>
<para>
In case you have to restore a backup (for example, running
the upgrade tool failed) you have to reinstall the old version
to get back the access to your data.
</para>
<para>
Even though those tools might work with one of the actual database
files, you should create a full backup before running them. A failure
might result in a serious damage of the database files.
Even though the reformatting tools might work as advertised,
you should create a full backup before running them. A failure
could cause serious damage to the database.
</para>
</sect3>
@ -220,7 +209,7 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
</sect2>
<sect2>
<title>Notes for specific DBMS</title>
<title>Notes for Specific DBMS</title>
<sect3>
<title>PostgreSQL</title>
@ -250,9 +239,9 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
<!-- might add some advanced notes for the DBMS here -->
<para>Do not underestimate <application>Sqlite</application>. It is a
feature rich DBMS. The main difference from the two big players above is
feature-rich DBMS. The main difference from the two big players above is
that Sqlite does not provide access via a network API. Sqlite databases
are files always stored on the same machine as the running program which
are always stored on the machine running the program which
uses the database. The manipulation of data content is done via API calls
to library functions directly within the program.</para>
@ -268,9 +257,9 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
</para>
<para>Unfortunately, there is no dedicated chapter in the
upstream documentation talking about backup/restore but
upstream documentation talking about backup/restore, but
there are several articles about it on the
Internet. One example is shown below.</para>
Internet. Here is an example.</para>
<para>Documentation for Backup/Restore:
<ulink url="https://database.guide/backup-sqlite-database/"/>
@ -283,11 +272,11 @@ Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.<
<!-- might add some advanced notes for the DBMS here -->
<para>Just like <application>Sqlite</application> this
software acts on local database files meaning there is no
<para>Like <application>Sqlite</application>, this
software acts on local database files; there is no
network interface.</para>
<para>The relevant resources for Backup/Restore a Berkeley database
<para>The relevant resources to back up/restore a Berkeley database
are the man pages for <filename>db_dump</filename> and its
counterpart <filename>db_load</filename>.</para>