diff options
Diffstat (limited to 'doc/src/sgml/indexam.sgml')
| -rw-r--r-- | doc/src/sgml/indexam.sgml | 28 |
1 files changed, 14 insertions, 14 deletions
diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml index 70fba4ecc0a..4bf14ba7e60 100644 --- a/doc/src/sgml/indexam.sgml +++ b/doc/src/sgml/indexam.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.12 2006/05/24 11:01:39 teodor Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.13 2006/06/05 02:49:58 tgl Exp $ --> <chapter id="indexam"> <title>Index Access Method Interface Definition</title> @@ -771,14 +771,14 @@ amcostestimate (PlannerInfo *root, </para> <para> - The index access costs should be computed in the units used by + The index access costs should be computed using the parameters used by <filename>src/backend/optimizer/path/costsize.c</filename>: a sequential - disk block fetch has cost 1.0, a nonsequential fetch has cost - <varname>random_page_cost</>, and the cost of processing one index row - should usually be taken as <varname>cpu_index_tuple_cost</>. In addition, - an appropriate multiple of <varname>cpu_operator_cost</> should be charged - for any comparison operators invoked during index processing (especially - evaluation of the indexQuals themselves). + disk block fetch has cost <varname>seq_page_cost</>, a nonsequential fetch + has cost <varname>random_page_cost</>, and the cost of processing one index + row should usually be taken as <varname>cpu_index_tuple_cost</>. In + addition, an appropriate multiple of <varname>cpu_operator_cost</> should + be charged for any comparison operators invoked during index processing + (especially evaluation of the indexQuals themselves). </para> <para> @@ -788,10 +788,10 @@ amcostestimate (PlannerInfo *root, </para> <para> - The <quote>start-up cost</quote> is the part of the total scan cost that must be expended - before we can begin to fetch the first row. For most indexes this can - be taken as zero, but an index type with a high start-up cost might want - to set it nonzero. + The <quote>start-up cost</quote> is the part of the total scan cost that + must be expended before we can begin to fetch the first row. For most + indexes this can be taken as zero, but an index type with a high start-up + cost might want to set it nonzero. </para> <para> @@ -850,13 +850,13 @@ amcostestimate (PlannerInfo *root, <programlisting> /* * Our generic assumption is that the index pages will be read - * sequentially, so they have cost 1.0 each, not random_page_cost. + * sequentially, so they cost seq_page_cost each, not random_page_cost. * Also, we charge for evaluation of the indexquals at each index row. * All the costs are assumed to be paid incrementally during the scan. */ cost_qual_eval(&index_qual_cost, indexQuals); *indexStartupCost = index_qual_cost.startup; - *indexTotalCost = numIndexPages + + *indexTotalCost = seq_page_cost * numIndexPages + (cpu_index_tuple_cost + index_qual_cost.per_tuple) * numIndexTuples; </programlisting> </para> |