[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 |
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[fe9a4337] | 12 | <title>Important Notes About Upgrading Database Server Software</title>
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[7f6bf79b] | 13 |
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[d86ea4b] | 14 | <note><para>This section is about reinstalling database software
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| 15 | when an existing database is in use. It is not applicable for
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| 16 | initial installations or if there is no existing database for
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[7a9a7b26] | 17 | the package being updated, but users should read through it
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[b3ba4f9] | 18 | to become aware of issues that can arise in the future.</para></note>
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[d86ea4b] | 19 |
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[fe9a4337] | 20 | <para>Let's start this chapter with a dramatic screenshot of an error that
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| 21 | really happened. This error will not occur if you are installing database
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| 22 | software for the first time:</para>
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[bcdfc53] | 23 |
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| 24 | <screen>$ sudo systemctl status postgresql
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| 25 | -- postgresql.service - PostgreSQL database server
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| 26 | Loaded: loaded (/usr/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
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| 27 | Active: failed (Result: exit-code) since Tue 2021-10-26 17:11:53 CDT; 2min 49s ago
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| 28 | Process: 17336 ExecStart=/usr/bin/pg_ctl -s -D ${PGROOT}/data start -w -t 120 (code=exited, status=1/FAILURE)
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| 29 | CPU: 7ms
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| 30 |
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| 31 | Oct 26 17:11:53 SVRNAME systemd[1]: Starting PostgreSQL database server...
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[7a9a7b26] | 32 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] FATAL:
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[d86ea4b] | 33 | database files are incompatible with server
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[7a9a7b26] | 34 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] DETAIL:
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[d86ea4b] | 35 | The data directory was initialized by PostgreSQL version 13,
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| 36 | which is not compatible with this version 14.0.
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[bcdfc53] | 37 | Oct 26 17:11:53 SRVNAME postgres[17336]: pg_ctl: could not start server
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| 38 | Oct 26 17:11:53 SRVNAME postgres[17336]: Examine the log output.
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| 39 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Control process exited, code=exited, status=1/FAILURE
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| 40 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Failed with result 'exit-code'.
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| 41 | Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.</screen>
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| 42 |
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| 43 | <para>
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[fe9a4337] | 44 | To avoid situations like this (i.e., your database server
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| 45 | software refuses to start), read the following discussion of the best way to
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| 46 | upgrade a DBMS (Database Management System).
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[bcdfc53] | 47 | </para>
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[d86ea4b] | 48 |
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[bcdfc53] | 49 | <para>
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[fe9a4337] | 50 | The root cause of the error shown above was an upgrade
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| 51 | of the server software to a newer major version which left the
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| 52 | data files untouched. In this case, the administrator was able to recover
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| 53 | the DBMS without any loss of data.
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[7f6bf79b] | 54 | </para>
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[d86ea4b] | 55 |
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[7f6bf79b] | 56 | <para>
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[a1743b1] | 57 | Even if you are doing an initial DBMS install, read through this
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[fe9a4337] | 58 | section. It provides information about implementing backup
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| 59 | and restore procedures (or at least a strategy for creating
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| 60 | them) which will satisfy your needs and guarantee the safety
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[bcdfc53] | 61 | of your data.
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| 62 | </para>
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[8986fa9] | 63 |
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[bcdfc53] | 64 | <sect2>
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[fe9a4337] | 65 | <title>Upgrade Database Server Packages</title>
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[bcdfc53] | 66 |
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| 67 | <para>
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[d86ea4b] | 68 | Database systems work on files which hold the database metadata and the
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[fe9a4337] | 69 | data itself. The internal structure of these files is optimized for use
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| 70 | by the server software. When such server software is upgraded,
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| 71 | the new software may utilize a different file format than
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| 72 | had previously been used. Sometimes the new software can
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[a1743b1] | 73 | work with the old format as well as the new one—but without the
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[fe9a4337] | 74 | performance improvements the new format provides.
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| 75 | Other times, the new server software will
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| 76 | reformat the data files automatically after the upgrade.
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[bcdfc53] | 77 | </para>
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| 78 |
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| 79 | <para>
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[b9c353b] | 80 | Unfortunately, the most likely case is that the new server software
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[fe9a4337] | 81 | complains about out of date file formats and exits. When this happens,
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| 82 | and you have overwritten the old server software, you may end up
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| 83 | with a broken system and lost data.
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[bcdfc53] | 84 | </para>
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| 85 |
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| 86 | <para>
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[fe9a4337] | 87 | Changes in data file formats usually happen at major version changes, but
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| 88 | they can also occur at other times. Before upgrading any DBMS
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| 89 | software, check the documentation to see if this upgrade makes changes which
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[d86ea4b] | 90 | require reformatting the database.
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[bcdfc53] | 91 | </para>
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| 92 |
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| 93 | <para>
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[fe9a4337] | 94 | Of course, if you have databases with content that is not easily
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| 95 | rebuilt, it is always a good idea to create backups of the database from
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| 96 | time to time. Before upgrading the server software, you should run
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[d86ea4b] | 97 | another backup.
