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postgres_fdw: Perform the (ORDERED, NULL) upperrel operations remotely.

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The upper-planner pathification allows FDWs to arrange to push down
different types of upper-stage operations to the remote side.  This
commit teaches postgres_fdw to do it for the (ORDERED, NULL) upperrel,
which is responsible for evaluating the query's ORDER BY ordering.
Since postgres_fdw is already able to evaluate that ordering remotely
for foreign baserels and foreign joinrels (see commit aa09cd242f et al.),
this adds support for that for foreign grouping relations.

Author: Etsuro Fujita
Reviewed-By: Antonin Houska and Jeff Janes
Discussion: https://postgr.es/m/87pnz1aby9.fsf@news-spur.riddles.org.uk
This commit is contained in:
Etsuro Fujita
2019-04-02 19:20:30 +09:00
parent e2d28c0f40
commit ffab494a4d
4 changed files with 457 additions and 138 deletions
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28
contrib/postgres_fdw/deparse.c
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@ -167,7 +167,8 @@ static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
static void deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
deparse_expr_cxt *context);
static void deparseLockingClause(deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, bool has_final_sort,
deparse_expr_cxt *context);
static void appendConditions(List *exprs, deparse_expr_cxt *context);
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
RelOptInfo *foreignrel, bool use_alias,
@ -929,8 +930,8 @@ build_tlist_to_deparse(RelOptInfo *foreignrel)
void
deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
List *tlist, List *remote_conds, List *pathkeys,
bool is_subquery, List **retrieved_attrs,
List **params_list)
bool has_final_sort, bool is_subquery,
List **retrieved_attrs, List **params_list)
{
deparse_expr_cxt context;
PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
@ -985,7 +986,7 @@ deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
/* Add ORDER BY clause if we found any useful pathkeys */
if (pathkeys)
appendOrderByClause(pathkeys, &context);
appendOrderByClause(pathkeys, has_final_sort, &context);
/* Add any necessary FOR UPDATE/SHARE. */
deparseLockingClause(&context);
@ -1590,7 +1591,7 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
/* Deparse the subquery representing the relation. */
appendStringInfoChar(buf, '(');
deparseSelectStmtForRel(buf, root, foreignrel, NIL,
fpinfo->remote_conds, NIL, true,
fpinfo->remote_conds, NIL, false, true,
&retrieved_attrs, params_list);
appendStringInfoChar(buf, ')');
@ -3109,7 +3110,8 @@ appendGroupByClause(List *tlist, deparse_expr_cxt *context)
* base relation are obtained and deparsed.
*/
static void
appendOrderByClause(List *pathkeys, deparse_expr_cxt *context)
appendOrderByClause(List *pathkeys, bool has_final_sort,
deparse_expr_cxt *context)
{
ListCell *lcell;
int nestlevel;
@ -3126,7 +3128,19 @@ appendOrderByClause(List *pathkeys, deparse_expr_cxt *context)
PathKey *pathkey = lfirst(lcell);
Expr *em_expr;
em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
if (has_final_sort)
{
/*
* By construction, context->foreignrel is the input relation to
* the final sort.
*/
em_expr = find_em_expr_for_input_target(context->root,
pathkey->pk_eclass,
context->foreignrel->reltarget);
}
else
em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
Assert(em_expr != NULL);
appendStringInfoString(buf, delim);