From 7a944e41b4fc47a9e11d38a90829fac0f81e30b0 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 25 Mar 2004 18:57:57 +0000 Subject: [PATCH] Convert some GUC variable references to links. --- doc/src/sgml/perform.sgml | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index b32b1d615d..f8b1d47aa9 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1,5 +1,5 @@ @@ -120,7 +120,8 @@ SELECT * FROM pg_class WHERE relname = 'tenk1'; you will find out that tenk1 has 233 disk pages and 10000 rows. So the cost is estimated at 233 page - reads, defined as costing 1.0 apiece, plus 10000 * cpu_tuple_cost which is + reads, defined as costing 1.0 apiece, plus 10000 * which is currently 0.01 (try SHOW cpu_tuple_cost). @@ -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 ALTER TABLE SET STATISTICS command, or globally by setting the - default_statistics_target runtime parameter. + 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 + problems by not collapsing a subquery if more than from_collapse_limit 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. - from_collapse_limit and join_collapse_limit + and are similarly named because they do almost the same thing: one controls when the planner will flatten out subselects, and the other controls when it will flatten out explicit inner joins. Typically -- 2.11.0