PostgreSQL在何处处理 sql查询之二十五

再次梳理 build_simple_rel 的执行内容：

/*
* build_simple_rel
*      Construct a new RelOptInfo for a base relation or 'other' relation.
*/
RelOptInfo *
build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
{
RelOptInfo *rel;
RangeTblEntry *rte;

/* Rel should not exist already */
Assert(relid > 0 && relid < root->simple_rel_array_size);
if (root->simple_rel_array[relid] != NULL)
elog(ERROR, "rel %d already exists", relid);

/* Fetch RTE for relation */
rte = root->simple_rte_array[relid];
Assert(rte != NULL);

rel = makeNode(RelOptInfo);
rel->reloptkind = reloptkind;
rel->relids = bms_make_singleton(relid);
rel->rows = 0;
...
rel->has_eclass_joins = false;

/* Check type of rtable entry */
switch (rte->rtekind)
{
case RTE_RELATION:
/* Table --- retrieve statistics from the system catalogs */
get_relation_info(root, rte->relid, rte->inh, rel);
break;
case RTE_SUBQUERY:
case RTE_FUNCTION:
case RTE_VALUES:
case RTE_CTE:

/*
* Subquery, function, or values list --- set up attr range and
* arrays
*
* Note: 0 is included in range to support whole-row Vars
*/
rel->min_attr = 0;
rel->max_attr = list_length(rte->eref->colnames);
rel->attr_needed = (Relids *)
palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(Relids));
rel->attr_widths = (int32 *)
palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(int32));
break;
default:
elog(ERROR, "unrecognized RTE kind: %d",
(int) rte->rtekind);
break;
}

/* Save the finished struct in the query's simple_rel_array */
root->simple_rel_array[relid] = rel;

...
return rel;
}

可以看出，这是准备了 表信息的结构--RelOptInfo，然后再把它挂在计划树上：

root->simple_rel_array[relid] = rel;

需要注意的是，这里 relid 是 simple_rel_array数组的下标，而非oid。