PostgresQL FDW 源码分析之 postgresGetForeignPlan()

进入 postgresGetForeignPlan()

根据在 GetForeignRelSize() 中处理获得的 attrs_used 构造要发送到 remote 端的 SQL 语句，其中包括 targetList 和 local_conds 中提到的属性，然后加上属于 remote_conds 的 where 限制条件。

/*
* Build the query string to be sent for execution, and identify
* expressions to be sent as parameters.
*/
initStringInfo(&sql);
deparseSelectSql(&sql, root, baserel, fpinfo->attrs_used,
&retrieved_attrs);
if (remote_conds)
appendWhereClause(&sql, root, baserel, remote_conds,
true, ¶ms_list);

将构造的 SQL 语句存入 ForeignScan 结构体的 fdw_private 中，在之后的 executor 执行器时使用。

/*
* Build the fdw_private list that will be available to the executor.
* Items in the list must match enum FdwScanPrivateIndex, above.
*/
fdw_private = list_make2(makeString(sql.data),
retrieved_attrs);

/*
* Create the ForeignScan node from target list, local filtering
* expressions, remote parameter expressions, and FDW private information.
*
* Note that the remote parameter expressions are stored in the fdw_exprs
* field of the finished plan node; we can't keep them in private state
* because then they wouldn't be subject to later planner processing.
*/
return make_foreignscan(tlist,
local_exprs,
scan_relid,
params_list,
fdw_private,
NIL,	/* no custom tlist */
remote_exprs,
outer_plan);