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tr class="diff-line-row"> | 1 | 1 | <!-- |
2 | | -$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.42 2004/03/09 16:57:46 neilc Exp $ |
| 2 | +$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.43 2004/03/25 18:57:57 tgl Exp $ |
3 | 3 | --> |
4 | 4 |
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5 | 5 | <chapter id="performance-tips"> |
@@ -120,7 +120,8 @@ SELECT * FROM pg_class WHERE relname = 'tenk1'; |
120 | 120 |
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121 | 121 | you will find out that <classname>tenk1</classname> has 233 disk |
122 | 122 | pages and 10000 rows. So the cost is estimated at 233 page |
123 | | - reads, defined as costing 1.0 apiece, plus 10000 * <varname>cpu_tuple_cost</varname> which is |
| 123 | + reads, defined as costing 1.0 apiece, plus 10000 * <xref |
| 124 | + linkend="guc-cpu-tuple-cost"> which is |
124 | 125 | currently 0.01 (try <command>SHOW cpu_tuple_cost</command>). |
125 | 126 | </para> |
126 | 127 |
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@@ -450,7 +451,7 @@ SELECT attname, n_distinct, most_common_vals FROM pg_stats WHERE tablename = 'ro |
450 | 451 | arrays for each column, can be set on a |
451 | 452 | column-by-column basis using the <command>ALTER TABLE SET STATISTICS</> |
452 | 453 | command, or globally by setting the |
453 | | - <varname>default_statistics_target</varname> runtime parameter. |
| 454 | + <xref linkend="guc-default-statistics-target"> configuration variable. |
454 | 455 | The default limit is presently 10 entries. Raising the limit |
455 | 456 | may allow more accurate planner estimates to be made, particularly for |
456 | 457 | 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; |
599 | 600 | problem replacing two separate three-way join problems. Because of the |
600 | 601 | exponential growth of the number of possibilities, this makes a big |
601 | 602 | difference. The planner tries to avoid getting stuck in huge join search |
602 | | - problems by not collapsing a subquery if more than <xref linkend="guc-from-collapse-limit"> |
| 603 | + problems by not collapsing a subquery if more than <varname>from_collapse_limit</> |
603 | 604 | <literal>FROM</> items would result in the parent |
604 | 605 | query. You can trade off planning time against quality of plan by |
605 | 606 | adjusting this run-time parameter up or down. |
606 | 607 | </para> |
607 | 608 |
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608 | 609 | <para> |
609 | | - <varname>from_collapse_limit</> and <varname>join_collapse_limit</> |
| 610 | + <xref linkend="guc-from-collapse-limit"> and <xref |
| 611 | + linkend="guc-join-collapse-limit"> |
610 | 612 | are similarly named because they do almost the same thing: one controls |
611 | 613 | when the planner will <quote>flatten out</> subselects, and the |
612 | 614 | other controls when it will flatten out explicit inner joins. Typically |
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