diff options
Diffstat (limited to 'doc/src/sgml/indexam.sgml')
| -rw-r--r-- | doc/src/sgml/indexam.sgml | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml index a6e4466e8a..ebd32cc8d9 100644 --- a/doc/src/sgml/indexam.sgml +++ b/doc/src/sgml/indexam.sgml @@ -134,11 +134,6 @@ <structfield>amsearchnulls</structfield>, indicating that it supports <literal>IS NULL</> and <literal>IS NOT NULL</> clauses as search conditions. - An index method can also set <structfield>amcanreturn</structfield>, - indicating that it can support <firstterm>index-only scans</> by returning - the indexed column values for an index entry in the form of an IndexTuple. - (An example of an index AM that cannot do this is hash, which stores only - the hash values not the original data.) </para> </sect1> @@ -278,6 +273,19 @@ amvacuumcleanup (IndexVacuumInfo *info, <para> <programlisting> +bool +amcanreturn (Relation indexRelation); +</programlisting> + Check whether the index can support <firstterm>index-only scans</> by + returning the indexed column values for an index entry in the form of an + IndexTuple. Return TRUE if so, else FALSE. If the index AM can never + support index-only scans (an example is hash, which stores only + the hash values not the original data), it is sufficient to set its + <structfield>amcanreturn</> field to zero in <structname>pg_am</>. + </para> + + <para> +<programlisting> void amcostestimate (PlannerInfo *root, IndexOptInfo *index, @@ -391,9 +399,9 @@ amgettuple (IndexScanDesc scan, </para> <para> - If the access method supports index-only scans (i.e., - <structfield>amcanreturn</structfield> is TRUE in its <structname>pg_am</> - row), then on success it must also check + If the index supports index-only scans (i.e., + <function>amcanreturn</function> returns TRUE for it), + then on success the AM must also check <literal>scan->xs_want_itup</>, and if that is true it must return the original indexed data for the index entry, in the form of an <structname>IndexTuple</> pointer stored at <literal>scan->xs_itup</>, |