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Disable support for partitionwise joins in problematic cases.

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Commit f49842d, which added support for partitionwise joins, built the
child's tlist by applying adjust_appendrel_attrs() to the parent's.  So in
the case where the parent's included a whole-row Var for the parent, the
child's contained a ConvertRowtypeExpr.  To cope with that, that commit
added code to the planner, such as setrefs.c, but some code paths still
assumed that the tlist for a scan (or join) rel would only include Vars
and PlaceHolderVars, which was true before that commit, causing errors:

* When creating an explicit sort node for an input path for a mergejoin
  path for a child join, prepare_sort_from_pathkeys() threw the 'could not
  find pathkey item to sort' error.
* When deparsing a relation participating in a pushed down child join as a
  subquery in contrib/postgres_fdw, get_relation_column_alias_ids() threw
  the 'unexpected expression in subquery output' error.
* When performing set_plan_references() on a local join plan generated by
  contrib/postgres_fdw for EvalPlanQual support for a pushed down child
  join, fix_join_expr() threw the 'variable not found in subplan target
  lists' error.

To fix these, two approaches have been proposed: one by Ashutosh Bapat and
one by me.  While the former keeps building the child's tlist with a
ConvertRowtypeExpr, the latter builds it with a whole-row Var for the
child not to violate the planner assumption, and tries to fix it up later,
But both approaches need more work, so refuse to generate partitionwise
join paths when whole-row Vars are involved, instead.  We don't need to
handle ConvertRowtypeExprs in the child's tlists for now, so this commit
also removes the changes to the planner.

Previously, partitionwise join computed attr_needed data for each child
separately, and built the child join's tlist using that data, which also
required an extra step for adding PlaceHolderVars to that tlist, but it
would be more efficient to build it from the parent join's tlist through
the adjust_appendrel_attrs() transformation.  So this commit builds that
list that way, and simplifies build_joinrel_tlist() and placeholder.c as
well as part of set_append_rel_size() to basically what they were before
partitionwise join went in.

Back-patch to PG11 where partitionwise join was introduced.

Report by Rajkumar Raghuwanshi.  Analysis by Ashutosh Bapat, who also
provided some of regression tests.  Patch by me, reviewed by Robert Haas.

Discussion: https://postgr.es/m/CAKcux6ktu-8tefLWtQuuZBYFaZA83vUzuRd7c1YHC-yEWyYFpg@mail.gmail.com
This commit is contained in:
Etsuro Fujita
2018-08-31 20:47:17 +09:00
parent 762a16572b
commit 940487956e
13 changed files with 266 additions and 256 deletions
Download Patch File Download Diff File Expand all files Collapse all files

78
src/backend/optimizer/path/allpaths.c
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@ -909,6 +909,17 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
did_pruning = true;
}
/*
* If this is a partitioned baserel, set the consider_partitionwise_join
* flag; currently, we only consider partitionwise joins with the baserel
* if its targetlist doesn't contain a whole-row Var.
*/
if (enable_partitionwise_join &&
rel->reloptkind == RELOPT_BASEREL &&
rte->relkind == RELKIND_PARTITIONED_TABLE &&
rel->attr_needed[InvalidAttrNumber - rel->min_attr] == NULL)
rel->consider_partitionwise_join = true;
/*
* Initialize to compute size estimates for whole append relation.
*
@ -956,54 +967,6 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
childrel = find_base_rel(root, childRTindex);
Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL);
if (rel->part_scheme)
{
AttrNumber attno;
/*
* We need attr_needed data for building targetlist of a join
* relation representing join between matching partitions for
* partitionwise join. A given attribute of a child will be needed
* in the same highest joinrel where the corresponding attribute
* of parent is needed. Hence it suffices to use the same Relids
* set for parent and child.
*/
for (attno = rel->min_attr; attno <= rel->max_attr; attno++)
{
int index = attno - rel->min_attr;
Relids attr_needed = rel->attr_needed[index];
/* System attributes do not need translation. */
if (attno <= 0)
{
Assert(rel->min_attr == childrel->min_attr);
childrel->attr_needed[index] = attr_needed;
}
else
{
Var *var = list_nth_node(Var,
appinfo->translated_vars,
attno - 1);
int child_index;
/*
* Ignore any column dropped from the parent.
* Corresponding Var won't have any translation. It won't
* have attr_needed information, since it can not be
* referenced in the query.
*/
if (var == NULL)
{
Assert(attr_needed == NULL);
continue;
}
child_index = var->varattno - childrel->min_attr;
childrel->attr_needed[child_index] = attr_needed;
}
}
}
/*
* Copy/Modify targetlist. Even if this child is deemed empty, we need
* its targetlist in case it falls on nullable side in a child-join
@ -1180,6 +1143,22 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
(Node *) rel->joininfo,
1, &appinfo);
/*
* Note: we could compute appropriate attr_needed data for the child's
* variables, by transforming the parent's attr_needed through the
* translated_vars mapping. However, currently there's no need
* because attr_needed is only examined for base relations not
* otherrels. So we just leave the child's attr_needed empty.
*/
/*
* If we consider partitionwise joins with the parent rel, do the same
* for partitioned child rels.
*/
if (rel->consider_partitionwise_join &&
childRTE->relkind == RELKIND_PARTITIONED_TABLE)
childrel->consider_partitionwise_join = true;
/*
* If parallelism is allowable for this query in general, see whether
* it's allowable for this childrel in particular. But if we've
@ -3538,6 +3517,9 @@ generate_partitionwise_join_paths(PlannerInfo *root, RelOptInfo *rel)
if (!IS_PARTITIONED_REL(rel))
return;
/* The relation should have consider_partitionwise_join set. */
Assert(rel->consider_partitionwise_join);
/* Guard against stack overflow due to overly deep partition hierarchy. */
check_stack_depth();