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Commit2a5ecb5

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Update documentation to mention huge pages on other OSes
Previously, the docs implied that only Linux and Windows could use hugepages. That's not quite true: it's just that we only know how torequest them explicitly on those OSes. Be more explicit about whathuge_pages really does and mention that some OSes may use huge pagesautomatically.Author: Thomas Munro and Catalin IacobReviewed-By: Justin Pryzby, Peter EisentrautDiscussion:https://postgr.es/m/CAEepm=3qzR-hfjepymohuC4XO5phxoSoipOjm6BEhnJHjNR+jg@mail.gmail.com
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‎doc/src/sgml/config.sgml

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@@ -1372,14 +1372,20 @@ include_dir 'conf.d'
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</term>
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<listitem>
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<para>
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Enables/disables the use of huge memory pages. Valid values are
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<literal>try</literal> (the default), <literal>on</literal>,
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and <literal>off</literal>.
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Controls whether huge pages are requested for the main shared memory
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area. Valid values are <literal>try</literal> (the default),
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<literal>on</literal>, and <literal>off</literal>. With
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<varname>huge_pages</varname> set to <literal>try</literal>, the
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server will try to request huge pages, but fall back to the default if
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that fails. With <literal>on</literal>, failure to request huge pages
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will prevent the server from starting up. With <literal>off</literal>,
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huge pages will not be requested.
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</para>
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<para>
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At present, this feature is supported only on Linux and Windows. The
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setting is ignored on other systems when set to <literal>try</literal>.
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At present, this setting is supported only on Linux and Windows. The
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setting is ignored on other systems when set to
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<literal>try</literal>.
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</para>
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<para>
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</para>
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<para>
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With <varname>huge_pages</varname> set to <literal>try</literal>,
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the server will try to use huge pages, but fall back to using
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normal allocation if that fails. With <literal>on</literal>, failure
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to use huge pages will prevent the server from starting up. With
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<literal>off</literal>, huge pages will not be used.
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Note that this setting only affects the main shared memory area.
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Operating systems such as Linux, FreeBSD, and Illumos can also use
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huge pages (also known as <quote>super</quote> pages or
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<quote>large</quote> pages) automatically for normal memory
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allocation, without an explicit request from
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<productname>PostgreSQL</productname>. On Linux, this is called
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<quote>transparent huge pages</quote><indexterm><primary>transparent
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huge pages</primary></indexterm> (THP). That feature has been known to
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cause performance degradation with
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<productname>PostgreSQL</productname> for some users on some Linux
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versions, so its use is currently discouraged (unlike explicit use of
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<varname>huge_pages</varname>).
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</para>
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</listitem>
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</varlistentry>

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