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[bcdfc53] | 98 | </para>
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| 99 |
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| 100 | <sect3>
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[fe9a4337] | 101 | <title>Upgrade by Backup and Restore</title>
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[bcdfc53] | 102 |
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| 103 | <note>
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| 104 | <para>
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[fe9a4337] | 105 | A backup is useless if there is no verified process
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[bcdfc53] | 106 | to restore the data from this backup. When running a
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[fe9a4337] | 107 | database server, you should not only create backups; you
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| 108 | should also verify that the restore process
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| 109 | really works. The time to test the restore procedure
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| 110 | is <emphasis>before</emphasis> you urgently need
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| 111 | to recover lost data.
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[bcdfc53] | 112 | </para>
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| 113 | </note>
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| 114 |
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| 115 | <para>
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[fe9a4337] | 116 | Most database server software provides some basic
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[d86ea4b] | 117 | tools to create backups of your data. Usually the backups created with
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| 118 | those tools can be read by newer versions of the software (via a
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[54d58907] | 119 | restore tool). Using older restore tools with newer backup data is
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[fe9a4337] | 120 | a bad idea; you should <emphasis>never</emphasis> blindly assume that
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[d86ea4b] | 121 | it will work. It might, but usually it doesn't.
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[bcdfc53] | 122 | </para>
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| 123 |
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| 124 | <para>
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[d86ea4b] | 125 | The easiest way to upgrade your database files is to
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[bcdfc53] | 126 | </para>
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| 127 |
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| 128 | <itemizedlist>
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[4e207bb] | 129 | <listitem>
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[bcdfc53] | 130 | <para>Create a full database backup using the old tools.</para>
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[7a9a7b26] | 131 |
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[fe9a4337] | 132 | <para>This step creates an offline copy of the database files—for
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| 133 | long term archiving, for disaster recovery, or as
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| 134 | preparation for an upgrade. This offline backup consists of either (1) a full
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| 135 | one-to-one copy of the current database files, or (2) a full backup of the
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| 136 | database files from a certain point in time, plus all the journal data (that is
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[d86ea4b] | 137 | Oracle® terminology, it is called "Continuous Archiving" or
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[fe9a4337] | 138 | "write ahead log (WAL)" in Postgresql) describing the
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| 139 | changes made after that point in time. This second form takes less time to create
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| 140 | (if the DB software provides this type of journaling) because you only have
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| 141 | to save the data that have changed since the last full backup was created.</para>
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| 142 |
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| 143 | <para>When upgrading database server software, a full backup
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[d86ea4b] | 144 | (which can be used for subsequent incremental backups) should be
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[fe9a4337] | 145 | created; but if there is a lot of data, an incremental backup will
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| 146 | suffice. The best strategy for you depends on
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[d86ea4b] | 147 | the amount of data stored in your database (is it a few hundred table
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[fe9a4337] | 148 | rows, or is it hundreds of terabytes?). A full backup in the latter case
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[54d58907] | 149 | can't be done quickly. To
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[fe9a4337] | 150 | fully protect your data, create a backup of the old
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| 151 | programs (and/or their sources) and save it, along with the data
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| 152 | files, to be certain there is a fallback solution if
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| 153 | the new software cannot read the old data.</para>
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[7a9a7b26] | 154 | </listitem>
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[d86ea4b] | 155 |
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[7a9a7b26] | 156 | <listitem>
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| 157 | <para>Upgrade the server software</para>
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[d86ea4b] | 158 |
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| 159 | <para>In this step, instructions to build the database server
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| 160 | software are executed just as they are shown in subsequent sections
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| 161 | talking about the DBMs like MariaDB or Postgresql. That is, build
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[7a9a7b26] | 162 | the software as usual using BLFS instructions.</para>
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| 163 | </listitem>
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[d86ea4b] | 164 |
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[7a9a7b26] | 165 | <listitem>
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| 166 | <para>Restore the database by using the new tools.</para>
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[d86ea4b] | 167 |
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| 168 | <para>To restore the data, the tools of the newly installed server
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| 169 | software should be used. During the restoration process, the new
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| 170 | tools will create and/or upgrade the data files in the format the
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[fe9a4337] | 171 | new software requires. It is assumed that newer software is capable of
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[d86ea4b] | 172 | reading old data.</para>
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[7a9a7b26] | 173 | </listitem>
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[d86ea4b] | 174 | </itemizedlist>
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[bcdfc53] | 175 |
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| 176 | <para>
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[fe9a4337] | 177 | Since you already have a backup procedure in place (and you
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[d86ea4b] | 178 | have tested your restore procedure, right?), this might
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[fe9a4337] | 179 | be the easiest way to upgrade as you can use your well known
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[5f729f8] | 180 | processes to upgrade just as you always do—at least in terms
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[bcdfc53] | 181 | of the backup and restore.
