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>Important notes about upgrading Database Server Software</title>
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16 |
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17 | <note><para>This section is about reinstalling database software
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18 | when an existing database is in use. It is not applicable for
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19 | initial installations or if there is no existing database for
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20 | the package being updated, but users should read through it
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21 | to become aware of issues that can arise in the future.</para></note>
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22 |
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23 | <para>Lets start this chapter with a dramatic screenshot of an issue that
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24 | really happened. This issue will not occur if you are going to install the
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25 | software the first time:</para>
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26 |
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27 | <screen>$ sudo systemctl status postgresql
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28 | -- postgresql.service - PostgreSQL database server
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29 | Loaded: loaded (/usr/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
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30 | Active: failed (Result: exit-code) since Tue 2021-10-26 17:11:53 CDT; 2min 49s ago
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31 | Process: 17336 ExecStart=/usr/bin/pg_ctl -s -D ${PGROOT}/data start -w -t 120 (code=exited, status=1/FAILURE)
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32 | CPU: 7ms
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33 |
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34 | Oct 26 17:11:53 SVRNAME systemd[1]: Starting PostgreSQL database server...
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35 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] FATAL:
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36 | database files are incompatible with server
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37 | Oct 26 17:11:53 SRVNAME postgres[17338]: 2021-10-26 17:11:53.420 CDT [17338] DETAIL:
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38 | The data directory was initialized by PostgreSQL version 13,
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39 | which is not compatible with this version 14.0.
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40 | Oct 26 17:11:53 SRVNAME postgres[17336]: pg_ctl: could not start server
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41 | Oct 26 17:11:53 SRVNAME postgres[17336]: Examine the log output.
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42 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Control process exited, code=exited, status=1/FAILURE
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43 | Oct 26 17:11:53 SRVNAME systemd[1]: postgresql.service: Failed with result 'exit-code'.
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44 | Oct 26 17:11:53 SRVNAME systemd[1]: Failed to start PostgreSQL database server.</screen>
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45 |
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46 | <para>
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47 | To avoid situations like the one above finding your database server
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48 | software refusing to start, read the following thoughts about how to
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49 | upgrade a DBMS (Database Management System) prior to actually doing the
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50 | upgrade.
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51 | </para>
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52 |
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53 | <para>
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54 | The root cause of the issue shown above was an upgrade
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55 | of the server software to a newer major version but leaving the
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56 | data files untouched. The administrator was able to recover without any
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57 | loss of data.
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58 | </para>
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59 |
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60 | <para>
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61 | Even if you are doing an install DBMS install, read through this
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62 | section. Tt will provide you information about how to set up backup
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63 | and restore procedures (at least the strategy for building
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64 | them) which are sufficient for your needs and for the safety
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65 | of your data.
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66 | </para>
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67 |
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68 | <sect2>
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69 | <title>Upgrade database server packages</title>
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70 |
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71 | <para>
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72 | Database systems work on files which hold the database metadata and the
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73 | data itself. Those files are highly optimized in their internal
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74 | structures for use by the server software. When upgrading such server
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75 | software, newer server software may expect a different file format than
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76 | was created by previous versions. In the best case, the new software can
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77 | act on the old format as well—but not benefitting from newer
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78 | formats which might result in better performance or of other
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79 | improvements. It can also happen that the new server software will
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80 | reformat the data files automatically when starting.
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81 | </para>
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82 |
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83 | <para>
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84 | Unfortunatly, the most likly case is that the new server software
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85 | complains about out of date file formats and exits. When this happens
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86 | and you have overwritten the installed server software, you may not be
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87 | able to read the data files and the new software is unwilling to do so.
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88 | </para>
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89 |
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90 | <para>
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91 | Changes in data file formats usually happen at major version changes but
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92 | potentially can come at other times. Before upgrading the server
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93 | software, check the documentation if there are changes which will
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94 | require reformatting the database.
