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Add a note that regression test row ordering differences can be caused

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by non-default planner parameter settings.
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Tom Lane 2005-03-07 02:00:28 +00:00
parent 849074f9ae
commit 1fcfa038ce
1 changed files with 9 additions and 7 deletions
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doc/src/sgml/regress.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/regress.sgml,v 1.45 2004/12/28 19:08:58 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/regress.sgml,v 1.46 2005/03/07 02:00:28 tgl Exp $ -->
<chapter id="regress">
<title id="regress-title">Regression Tests</title>
@ -294,21 +294,23 @@ according to the letter of the SQL specification. In practice, since we are
looking at the same queries being executed on the same data by the same
software, we usually get the same result ordering on all platforms, and
so the lack of <literal>ORDER BY</> isn't a problem. Some queries do exhibit
cross-platform ordering differences, however. (Ordering differences
can also be triggered by non-C locale settings.)
cross-platform ordering differences, however. When testing against an
already-installed server, ordering differences can also be caused by
non-C locale settings or non-default parameter settings, such as custom values
of <varname>work_mem</> or the planner cost parameters.
</para>
<para>
Therefore, if you see an ordering difference, it's not something to
worry about, unless the query does have an <literal>ORDER BY</> that your result
is violating. But please report it anyway, so that we can add an
worry about, unless the query does have an <literal>ORDER BY</> that your
result is violating. But please report it anyway, so that we can add an
<literal>ORDER BY</> to that particular query and thereby eliminate the bogus
<quote>failure</quote> in future releases.
</para>
<para>
You might wonder why we don't order all the regression test queries explicitly to
get rid of this issue once and for all. The reason is that that would
You might wonder why we don't order all the regression test queries explicitly
to get rid of this issue once and for all. The reason is that that would
make the regression tests less useful, not more, since they'd tend
to exercise query plan types that produce ordered results to the
exclusion of those that don't.