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Re-allow testing of GiST buffered builds.

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Commit 16fa9b2b3 broke the ability to reliably test GiST buffered builds,
because it caused sorted builds to be done instead if sortsupport is
available, regardless of any attempt to override that.  While a would-be
test case could try to work around that by choosing an opclass that has
no sortsupport function, coverage would be silently lost the moment
someone decides it'd be a good idea to add a sortsupport function.

Hence, rearrange the logic in gistbuild() so that if "buffering = on"
is specified in CREATE INDEX, we will use that method, sortsupport or no.

Also document the interaction between sorting and the buffering
parameter, as 16fa9b2b3 failed to do.

(Note that in fact we still lack any test coverage of buffered builds,
but this is a prerequisite to adding a non-fragile test.)

Discussion: https://postgr.es/m/3249980.1602532990@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2020-10-12 17:09:50 -04:00
parent 397ea901e8
commit 78c0b6ed27
3 changed files with 77 additions and 53 deletions
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12
doc/src/sgml/ref/create_index.sgml
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@@ -463,11 +463,15 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
</term>
<listitem>
<para>
Determines whether the buffering build technique described in
Determines whether the buffered build technique described in
<xref linkend="gist-buffering-build"/> is used to build the index. With
<literal>OFF</literal> it is disabled, with <literal>ON</literal> it is enabled, and
with <literal>AUTO</literal> it is initially disabled, but turned on
on-the-fly once the index size reaches <xref linkend="guc-effective-cache-size"/>. The default is <literal>AUTO</literal>.
<literal>OFF</literal> buffering is disabled, with <literal>ON</literal>
it is enabled, and with <literal>AUTO</literal> it is initially disabled,
but is turned on on-the-fly once the index size reaches
<xref linkend="guc-effective-cache-size"/>. The default
is <literal>AUTO</literal>.
Note that if sorted build is possible, it will be used instead of
buffered build unless <literal>buffering=ON</literal> is specified.
</para>
</listitem>
</varlistentry>