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95 | </para>
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96 |
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97 | <para>
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98 | Of course, if you have databases with content which is not easy to
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99 | rebuild, it is always a good idea to create backups of the database from
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100 | time to time. When upgrading the server software, it is time to run
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101 | another backup.
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102 | </para>
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103 |
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104 | <sect3>
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105 | <title>Upgrade by backup and restore</title>
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106 |
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107 | <note>
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108 | <para>
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109 | A backup is meaningless if there is no verified process
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110 | to restore the data from this backup. When running a
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111 | database server, you should not only create backups but you
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112 | should also verify that the process you designed to fullfill
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113 | the restore task is working properly. When you encounter a
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114 | problem with the restore when you urgently have to
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115 | rely on the backup data, it is too late—your database is
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116 | in danger.
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117 | </para>
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118 | </note>
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119 |
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120 | <para>
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121 | In general, most (all?) database server software provides some basic
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122 | tools to create backups of your data. Usually the backups created with
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123 | those tools can be read by newer versions of the software (via a
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124 | restore tool). Using older restore tools with newer backup data is not
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125 | defined and you should <emphasis>never</emphasis> blindly assume that
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126 | it will work. It might, but usually it doesn't.
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127 | </para>
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128 |
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129 | <para>
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130 | The easiest way to upgrade your database files is to
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131 | </para>
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132 |
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133 | <itemizedlist>
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134 | <listitem>
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135 | <para>Create a full database backup using the old tools.</para>
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136 |
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137 | <para>This step creates an offline copy of the database files ready
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138 | to be used for long term archiving, for disaster recovery, or just
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139 | preparation for upgrade. This offline backup consists of the full
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140 | one-to-one copy of the current database files or a backup of the
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141 | files from a certain time in history plus all journal data (that is
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142 | Oracle® terminology, it is called "Continuous Archiving" or
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143 | "write ahead log (WAL)" in Postgresql) containing information about
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144 | changes made to the data content. The later take less time to create
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145 | if the DB software provides this type of journaling as you only have
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146 | to save the changes after creating the last backup. The amount of
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147 | data to backup is much less than doing a full backup every
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148 | time.</para>
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149 |
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150 | <para>In terms of upgrading database server software, a full backup
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151 | (which can be used for subsequent incremental backups) should be
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152 | made, but if the amount of data is too big, an incremental backup will
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153 | be sufficient. Which strategy is appropriate for you depends on
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154 | the amount of data stored in your database (is it a few hundred table
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155 | rows or is it hundreds of terabytes?). A full backup of the later one
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156 | isn't done quickly (and we assume that the underlying system of such
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157 | a database is probably not on an LFS system). To close the last gap
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158 | to fully protect your data, create a backup of the corresponding old
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159 | binaries (and/or their sources) and store it along with the data
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160 | files to make sure that there is a fallback solution if
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161 | the newer software is not able to read the older data.</para>
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162 | </listitem>
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163 |
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164 | <listitem>
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165 | <para>Upgrade the server software</para>
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166 |
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167 | <para>In this step, instructions to build the database server
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168 | software are executed just as they are shown in subsequent sections
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169 | talking about the DBMs like MariaDB or Postgresql. That is, build
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170 | the software as usual using BLFS instructions.</para>
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171 | </listitem>
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172 |
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173 | <listitem>
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174 | <para>Restore the database by using the new tools.</para>
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175 |
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176 | <para>To restore the data, the tools of the newly installed server
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177 | software should be used. During the restoration process, the new
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178 | tools will create and/or upgrade the data files in the format the
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179 | software requires. It is assumed that newer software is capable of
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180 | reading old data.</para>
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181 | </listitem>
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182 | </itemizedlist>
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183 |
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184 | <para>
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185 | Since you have already have a backup procedure in place (and you
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186 | have tested your restore procedure, right?), this might
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187 | be the easiest way to upgrade as you are going to use your well known
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188 | processes to upgrade just as you allways do—at least in terms
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189 | of the backup and restore.
