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author | Tom Lane <tgl@sss.pgh.pa.us> | 2004-03-25 18:57:57 +0000 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2004-03-25 18:57:57 +0000 |
commit | 7a944e41b4fc47a9e11d38a90829fac0f81e30b0 (patch) | |
tree | c4bbe7457ebda9bb3a453322f5dbdf723ee78294 | |
parent | eebdfcdbe6e3ee7432229ac51e37d9a422836fda (diff) | |
download | postgresql-7a944e41b4fc47a9e11d38a90829fac0f81e30b0.tar.gz postgresql-7a944e41b4fc47a9e11d38a90829fac0f81e30b0.zip |
Convert some GUC variable references to links.
-rw-r--r-- | doc/src/sgml/perform.sgml | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index b32b1d615d1..f8b1d47aa9e 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.42 2004/03/09 16:57:46 neilc Exp $ +$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.43 2004/03/25 18:57:57 tgl Exp $ --> <chapter id="performance-tips"> @@ -120,7 +120,8 @@ SELECT * FROM pg_class WHERE relname = 'tenk1'; you will find out that <classname>tenk1</classname> has 233 disk pages and 10000 rows. So the cost is estimated at 233 page - reads, defined as costing 1.0 apiece, plus 10000 * <varname>cpu_tuple_cost</varname> which is + reads, defined as costing 1.0 apiece, plus 10000 * <xref + linkend="guc-cpu-tuple-cost"> which is currently 0.01 (try <command>SHOW cpu_tuple_cost</command>). </para> @@ -450,7 +451,7 @@ SELECT attname, n_distinct, most_common_vals FROM pg_stats WHERE tablename = 'ro arrays for each column, can be set on a column-by-column basis using the <command>ALTER TABLE SET STATISTICS</> command, or globally by setting the - <varname>default_statistics_target</varname> runtime parameter. + <xref linkend="guc-default-statistics-target"> configuration variable. The default limit is presently 10 entries. Raising the limit may allow more accurate planner estimates to be made, particularly for columns with irregular data distributions, at the price of consuming @@ -599,14 +600,15 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse; problem replacing two separate three-way join problems. Because of the exponential growth of the number of possibilities, this makes a big difference. The planner tries to avoid getting stuck in huge join search - problems by not collapsing a subquery if more than <xref linkend="guc-from-collapse-limit"> + problems by not collapsing a subquery if more than <varname>from_collapse_limit</> <literal>FROM</> items would result in the parent query. You can trade off planning time against quality of plan by adjusting this run-time parameter up or down. </para> <para> - <varname>from_collapse_limit</> and <varname>join_collapse_limit</> + <xref linkend="guc-from-collapse-limit"> and <xref + linkend="guc-join-collapse-limit"> are similarly named because they do almost the same thing: one controls when the planner will <quote>flatten out</> subselects, and the other controls when it will flatten out explicit inner joins. Typically |