diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/indexam.sgml | 25 |
1 files changed, 12 insertions, 13 deletions
diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml index 07c816c38f2..28f2ae16275 100644 --- a/doc/src/sgml/indexam.sgml +++ b/doc/src/sgml/indexam.sgml @@ -289,7 +289,7 @@ amcanreturn (Relation indexRelation); void amcostestimate (PlannerInfo *root, IndexPath *path, - RelOptInfo *outer_rel, + double loop_count, Cost *indexStartupCost, Cost *indexTotalCost, Selectivity *indexSelectivity, @@ -928,7 +928,7 @@ amrestrpos (IndexScanDesc scan); void amcostestimate (PlannerInfo *root, IndexPath *path, - RelOptInfo *outer_rel, + double loop_count, Cost *indexStartupCost, Cost *indexTotalCost, Selectivity *indexSelectivity, @@ -958,16 +958,15 @@ amcostestimate (PlannerInfo *root, </varlistentry> <varlistentry> - <term><parameter>outer_rel</></term> + <term><parameter>loop_count</></term> <listitem> <para> - If the index is being considered for use in a join inner indexscan, - the planner's information about the outer side of the join. Otherwise - <symbol>NULL</>. When non-<symbol>NULL</>, some of the qual clauses - will be join clauses for joins - with this rel rather than being simple restriction clauses. Also, - the cost estimator should expect that the index scan will be repeated - for each row of the outer rel. + The number of repetitions of the index scan that should be factored + into the cost estimates. This will typically be greater than one when + considering a parameterized scan for use in the inside of a nestloop + join. Note that the cost estimates should still be for just one scan; + a larger <parameter>loop_count</> means that it may be appropriate + to allow for some caching effects across multiple scans. </para> </listitem> </varlistentry> @@ -1062,8 +1061,8 @@ amcostestimate (PlannerInfo *root, </para> <para> - In the join case, the returned numbers should be averages expected for - any one scan of the index. + When <parameter>loop_count</> is greater than one, the returned numbers + should be averages expected for any one scan of the index. </para> <procedure> @@ -1121,7 +1120,7 @@ cost_qual_eval(&index_qual_cost, path->indexquals, root); </programlisting> However, the above does not account for amortization of index reads - across repeated index scans in the join case. + across repeated index scans. </para> </step> |