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190 | </para>
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191 |
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192 | </sect3>
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193 |
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194 | <sect3>
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195 | <title>Upgrade the database files by using system tools</title>
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196 |
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197 | <para>
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198 | Some database systems (for instance Postgresql) provide
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199 | a tool which can reformat (upgrade) the existing database
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200 | files to the new format. Since the upgrading tool has to
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201 | be used from the new server software (the old one cannot
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202 | know anything about a new file format), the old software
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203 | might be overwritten due to installation of the new software.
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204 | </para>
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205 |
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206 | <para>
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207 | In case you have to restore a backup (for example, running
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208 | the upgrade tool failed) you have to reinstall the old version
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209 | to get back the access to your data.
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210 | </para>
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211 |
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212 | <para>
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213 | Even though those tools might work with one of the actual database
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214 | files, you should create a full backup before running them. A failure
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215 | might result in a serious damage of the database files.
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216 | </para>
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217 |
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218 | </sect3>
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219 |
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220 | </sect2>
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221 |
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222 | <sect2>
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223 | <title>Notes for specific DBMS</title>
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224 |
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225 | <sect3>
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226 | <title>PostgreSQL</title>
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227 |
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228 | <!-- might add some advanced notes for the DBMS here -->
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229 |
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230 | <para>Upstream documentation for Backup/Restore:
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231 | <ulink url="https://www.postgresql.org/docs/current/backup.html"/>
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232 | </para>
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233 |
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234 | </sect3>
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235 |
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236 | <sect3>
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237 | <title>MariaDB</title>
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238 |
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239 | <!-- might add some advanced notes for the DBMS here -->
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240 |
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241 | <para>Upstream documentation for Backup/Restore:
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242 | <ulink url="https://mariadb.com/kb/en/backup-and-restore-overview/"/>
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243 | </para>
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244 |
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245 | </sect3>
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246 |
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247 | <sect3>
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248 | <title>Sqlite</title>
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249 |
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250 | <!-- might add some advanced notes for the DBMS here -->
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251 |
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252 | <para>Do not underestimate <application>Sqlite</application>. It is a
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253 | feature rich DBMS. The main difference from the two big players above is
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254 | that Sqlite does not provide access via a network API. Sqlite databases
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255 | are files always stored on the same machine as the running program which
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256 | uses the database. The manipulation of data content is done via API calls
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257 | to library functions directly within the program.</para>
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258 |
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259 | <para>In the upstream documentation you may find the following
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260 | useful:</para>
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261 |
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262 | <para>Documentation of the sqlite3 command line tool:
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263 | <ulink url="https://www.sqlite.org/cli.html"/>
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264 | </para>
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265 |
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266 | <para>Documentation of backup API calls:
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267 | <ulink url="https://www.sqlite.org/backup.html"/>
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268 | </para>
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269 |
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270 | <para>Unfortunatly, there is no dedicated chapter in the
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271 | upstream documentation talking about backup/restore but
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272 | there are several articles about it on the
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273 | Internet. One example is shown below.</para>
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274 |
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275 | <para>Documentation for Backup/Restore:
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276 | <ulink url="https://database.guide/backup-sqlite-database/"/>
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277 | </para>
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278 |
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279 | </sect3>
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280 |
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281 | <sect3>
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282 | <title>Berkeley DB</title>
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283 |
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284 | <!-- might add some advanced notes for the DBMS here -->
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285 |
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286 | <para>Just like <application>Sqlite</application> this
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287 | software acts on local database files meaning there is no
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288 | network interface.</para>
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289 |
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290 | <para>The relevant resources for Backup/Restore a Berkeley database
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291 | are the man pages for <filename>db_dump</filename> and its
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292 | counterpart <filename>db_load</filename>.</para>
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293 |
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294 | </sect3>
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295 | </sect2>
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296 |
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297 | </sect1>
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