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Make postgres_fdw's "Relations" output agree with the rest of EXPLAIN.

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The relation aliases shown in the "Relations" line for a foreign scan
didn't always agree with those used in the rest of EXPLAIN's output.
The regression test result changes appearing here provide examples.

It's really impossible for postgres_fdw to duplicate EXPLAIN's alias
assignment logic during postgresGetForeignRelSize(), because of the
de-duplication that EXPLAIN does on a global basis --- and anyway,
trying to duplicate that would be unmaintainable.  Instead, just put
numeric rangetable indexes into the string, and convert those to
table names/aliases in postgresExplainForeignScan, which does have
access to the results of ruleutils.c's alias assignment logic.
Aside from being more reliable, this shifts some work from planning
to EXPLAIN, which is a good tradeoff for performance.  (I also
changed from using StringInfo to using psprintf, which makes the
code slightly simpler and reduces its memory consumption.)

A kluge required by this solution is that we have to reverse-engineer
the rtoffset applied by setrefs.c.  If that logic ever fails
(presumably because the member tables of a join got offset by
different amounts), we'll need some more cooperation with setrefs.c
to keep things straight.  But for now, there's no need for that.

Arguably this is a back-patchable bug fix, but since this is a mostly
cosmetic issue and there have been no field complaints, I'll refrain
for now.

Discussion: https://postgr.es/m/12424.1575168015@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-12-02 16:31:03 -05:00
parent 1d468b9ad8
commit 4526951d56
3 changed files with 117 additions and 56 deletions
Download Patch File Download Diff File Expand all files Collapse all files

