[bcdfc53] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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| 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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| 4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <sect1 id="upgradedb" xreflabel="Upgrade Database">
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| 9 | <?dbhtml filename="upgradedb.html"?>
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| 10 |
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| 11 | <sect1info>
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| 12 | <date>$Date$</date>
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| 13 | </sect1info>
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| 14 |
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| 15 | <title>Notes on Database Server Software</title>
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| 16 |
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| 17 | <screen>$ sudo systemctl status postgresql
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| 18 | -- postgresql.service - PostgreSQL database server
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| 19 | Loaded: loaded (/usr/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
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| 20 | Active: failed (Result: exit-code) since Tue 2021-10-26 17:11:53 CDT; 2min 49s ago
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| 21 | Process: 17336 ExecStart=/usr/bin/pg_ctl -s -D ${PGROOT}/data start -w -t 120 (code=exited, status=1/FAILURE)
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| 22 | CPU: 7ms
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| 23 |
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| 24 | Oct 26 17:11:53 SVRNAME systemd[1]: Starting PostgreSQL database server...
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| 25 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] FATAL: database files are incompatible with server
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| 26 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] DETAIL: The data directory was initialized by PostgreSQL version 13, which is not compatible with this version 14.0.
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| 27 | Oct 26 17:11:53 SRVNAME postgres[17336]: pg_ctl: could not start server
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| 28 | Oct 26 17:11:53 SRVNAME postgres[17336]: Examine the log output.
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| 29 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Control process exited, code=exited, status=1/FAILURE
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| 30 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Failed with result 'exit-code'.
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| 31 | Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.</screen>
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| 32 |
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| 33 | <para>
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| 34 | If you like to avoid those situations like the one above finding
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| 35 | your database server software refusing to start, it is highly
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| 36 | recommended to read the following thoughts about how to upgrade
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| 37 | a DBMS (Database Management System) prior to actually doing the
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| 38 | upgrade.
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| 39 | </para>
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| 40 | <para>
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| 41 | Even if you are installing a DBMS the initial time, read it
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| 42 | anyway, it might give you a guideline on how to set up backup
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| 43 | and restore procedures (at least the strategy for building
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| 44 | them) which are sufficient for your needs and for the safety
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| 45 | of your data.
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| 46 | </para>
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| 47 |
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| 48 | <sect2>
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| 49 | <title>Upgrade database server packages</title>
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| 50 |
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| 51 | <para>
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| 52 | Usually, DB systems work on a bunch of files which holds
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| 53 | the database metadata and the data itself. Those files
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| 54 | are highly optimized in their internal structures for use
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| 55 | by the server software. When upgrading such a server software,
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| 56 | it can happen that the server software expects a slightly
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| 57 | different file format than it has been created by previous
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| 58 | versions. In the best case, the new software can act on the
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| 59 | old format as well - while not benefitting from newer formats
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| 60 | which might result in better performance or of other improvements.
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| 61 | It can also happen that the new server software will reformat
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| 62 | the data files automatically at the first start.
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| 63 | </para>
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| 64 |
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| 65 | <para>
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| 66 | Unfortunatly, the most likly case is that the new server
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| 67 | software complains about invalid data file formats and exits.
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| 68 | When this happens and you have overwritten the installed server
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| 69 | software with the new one, you are kind of lost as you lsot the
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| 70 | software which can read the data files and the new software is
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| 71 | unwilling to do so.
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| 72 | </para>
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| 73 |
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| 74 | <para>
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| 75 | Changes in data file formats come usually beside major
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| 76 | version changes. But there is no guaranty. Before upgrading
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| 77 | the server software, check the documentation if there are
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| 78 | changes which will require a data file reformat.
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| 79 | </para>
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| 80 |
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| 81 | <para>
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| 82 | Of course, if you have databases with content which is not
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| 83 | easily to rebuild, it is always a good idea of creating backups
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| 84 | of the database from time to time. When going to upgrade the
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| 85 | server software, the time is quite good to run another backup.
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| 86 | </para>
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| 87 |
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| 88 | <sect3>
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| 89 | <title>Upgrade by backup and restore</title>
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| 90 |
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| 91 | <note>
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| 92 | <para>
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| 93 | A backup is meaningless if there is no verified process
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| 94 | to restore the data from this backup. When running a
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| 95 | database server, you should not only create backups but you
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| 96 | should also verify that the process you designed to fullfill
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| 97 | the restore task is working properly. When you encounter a
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| 98 | problem with the restore at the time you urgently have to
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| 99 | rely on the backup data, it is too late - your database are
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| 100 | in high danger at this moment.
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| 101 | </para>
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| 102 | </note>
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| 103 |
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| 104 | <para>
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| 105 | In general, most (all?) database server software provides
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| 106 | some basic tools to create backups of your data. Usually,
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| 107 | the backups created with those tools can be read by newer
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| 108 | versions of the software (here the restore tool). The other
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| 109 | way round (older resote tools can work with newer backup data)
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| 110 | is not defined and you should <emphasis>never</emphasis>
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| 111 | blindly assume that it would work. It might do, but usually
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| 112 | it doesn't.
