https://www.memcp.org/index.php?action=history&feed=atom&title=Databases%2C_Tables_and_Columns 2026-09-19T11:34:50Z Revision history for this page on the wiki MediaWiki 1.39.1 https://www.memcp.org/index.php?title=Databases,_Tables_and_Columns&diff=325&oldid=prev 2026-08-28T09:59:27Z

<p>Refresh MemCP documentation: accuracy, operational guidance, performance profile and maintained API reference</p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 11:59, 28 August 2026</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1">Line 1:</td> <td colspan="2" class="diff-lineno">Line 1:</td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* MemCP has </del>a data <del style="font-weight: bold; text-decoration: none;">folder which defaults </del>to <del style="font-weight: bold; text-decoration: none;">&quot;</del>.<del style="font-weight: bold; text-decoration: none;">/data&quot;</del>. <del style="font-weight: bold; text-decoration: none;">Every subdirectory of that folder is </del>a <del style="font-weight: bold; text-decoration: none;">database</del>.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">&lt;!-- Copyright (C) 2026 Carl-Philip Haensch --&gt;</ins></div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* Databases consist </del>of <del style="font-weight: bold; text-decoration: none;">tables</del></div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">&lt;!-- SPDX-License-Identifier: GPL-3.0-or-later --&gt;</ins></div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* Tables consist of </del>columns <del style="font-weight: bold; text-decoration: none;">and </del>[[Shards, RecordIDs, Main Storage, Delta Storage<del style="font-weight: bold; text-decoration: none;">|shards</del>]]</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">= Databases, Tables and Columns =</ins></div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* Columns have a name</del>, <del style="font-weight: bold; text-decoration: none;">a type</del>, <del style="font-weight: bold; text-decoration: none;">type dimensions</del></div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">* Some columns can be &quot;computed columns&quot; that are not filled by INSERT values but rather computed from an expression</del></div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">A database is </ins>a <ins style="font-weight: bold; text-decoration: none;">catalog entry and namespace. With the local backend it normally corresponds to a directory below the configured </ins>data <ins style="font-weight: bold; text-decoration: none;">path. A JSON backend configuration can instead map it </ins>to <ins style="font-weight: bold; text-decoration: none;">S3-compatible object storage or optional Ceph/RADOS.</ins></div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">A table contains its logical schema and one or more shards</ins>. <ins style="font-weight: bold; text-decoration: none;">Ordinary columns have stored values; computed and order-dependent columns have logical definitions whose physical caches may be created, repaired, invalidated, or evicted</ins>. <ins style="font-weight: bold; text-decoration: none;">SQL views store </ins>a <ins style="font-weight: bold; text-decoration: none;">SELECT definition and are expanded before logical planning</ins>.</div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">Each table selects one </ins>of <ins style="font-weight: bold; text-decoration: none;">the &lt;code&gt;safe&lt;/code&gt;, &lt;code&gt;logged&lt;/code&gt;, &lt;code&gt;sloppy&lt;/code&gt;, &lt;code&gt;memory&lt;/code&gt;, or reconstructible &lt;code&gt;cache&lt;/code&gt; engines. This changes durability and eviction semantics, not the SQL column types. See [[Persistency and Performance Guarantees]] before changing an existing table&#039;s ENGINE.</ins></div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">Primary, unique, and adaptive secondary indexes are represented separately from the column values. User and hidden triggers enforce constraints or maintain derived structures. Physical scans obtain shard access and read </ins>columns <ins style="font-weight: bold; text-decoration: none;">in batches; application code should use SQL rather than depending on internal shard or record-ID representation.</ins></div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">See </ins>[[Shards, RecordIDs, Main Storage, Delta Storage]], <ins style="font-weight: bold; text-decoration: none;">[[Columnar Storage]]</ins>, <ins style="font-weight: bold; text-decoration: none;">and [[Storage Backends]].</ins></div></td></tr> <!-- diff cache key memcp_wiki-mediawiki-:diff::1.12:old-60:rev-325 --> </table>

Wikiservice https://www.memcp.org/index.php?title=Databases,_Tables_and_Columns&diff=60&oldid=prev 2024-05-17T20:26:05Z

<p></p> <table style="background-color: #fff; color: #202122;" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="en"> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td> <td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 22:26, 17 May 2024</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l2">Line 2:</td> <td colspan="2" class="diff-lineno">Line 2:</td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Databases consist of tables</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Databases consist of tables</div></td></tr> <tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Tables consist of columns and [[Shards, RecordIDs, Main Storage, Delta Storage|shards]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* Tables consist of columns and [[Shards, RecordIDs, Main Storage, Delta Storage|shards]]</div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">* Columns have a name, a type, type dimensions</ins></div></td></tr> <tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">* Some columns can be "computed columns" that are not filled by INSERT values but rather computed from an expression</ins></div></td></tr> <!-- diff cache key memcp_wiki-mediawiki-:diff::1.12:old-32:rev-60 --> </table>

Carli https://www.memcp.org/index.php?title=Databases,_Tables_and_Columns&diff=32&oldid=prev 2024-05-17T07:20:29Z

<p>Created page with &quot;* MemCP has a data folder which defaults to &quot;./data&quot;. Every subdirectory of that folder is a database. * Databases consist of tables * Tables consist of columns and <a href="/wiki/Shards,_RecordIDs,_Main_Storage,_Delta_Storage" title="Shards, RecordIDs, Main Storage, Delta Storage">shards</a>&quot;</p> <p><b>New page</b></p><div>* MemCP has a data folder which defaults to &quot;./data&quot;. Every subdirectory of that folder is a database.<br /> * Databases consist of tables<br /> * Tables consist of columns and [[Shards, RecordIDs, Main Storage, Delta Storage|shards]]</div>

Carli