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Clarified QuerySet.iterator()'s docs on server-side cursors.
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@ -43,11 +43,12 @@ div.nav { margin: 0; font-size: 11px; text-align: right; color: #487858;}
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/*** basic styles ***/
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/*** basic styles ***/
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dd { margin-left:15px; }
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dd { margin-left:15px; }
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h1,h2,h3,h4 { margin-top:1em; font-family:"Trebuchet MS",sans-serif; font-weight:normal; }
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h1,h2,h3,h4,h5 { margin-top:1em; font-family:"Trebuchet MS",sans-serif; font-weight:normal; }
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h1 { font-size:218%; margin-top:0.6em; margin-bottom:.4em; line-height:1.1em; }
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h1 { font-size:218%; margin-top:0.6em; margin-bottom:.4em; line-height:1.1em; }
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h2 { font-size:175%; margin-bottom:.6em; line-height:1.2em; color:#092e20; }
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h2 { font-size:175%; margin-bottom:.6em; line-height:1.2em; color:#092e20; }
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h3 { font-size:150%; font-weight:bold; margin-bottom:.2em; color:#487858; }
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h3 { font-size:150%; font-weight:bold; margin-bottom:.2em; color:#487858; }
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h4 { font-size:125%; font-weight:bold; margin-top:1.5em; margin-bottom:3px; }
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h4 { font-size:125%; font-weight:bold; margin-top:1.5em; margin-bottom:3px; }
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h5 { font-size:110%; font-weight:bold; margin-top:1em; margin-bottom:3px; }
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div.figure { text-align: center; }
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div.figure { text-align: center; }
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div.figure p.caption { font-size:1em; margin-top:0; margin-bottom:1.5em; color: #555;}
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div.figure p.caption { font-size:1em; margin-top:0; margin-bottom:1.5em; color: #555;}
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hr { color:#ccc; background-color:#ccc; height:1px; border:0; }
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hr { color:#ccc; background-color:#ccc; height:1px; border:0; }
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@ -2021,15 +2021,32 @@ evaluated will force it to evaluate again, repeating the query.
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Also, use of ``iterator()`` causes previous ``prefetch_related()`` calls to be
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Also, use of ``iterator()`` causes previous ``prefetch_related()`` calls to be
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ignored since these two optimizations do not make sense together.
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ignored since these two optimizations do not make sense together.
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Some Python database drivers still load the entire result set into memory, but
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Depending on the database backend, query results will either be loaded all at
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won't cache results after iterating over them. Oracle and :ref:`PostgreSQL
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once or streamed from the database using server-side cursors.
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<postgresql-server-side-cursors>` use server-side cursors to stream results
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from the database without loading the entire result set into memory.
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With server-side cursors
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^^^^^^^^^^^^^^^^^^^^^^^^
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Oracle and :ref:`PostgreSQL <postgresql-server-side-cursors>` use server-side
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cursors to stream results from the database without loading the entire result
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set into memory.
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The Oracle database driver always uses server-side cursors.
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On PostgreSQL, server-side cursors will only be used when the
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On PostgreSQL, server-side cursors will only be used when the
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:setting:`DISABLE_SERVER_SIDE_CURSORS <DATABASE-DISABLE_SERVER_SIDE_CURSORS>`
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:setting:`DISABLE_SERVER_SIDE_CURSORS <DATABASE-DISABLE_SERVER_SIDE_CURSORS>`
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setting is ``False``. Read :ref:`transaction-pooling-server-side-cursors` if
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setting is ``False``. Read :ref:`transaction-pooling-server-side-cursors` if
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you're using a connection pooler configured in transaction pooling mode.
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you're using a connection pooler configured in transaction pooling mode. When
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server-side cursors are disabled, the behavior is the same as databases that
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don't support server-side cursors.
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Without server-side cursors
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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MySQL and SQLite don't support streaming results, hence the Python database
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drivers load the entire result set into memory. The result set is then
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transformed into Python row objects by the database adapter using the
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``fetchmany()`` method defined in :pep:`249`.
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.. versionchanged:: 1.11
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.. versionchanged:: 1.11
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