132
contrib/postgres_fdw/postgres_fdw.c
View File

@ -12,6 +12,8 @@
*/
#include "postgres.h"
#include <limits.h>
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/table.h"
@ -574,9 +576,6 @@ postgresGetForeignRelSize(PlannerInfo *root,
PgFdwRelationInfo *fpinfo;
ListCell *lc;
RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
const char *namespace;
const char *relname;
const char *refname;
/*
* We use PgFdwRelationInfo to pass various information to subsequent
@ -719,21 +718,11 @@ postgresGetForeignRelSize(PlannerInfo *root,
}
/*
* Set the name of relation in fpinfo, while we are constructing it here.
* It will be used to build the string describing the join relation in
* EXPLAIN output. We can't know whether VERBOSE option is specified or
* not, so always schema-qualify the foreign table name.
* fpinfo->relation_name gets the numeric rangetable index of the foreign
* table RTE. (If this query gets EXPLAIN'd, we'll convert that to a
* human-readable string at that time.)
*/
fpinfo->relation_name = makeStringInfo();
namespace = get_namespace_name(get_rel_namespace(foreigntableid));
relname = get_rel_name(foreigntableid);
refname = rte->eref->aliasname;
appendStringInfo(fpinfo->relation_name, "%s.%s",
quote_identifier(namespace),
quote_identifier(relname));
if (*refname && strcmp(refname, relname) != 0)
appendStringInfo(fpinfo->relation_name, " %s",
quote_identifier(rte->eref->aliasname));
fpinfo->relation_name = psprintf("%u", baserel->relid);
/* No outer and inner relations. */
fpinfo->make_outerrel_subquery = false;
@ -1376,7 +1365,7 @@ postgresGetForeignPlan(PlannerInfo *root,
makeInteger(fpinfo->fetch_size));
if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
fdw_private = lappend(fdw_private,
makeString(fpinfo->relation_name->data));
makeString(fpinfo->relation_name));
/*
* Create the ForeignScan node for the given relation.
@ -2528,20 +2517,85 @@ postgresEndDirectModify(ForeignScanState *node)
static void
postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
{
List *fdw_private;
char *sql;
char *relations;
fdw_private = ((ForeignScan *) node->ss.ps.plan)->fdw_private;
ForeignScan *plan = castNode(ForeignScan, node->ss.ps.plan);
List *fdw_private = plan->fdw_private;
/*
* Add names of relation handled by the foreign scan when the scan is a
* join
* Identify foreign scans that are really joins or upper relations. The
* input looks something like "(1) LEFT JOIN (2)", and we must replace the
* digit string(s), which are RT indexes, with the correct relation names.
* We do that here, not when the plan is created, because we can't know
* what aliases ruleutils.c will assign at plan creation time.
*/
if (list_length(fdw_private) > FdwScanPrivateRelations)
{
relations = strVal(list_nth(fdw_private, FdwScanPrivateRelations));
ExplainPropertyText("Relations", relations, es);
StringInfo relations;
char *rawrelations;
char *ptr;
int minrti,
rtoffset;
rawrelations = strVal(list_nth(fdw_private, FdwScanPrivateRelations));
/*
* A difficulty with using a string representation of RT indexes is
* that setrefs.c won't update the string when flattening the
* rangetable. To find out what rtoffset was applied, identify the
* minimum RT index appearing in the string and compare it to the
* minimum member of plan->fs_relids. (We expect all the relids in
* the join will have been offset by the same amount; the Asserts
* below should catch it if that ever changes.)
*/
minrti = INT_MAX;
ptr = rawrelations;
while (*ptr)
{
if (isdigit((unsigned char) *ptr))
{
int rti = strtol(ptr, &ptr, 10);
if (rti < minrti)
minrti = rti;
}
else
ptr++;
}
rtoffset = bms_next_member(plan->fs_relids, -1) - minrti;
/* Now we can translate the string */
relations = makeStringInfo();
ptr = rawrelations;
while (*ptr)
{
if (isdigit((unsigned char) *ptr))
{
int rti = strtol(ptr, &ptr, 10);
RangeTblEntry *rte;
char *namespace;
char *relname;
char *refname;
rti += rtoffset;
Assert(bms_is_member(rti, plan->fs_relids));
rte = rt_fetch(rti, es->rtable);
Assert(rte->rtekind == RTE_RELATION);
/* This logic should agree with explain.c's ExplainTargetRel */
namespace = get_namespace_name(get_rel_namespace(rte->relid));
relname = get_rel_name(rte->relid);
appendStringInfo(relations, "%s.%s",
quote_identifier(namespace),
quote_identifier(relname));
refname = (char *) list_nth(es->rtable_names, rti - 1);
if (refname == NULL)
refname = rte->eref->aliasname;
if (strcmp(refname, relname) != 0)
appendStringInfo(relations, " %s",
quote_identifier(refname));
}
else
appendStringInfoChar(relations, *ptr++);
}
ExplainPropertyText("Relations", relations->data, es);
}
/*
@ -2549,6 +2603,8 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
*/
if (es->verbose)
{
char *sql;
sql = strVal(list_nth(fdw_private, FdwScanPrivateSelectSql));
ExplainPropertyText("Remote SQL", sql, es);
}
@ -5171,13 +5227,14 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
/*
* Set the string describing this join relation to be used in EXPLAIN
* output of corresponding ForeignScan.
* output of corresponding ForeignScan. Note that the decoration we add
* to the base relation names mustn't include any digits, or it'll confuse
* postgresExplainForeignScan.
*/
fpinfo->relation_name = makeStringInfo();
appendStringInfo(fpinfo->relation_name, "(%s) %s JOIN (%s)",
fpinfo_o->relation_name->data,
get_jointype_name(fpinfo->jointype),
fpinfo_i->relation_name->data);
fpinfo->relation_name = psprintf("(%s) %s JOIN (%s)",
fpinfo_o->relation_name,
get_jointype_name(fpinfo->jointype),
fpinfo_i->relation_name);
/*
* Set the relation index. This is defined as the position of this
@ -5723,11 +5780,12 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
/*
* Set the string describing this grouped relation to be used in EXPLAIN
* output of corresponding ForeignScan.
* output of corresponding ForeignScan. Note that the decoration we add
* to the base relation name mustn't include any digits, or it'll confuse
* postgresExplainForeignScan.
*/
fpinfo->relation_name = makeStringInfo();
appendStringInfo(fpinfo->relation_name, "Aggregate on (%s)",
ofpinfo->relation_name->data);
fpinfo->relation_name = psprintf("Aggregate on (%s)",
ofpinfo->relation_name);
return true;
}