diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/fdwhandler.sgml | 33 |
1 files changed, 21 insertions, 12 deletions
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml index 76ff243f5d3..12c5f75bfab 100644 --- a/doc/src/sgml/fdwhandler.sgml +++ b/doc/src/sgml/fdwhandler.sgml @@ -88,21 +88,31 @@ <para> <programlisting> -FdwPlan * +void PlanForeignScan (Oid foreigntableid, PlannerInfo *root, RelOptInfo *baserel); </programlisting> - Plan a scan on a foreign table. This is called when a query is planned. + Create possible access paths for a scan on a foreign table. This is + called when a query is planned. <literal>foreigntableid</> is the <structname>pg_class</> OID of the foreign table. <literal>root</> is the planner's global information about the query, and <literal>baserel</> is the planner's information about this table. - The function must return a palloc'd struct that contains cost estimates - plus any FDW-private information that is needed to execute the foreign - scan at a later time. (Note that the private information must be - represented in a form that <function>copyObject</> knows how to copy.) + </para> + + <para> + The function must generate at least one access path (ForeignPath node) + for a scan on the foreign table and must call <function>add_path</> to + add the path to <literal>baserel->pathlist</>. It's recommended to + use <function>create_foreignscan_path</> to build the ForeignPath node. + The function may generate multiple access paths, e.g., a path which has + valid <literal>pathkeys</> to represent a pre-sorted result. Each access + path must contain cost estimates, and can contain any FDW-private + information that is needed to execute the foreign scan at a later time. + (Note that the private information must be represented in a form that + <function>copyObject</> knows how to copy.) </para> <para> @@ -159,9 +169,8 @@ BeginForeignScan (ForeignScanState *node, its <structfield>fdw_state</> field is still NULL. Information about the table to scan is accessible through the <structname>ForeignScanState</> node (in particular, from the underlying - <structname>ForeignScan</> plan node, which contains a pointer to the - <structname>FdwPlan</> structure returned by - <function>PlanForeignScan</>). + <structname>ForeignScan</> plan node, which contains any FDW-private + information provided by <function>PlanForeignScan</>). </para> <para> @@ -228,9 +237,9 @@ EndForeignScan (ForeignScanState *node); </para> <para> - The <structname>FdwRoutine</> and <structname>FdwPlan</> struct types - are declared in <filename>src/include/foreign/fdwapi.h</>, which see - for additional details. + The <structname>FdwRoutine</> struct type is declared in + <filename>src/include/foreign/fdwapi.h</>, which see for additional + details. </para> </sect1> |