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

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -1348,7 +1348,7 @@ SELECT t1.c1, ss.a, ss.b FROM (SELECT c1 FROM ft4 WHERE c1 between 50 and 60) t1
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Foreign Scan
Output: ft4.c1, ft4_1.c1, ft5.c1
Relations: (public.ft4) FULL JOIN ((public.ft4) FULL JOIN (public.ft5))
Relations: (public.ft4) FULL JOIN ((public.ft4 ft4_1) FULL JOIN (public.ft5))
Remote SQL: SELECT s4.c1, s10.c1, s10.c2 FROM ((SELECT c1 FROM "S 1"."T 3" WHERE ((c1 >= 50)) AND ((c1 <= 60))) s4(c1) FULL JOIN (SELECT s8.c1, s9.c1 FROM ((SELECT c1 FROM "S 1"."T 3" WHERE ((c1 >= 50)) AND ((c1 <= 60))) s8(c1) FULL JOIN (SELECT c1 FROM "S 1"."T 4" WHERE ((c1 >= 50)) AND ((c1 <= 60))) s9(c1) ON (((s8.c1 = s9.c1)))) WHERE (((s8.c1 IS NULL) OR (s8.c1 IS NOT NULL)))) s10(c1, c2) ON (((s4.c1 = s10.c1)))) ORDER BY s4.c1 ASC NULLS LAST, s10.c1 ASC NULLS LAST, s10.c2 ASC NULLS LAST
(4 rows)
@ -2084,7 +2084,7 @@ SELECT t1c1, avg(t1c1 + t2c1) FROM (SELECT t1.c1, t2.c1 FROM ft1 t1 JOIN ft2 t2
Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1"))))
-> Foreign Scan
Output: t1_1.c1, t2_1.c1
Relations: (public.ft1 t1) INNER JOIN (public.ft2 t2)
Relations: (public.ft1 t1_1) INNER JOIN (public.ft2 t2_1)
Remote SQL: SELECT r1."C 1", r2."C 1" FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1"))))
(20 rows)
@ -3230,7 +3230,7 @@ select count(*), x.b from ft1, (select c2 a, sum(c1) b from ft1 group by c2) x w
Output: x.b, x.a
-> Foreign Scan
Output: ft1_1.c2, (sum(ft1_1.c1))
Relations: Aggregate on (public.ft1)
Relations: Aggregate on (public.ft1 ft1_1)
Remote SQL: SELECT c2, sum("C 1") FROM "S 1"."T 1" GROUP BY 1
(21 rows)
@ -8480,15 +8480,15 @@ ANALYZE fprt2_p2;
-- inner join three tables
EXPLAIN (COSTS OFF)
SELECT t1.a,t2.b,t3.c FROM fprt1 t1 INNER JOIN fprt2 t2 ON (t1.a = t2.b) INNER JOIN fprt1 t3 ON (t2.b = t3.a) WHERE t1.a % 25 =0 ORDER BY 1,2,3;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------
Sort
Sort Key: t1.a, t3.c
-> Append
-> Foreign Scan
Relations: ((public.ftprt1_p1 t1) INNER JOIN (public.ftprt2_p1 t2)) INNER JOIN (public.ftprt1_p1 t3)
-> Foreign Scan
Relations: ((public.ftprt1_p2 t1) INNER JOIN (public.ftprt2_p2 t2)) INNER JOIN (public.ftprt1_p2 t3)
Relations: ((public.ftprt1_p2 t1_1) INNER JOIN (public.ftprt2_p2 t2_1)) INNER JOIN (public.ftprt1_p2 t3_1)
(7 rows)
SELECT t1.a,t2.b,t3.c FROM fprt1 t1 INNER JOIN fprt2 t2 ON (t1.a = t2.b) INNER JOIN fprt1 t3 ON (t2.b = t3.a) WHERE t1.a % 25 =0 ORDER BY 1,2,3;
@ -8507,7 +8507,7 @@ SELECT t1.a,t2.b,t2.c FROM fprt1 t1 LEFT JOIN (SELECT * FROM fprt2 WHERE a < 10)
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Foreign Scan
Output: t1.a, ftprt2_p1.b, ftprt2_p1.c
Relations: (public.ftprt1_p1 t1) LEFT JOIN (public.ftprt2_p1 fprt2)
Relations: (public.ftprt1_p1 t1) LEFT JOIN (public.ftprt2_p1)
