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From: Tom Lane <[email protected]>
To: Julien Rouhaud <[email protected]>
Cc: Tatsuo Ishii <[email protected]>
Cc: [email protected]
Subject: Re: Typo in perform.sgml?
Date: Sat, 07 Dec 2019 15:56:39 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<CAOBaU_afRuoGf40O0YN_ncZ5L5pEXF8HaUXJ6A_S3XgOJWH5Dw@mail.gmail.com>
	<[email protected]>

I wrote:
> Actually, that whole para could do with a rewrite; whoever wrote
> it was obviously not familiar with Strunk & White's dictum
> "Omit needless words".

Looking closer, there were also some unnecessary inconsistencies with
the rest of the section, such as use of "records" rather than "rows",
and different markup choices.  I propose the attached ... it's
actually a bit longer than the original, but that's because it
offers more details.

			regards, tom lane



Attachments:

  [text/x-diff] improve-subplan-pruning-docs.patch (1.6K, 2-improve-subplan-pruning-docs.patch)
  download | inline diff:
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index 715aff6..0f61b09 100644
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -896,15 +896,16 @@ EXPLAIN ANALYZE SELECT * FROM tenk1 WHERE unique1 &lt; 100 AND unique2 &gt; 9000
    </para>
 
    <para>
-    Generally, the <command>EXPLAIN</command> output will display details for
-    every plan node which was generated by the query planner.  However, there
-    are cases where the executor is able to determine that certain nodes are
-    not required; currently, the only node types to support this are the
-    <literal>Append</literal> and <literal>MergeAppend</literal> nodes.  These
-    node types have the ability to discard subnodes which they are able to
-    determine won't contain any records required by the query.  It is possible
-    to determine that nodes have been removed in this way by the presence of a
-    "Subplans Removed" property in the <command>EXPLAIN</command> output.
+    Normally, <command>EXPLAIN</command> will display every plan node
+    created by the planner.  However, there are cases where the executor
+    can determine that certain nodes need not be executed because they
+    cannot produce any rows, based on parameter values that were not
+    available at planning time.  (Currently this can only happen for child
+    nodes of an Append or MergeAppend node that is scanning a partitioned
+    table.)  When this happens, those plan nodes are omitted from
+    the <command>EXPLAIN</command> output and a <literal>Subplans
+    Removed: <replaceable>N</replaceable></literal> annotation appears
+    instead.
    </para>
   </sect2>
 

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