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     <h1 class="title">
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      Chapter 16 MySQL Data Dictionary
     </h1>
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  <div class="toc">
   <p>
    <b>
     Table of Contents
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   <dl class="toc">
    <dt>
     <span class="section">
      <a href="data-dictionary-schema.html">
       16.1 Data Dictionary Schema
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-file-removal.html">
       16.2 Removal of File-based Metadata Storage
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-transactional-storage.html">
       16.3 Transactional Storage of Dictionary Data
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-object-cache.html">
       16.4 Dictionary Object Cache
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-information-schema.html">
       16.5 INFORMATION_SCHEMA and Data Dictionary Integration
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="serialized-dictionary-information.html">
       16.6 Serialized Dictionary Information (SDI)
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-usage-differences.html">
       16.7 Data Dictionary Usage Differences
      </a>
     </span>
    </dt>
    <dt>
     <span class="section">
      <a href="data-dictionary-limitations.html">
       16.8 Data Dictionary Limitations
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    </dt>
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  <p>
   MySQL Server incorporates a transactional data dictionary that
    stores information about database objects. In previous MySQL
    releases, dictionary data was stored in metadata files,
    nontransactional tables, and storage engine-specific data
    dictionaries.
  </p>
  <p>
   This chapter describes the main features, benefits, usage
    differences, and limitations of the data dictionary. For other
    implications of the data dictionary feature, refer to the
   <span class="quote">
    “
    <span class="quote">
     Data Dictionary Notes
    </span>
    ”
   </span>
   section in the
   <a class="ulink" href="/doc/relnotes/mysql/8.4/en/" target="_top">
    MySQL 8.4
    Release Notes
   </a>
   .
  </p>
  <p>
   Benefits of the MySQL data dictionary include:
  </p>
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    <li class="listitem">
     <p>
      Simplicity of a centralized data dictionary schema that
        uniformly stores dictionary data. See
      <a class="xref" href="data-dictionary-schema.html" title="16.1 Data Dictionary Schema">
       Section 16.1, “Data Dictionary Schema”
      </a>
      .
     </p>
    </li>
    <li class="listitem">
     <p>
      Removal of file-based metadata storage. See
      <a class="xref" href="data-dictionary-file-removal.html" title="16.2 Removal of File-based Metadata Storage">
       Section 16.2, “Removal of File-based Metadata Storage”
      </a>
      .
     </p>
    </li>
    <li class="listitem">
     <p>
      Transactional, crash-safe storage of dictionary data. See
      <a class="xref" href="data-dictionary-transactional-storage.html" title="16.3 Transactional Storage of Dictionary Data">
       Section 16.3, “Transactional Storage of Dictionary Data”
      </a>
      .
     </p>
    </li>
    <li class="listitem">
     <p>
      Uniform and centralized caching for dictionary objects. See
      <a class="xref" href="data-dictionary-object-cache.html" title="16.4 Dictionary Object Cache">
       Section 16.4, “Dictionary Object Cache”
      </a>
      .
     </p>
    </li>
    <li class="listitem">
     <p>
      A simpler and improved implementation for some
      <a class="link" href="information-schema.html" title="Chapter 28 INFORMATION_SCHEMA Tables">
       <code class="literal">
        INFORMATION_SCHEMA
       </code>
      </a>
      tables. See
      <a class="xref" href="data-dictionary-information-schema.html" title="16.5 INFORMATION_SCHEMA and Data Dictionary Integration">
       Section 16.5, “INFORMATION_SCHEMA and Data Dictionary Integration”
      </a>
      .
     </p>
    </li>
    <li class="listitem">
     <p>
      Atomic DDL. See
      <a class="xref" href="atomic-ddl.html" title="15.1.1 Atomic Data Definition Statement Support">
       Section 15.1.1, “Atomic Data Definition Statement Support”
      </a>
      .
     </p>
    </li>
   </ul>
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  <div class="important" style="margin-left: 0.5in; margin-right: 0.5in;">
   <div class="admon-title">
    Important
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   <p>
    A data dictionary-enabled server entails some general operational
      differences compared to a server that does not have a data
      dictionary; see
    <a class="xref" href="data-dictionary-usage-differences.html" title="16.7 Data Dictionary Usage Differences">
     Section 16.7, “Data Dictionary Usage Differences”
    </a>
    . Also, for
      upgrades to MySQL 8.0, the upgrade procedure differs somewhat from
      previous MySQL releases and requires that you verify the upgrade
      readiness of your installation by checking specific prerequisites.
      For more information, see
    <a class="xref" href="upgrading.html" title="Chapter 3 Upgrading MySQL">
     Chapter 3,
     <i>
      Upgrading MySQL
     </i>
    </a>
    ,
      particularly
    <a class="xref" href="upgrade-prerequisites.html" title="3.6 Preparing Your Installation for Upgrade">
     Section 3.6, “Preparing Your Installation for Upgrade”
    </a>
    .
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