Remote SQL: SELECT r5.a, r6.b, r6.c FROM (public.fprt1_p1 r5 LEFT JOIN public.fprt2_p1 r6 ON (((r5.a = r6.b)) AND ((r5.b = r6.a)) AND ((r6.a < 10)))) WHERE ((r5.a < 10)) ORDER BY r5.a ASC NULLS LAST, r6.b ASC NULLS LAST, r6.c ASC NULLS LAST
(4 rows)
@ -8561,15 +8561,15 @@ SELECT t1.wr, t2.wr FROM (SELECT t1 wr, a FROM fprt1 t1 WHERE t1.a % 25 = 0) t1
-- join with lateral reference
EXPLAIN (COSTS OFF)
SELECT t1.a,t1.b FROM fprt1 t1, LATERAL (SELECT t2.a, t2.b FROM fprt2 t2 WHERE t1.a = t2.b AND t1.b = t2.a) q WHERE t1.a%25 = 0 ORDER BY 1,2;
QUERY PLAN
---------------------------------------------------------------------------------
QUERY PLAN
-------------------------------------------------------------------------------------
Sort
Sort Key: t1.a, t1.b
-> Append
-> Foreign Scan
Relations: (public.ftprt1_p1 t1) INNER JOIN (public.ftprt2_p1 t2)
-> Foreign Scan
Relations: (public.ftprt1_p2 t1) INNER JOIN (public.ftprt2_p2 t2)
Relations: (public.ftprt1_p2 t1_1) INNER JOIN (public.ftprt2_p2 t2_1)
(7 rows)
SELECT t1.a,t1.b FROM fprt1 t1, LATERAL (SELECT t2.a, t2.b FROM fprt2 t2 WHERE t1.a = t2.b AND t1.b = t2.a) q WHERE t1.a%25 = 0 ORDER BY 1,2;
@ -8689,17 +8689,17 @@ SELECT a, sum(b), min(b), count(*) FROM pagg_tab GROUP BY a HAVING avg(b) < 22 O
SET enable_partitionwise_aggregate TO true;
EXPLAIN (COSTS OFF)
SELECT a, sum(b), min(b), count(*) FROM pagg_tab GROUP BY a HAVING avg(b) < 22 ORDER BY 1;
QUERY PLAN
----------------------------------------------------------------------
QUERY PLAN
-------------------------------------------------------------
Sort
Sort Key: fpagg_tab_p1.a
-> Append
-> Foreign Scan
Relations: Aggregate on (public.fpagg_tab_p1 pagg_tab)
Relations: Aggregate on (public.fpagg_tab_p1)
-> Foreign Scan
Relations: Aggregate on (public.fpagg_tab_p2 pagg_tab)
Relations: Aggregate on (public.fpagg_tab_p2)
-> Foreign Scan
Relations: Aggregate on (public.fpagg_tab_p3 pagg_tab)
Relations: Aggregate on (public.fpagg_tab_p3)
(9 rows)
SELECT a, sum(b), min(b), count(*) FROM pagg_tab GROUP BY a HAVING avg(b) < 22 ORDER BY 1;

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;
}

11
contrib/postgres_fdw/postgres_fdw.h
View File

@ -87,11 +87,14 @@ typedef struct PgFdwRelationInfo
int fetch_size; /* fetch size for this remote table */
/*
* Name of the relation while EXPLAINing ForeignScan. It is used for join
* relations but is set for all relations. For join relation, the name
* indicates which foreign tables are being joined and the join type used.
* Name of the relation, for use while EXPLAINing ForeignScan. It is used
* for join and upper relations but is set for all relations. For a base
* relation, this is really just the RT index as a string; we convert that
* while producing EXPLAIN output. For join and upper relations, the name
* indicates which base foreign tables are included and the join type or
* aggregation type used.
*/
StringInfo relation_name;
char *relation_name;
/* Join information */
RelOptInfo *outerrel;