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| 113 | </para>
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| 114 |
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| 115 | <para>
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| 116 | The most easiest way to upgrade your database files is to
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| 117 | </para>
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| 118 |
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| 119 | <itemizedlist>
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| 120 | <listitem>
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| 121 | <para>Create a full database backup using the old tools.</para>
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| 122 | <para>This step creates an offline copy of the database
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| 123 | files ready to be used for long term archiving, for desaster
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| 124 | recovery or just as a preparation for upgrade. This offline
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| 125 | backups consists of the full one-to-one copy of the current
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| 126 | database files or a backup of the files from a certain time
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| 127 | in history plus all journal data (that is Oracle(R)
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| 128 | terminology, its called "Continuous Archiving" or "write
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| 129 | ahead log (WAL)" in Postgresql) containing information about
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| 130 | changes made to the data content. The later are more quickly
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| 131 | to create if the DB software provides such kind of journal as
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| 132 | you only have to save the changes which are recorded in those
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| 133 | journals from the last backup upto now. The amount of data to
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| 134 | backup is much less than doing a full backup all the time.</para>
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| 135 | <para>In terms of upgrading a DB server software, it is
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| 136 | recommended to perform a full backup (which can be used for
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| 137 | subsequent incremental backups) but if the amount of data is
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| 138 | too big an incremental backup will be sufficient, too. Which
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| 139 | strategy is sufficient for you depends on the amount of data
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| 140 | stored in your DB (is it a few hundret of table rows or is it
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| 141 | hundrets of Terabyte. A full backup of the later one isn't done
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| 142 | quickly (and we assume that the underlaying system of such a DB
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| 143 | might not be a home brewed LFS anyhow).</para>
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| 144 | </listitem>
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| 145 | <listitem>
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| 146 | <para>Upgrade the server software</para>
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| 147 | <para>In this step, instructions to build the database
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| 148 | server software are executed just as they are shown in
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| 149 | subsequent sections talking about the DBMs like MariaDB or
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| 150 | Postgresql. This is building the software as
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| 151 | it is been done as usual in the BLFS book.</para>
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| 152 | </listitem>
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| 153 | <listitem>
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| 154 | <para>Restore the database by using the new tools.</para>
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| 155 | <para>To restore the data, the tools of the newly installed
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| 156 | server software is used. During the restore process, the new
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| 157 | tools will create and/or upgrade the data files in the
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| 158 | format the software expects them to be.</para>
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| 159 | </listitem>
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| 160 | </itemizedlist>
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| 161 |
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| 162 | <para>
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| 163 | Since you have already a backup procedure in place (and you
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| 164 | have tested your restore procedure, don't you?), this way might
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| 165 | be the easiest way to upgrade as you are going to use well-known
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| 166 | processes to upgrade just as you allways do - at least in terms
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| 167 | of the backup and restore.
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| 168 | </para>
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| 169 |
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| 170 | </sect3>
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| 171 |
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| 172 | <sect3>
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| 173 | <title>Upgrade by system tools</title>
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| 174 |
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| 175 | <para>
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| 176 | Some database systems (for instance Postgresql) provides
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| 177 | a tool which can reformat (=upgrade) the existing database
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| 178 | files to the new format. Since the upgrading tool has to
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| 179 | be used from the new server software (the old one cannot
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| 180 | know anything about a new file format), the old software
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| 181 | might be overwritten due to installation of the new software.
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| 182 | </para>
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| 183 |
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| 184 | <para>
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| 185 | In case you have to restore a backup (may be because running
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| 186 | the upgrade tool failed) you have to reinstall the old version
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| 187 | to get back the access to your data.
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| 188 | </para>
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| 189 |
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| 190 | <para>
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| 191 | Even though those tools might work one the actual database
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| 192 | files, it is still highly recommended to create a full backup
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| 193 | before running them. Any case of failure might result in a
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| 194 | serious damage of the database files.
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| 195 | </para>
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| 196 |
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| 197 | </sect3>
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| 198 |
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| 199 | </sect2>
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| 200 |
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| 201 | <sect2>
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| 202 | <title>Notes for specific DBMS</title>
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| 203 |
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| 204 | <sect3>
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| 205 | <title>PostgreSQL</title>
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| 206 |
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| 207 | <!-- might add some advanced notes for the DBMS here -->
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| 208 |
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| 209 | <para>Upstream documentation for Backup & Restore:
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| 210 | <ulink url="https://www.postgresql.org/docs/current/backup.html"/>
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| 211 | </para>
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| 212 |
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| 213 | </sect3>
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| 214 |
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| 215 | <sect3>
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| 216 | <title>MariaDB</title>
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| 217 |
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| 218 | <!-- might add some advanced notes for the DBMS here -->
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| 219 |
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| 220 | <para>Upstream documentation for Backup & Restore:
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| 221 | <ulink url="https://mariadb.com/kb/en/backup-and-restore-overview/"/>
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| 222 | </para>
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| 223 |
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| 224 | </sect3>
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| 225 |
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| 226 | </sect2>
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| 227 |
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| 228 | </sect1>
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