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| 182 | </para>
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| 183 |
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| 184 | </sect3>
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| 185 |
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| 186 | <sect3>
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[fe9a4337] | 187 | <title>Upgrade the Database Files by Using System Tools</title>
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[bcdfc53] | 188 |
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| 189 | <para>
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[d86ea4b] | 190 | Some database systems (for instance Postgresql) provide
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| 191 | a tool which can reformat (upgrade) the existing database
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[54d58907] | 192 | files to the new format.
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[fe9a4337] | 193 | If you need to restore from a backup (for example, running
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| 194 | the upgrade tool failed) you will have to reinstall the old software
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| 195 | to recover your data.
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[bcdfc53] | 196 | </para>
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| 197 |
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| 198 | <para>
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[fe9a4337] | 199 | Even though the reformatting tools might work as advertised,
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| 200 | you should create a full backup before running them. A failure
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| 201 | could cause serious damage to the database.
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[bcdfc53] | 202 | </para>
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| 203 |
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| 204 | </sect3>
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| 205 |
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| 206 | </sect2>
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| 207 |
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| 208 | <sect2>
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[fe9a4337] | 209 | <title>Notes for Specific DBMS</title>
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[8986fa9] | 210 |
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[bcdfc53] | 211 | <sect3>
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| 212 | <title>PostgreSQL</title>
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[8986fa9] | 213 |
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[bcdfc53] | 214 | <!-- might add some advanced notes for the DBMS here -->
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| 215 |
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[d86ea4b] | 216 | <para>Upstream documentation for Backup/Restore:
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[bcdfc53] | 217 | <ulink url="https://www.postgresql.org/docs/current/backup.html"/>
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| 218 | </para>
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[8986fa9] | 219 |
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[bcdfc53] | 220 | </sect3>
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| 221 |
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| 222 | <sect3>
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| 223 | <title>MariaDB</title>
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[8986fa9] | 224 |
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[bcdfc53] | 225 | <!-- might add some advanced notes for the DBMS here -->
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| 226 |
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[d86ea4b] | 227 | <para>Upstream documentation for Backup/Restore:
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[bcdfc53] | 228 | <ulink url="https://mariadb.com/kb/en/backup-and-restore-overview/"/>
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| 229 | </para>
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[8986fa9] | 230 |
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| 231 | </sect3>
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| 232 |
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| 233 | <sect3>
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| 234 | <title>Sqlite</title>
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| 235 |
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| 236 | <!-- might add some advanced notes for the DBMS here -->
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| 237 |
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[d86ea4b] | 238 | <para>Do not underestimate <application>Sqlite</application>. It is a
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[fe9a4337] | 239 | feature-rich DBMS. The main difference from the two big players above is
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[d86ea4b] | 240 | that Sqlite does not provide access via a network API. Sqlite databases
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[fe9a4337] | 241 | are always stored on the machine running the program which
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[d86ea4b] | 242 | uses the database. The manipulation of data content is done via API calls
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[8986fa9] | 243 | to library functions directly within the program.</para>
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| 244 |
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[d86ea4b] | 245 | <para>In the upstream documentation you may find the following
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| 246 | useful:</para>
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[8986fa9] | 247 |
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| 248 | <para>Documentation of the sqlite3 command line tool:
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| 249 | <ulink url="https://www.sqlite.org/cli.html"/>
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| 250 | </para>
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[d86ea4b] | 251 |
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[8986fa9] | 252 | <para>Documentation of backup API calls:
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| 253 | <ulink url="https://www.sqlite.org/backup.html"/>
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| 254 | </para>
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| 255 |
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[2c87187] | 256 | <para>Unfortunately, there is no dedicated chapter in the
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[fe9a4337] | 257 | upstream documentation talking about backup/restore, but
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[d86ea4b] | 258 | there are several articles about it on the
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[fe9a4337] | 259 | Internet. Here is an example.</para>
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[8986fa9] | 260 |
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[d86ea4b] | 261 | <para>Documentation for Backup/Restore:
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[8986fa9] | 262 | <ulink url="https://database.guide/backup-sqlite-database/"/>
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| 263 | </para>
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| 264 |
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[bcdfc53] | 265 | </sect3>
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| 266 |
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[8986fa9] | 267 | <sect3>
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| 268 | <title>Berkeley DB</title>
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| 269 |
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| 270 | <!-- might add some advanced notes for the DBMS here -->
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| 271 |
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[fe9a4337] | 272 | <para>Like <application>Sqlite</application>, this
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| 273 | software acts on local database files; there is no
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[d86ea4b] | 274 | network interface.</para>
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[8986fa9] | 275 |
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[fe9a4337] | 276 | <para>The relevant resources to back up/restore a Berkeley database
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[8986fa9] | 277 | are the man pages for <filename>db_dump</filename> and its
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| 278 | counterpart <filename>db_load</filename>.</para>
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| 279 |
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| 280 | </sect3>
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[bcdfc53] | 281 | </sect2>
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[8986fa9] | 282 |
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[bcdfc53] | 283 | </sect1>
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