Avoid doing catalog lookups in postgres_fdw's conversion_error_callback.

As in 50371df26, this is a bad idea since the callback can't really
know what error is being thrown and thus whether or not it is safe
to attempt catalog accesses.  Rather than pushing said accesses into
the mainline code where they'd usually be a waste of cycles, we can
look at the query's rangetable instead.

This change does mean that we'll be printing query aliases (if any
were used) rather than the table or column's true name.  But that
doesn't seem like a bad thing: it's certainly a more useful definition
in self-join cases, for instance.  In any case, it seems unlikely that
any applications would be depending on this detail, so it seems safe
to change.

Patch by me.  Original complaint by Andres Freund; Bharath Rupireddy
noted the connection to conversion_error_callback.

Discussion: https://postgr.es/m/20210106020229.ne5xnuu6wlondjpe@alap3.anarazel.de

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 475e009613f6a46bfd283a10e9e499cc4fd793e9..16287aef14375e304fb2b3b13a81af62810dd562 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -4175,15 +4175,17 @@ DROP FUNCTION f_test(int);
 -- conversion error
 -- ===================================================================
 ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE int;
-SELECT * FROM ft1 WHERE c1 = 1;  -- ERROR
+SELECT * FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8) WHERE x1 = 1;  -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  column "c8" of foreign table "ft1"
-SELECT  ft1.c1,  ft2.c2, ft1.c8 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
+CONTEXT:  column "x8" of foreign table "ftx"
+SELECT ftx.x1, ft2.c2, ftx.x8 FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  column "c8" of foreign table "ft1"
-SELECT  ft1.c1,  ft2.c2, ft1 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
+CONTEXT:  column "x8" of foreign table "ftx"
+SELECT ftx.x1, ft2.c2, ftx FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
-CONTEXT:  whole-row reference to foreign table "ft1"
+CONTEXT:  whole-row reference to foreign table "ftx"
 SELECT sum(c2), array_agg(c8) FROM ft1 GROUP BY c8; -- ERROR
 ERROR:  invalid input syntax for integer: "foo"
 CONTEXT:  processing expression at position 2 in select list

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 2af934fd0e091bed863c0b091dca02e8b166708c..a52f5121ca1ade542340d1558d749ed984095272 100644 (file)
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -244,16 +244,8 @@ typedef struct PgFdwAnalyzeState
  */
 typedef struct ConversionLocation
 {
-   Relation    rel;            /* foreign table's relcache entry. */
    AttrNumber  cur_attno;      /* attribute number being processed, or 0 */
-
-   /*
-    * In case of foreign join push down, fdw_scan_tlist is used to identify
-    * the Var node corresponding to the error location and
-    * fsstate->ss.ps.state gives access to the RTEs of corresponding relation
-    * to get the relation name and attribute name.
-    */
-   ForeignScanState *fsstate;
+   ForeignScanState *fsstate;  /* plan node being processed */
 } ConversionLocation;
 
 /* Callback argument for ec_member_matches_foreign */
@@ -5026,7 +5018,6 @@ make_tuple_from_result_row(PGresult *res,
    /*
     * Set up and install callback to report where conversion error occurs.
     */
-   errpos.rel = rel;
    errpos.cur_attno = 0;
    errpos.fsstate = fsstate;
    errcallback.callback = conversion_error_callback;
@@ -5146,35 +5137,32 @@ make_tuple_from_result_row(PGresult *res,
 /*
  * Callback function which is called when error occurs during column value
  * conversion.  Print names of column and relation.
+ *
+ * Note that this function mustn't do any catalog lookups, since we are in
+ * an already-failed transaction.  Fortunately, we can get the needed info
+ * from the query's rangetable instead.
  */
 static void
 conversion_error_callback(void *arg)
 {
+   ConversionLocation *errpos = (ConversionLocation *) arg;
+   ForeignScanState *fsstate = errpos->fsstate;
+   ForeignScan *fsplan = castNode(ForeignScan, fsstate->ss.ps.plan);
+   int         varno = 0;
+   AttrNumber  colno = 0;
    const char *attname = NULL;
    const char *relname = NULL;
    bool        is_wholerow = false;
-   ConversionLocation *errpos = (ConversionLocation *) arg;
 
-   if (errpos->rel)
+   if (fsplan->scan.scanrelid > 0)
    {
        /* error occurred in a scan against a foreign table */
-       TupleDesc   tupdesc = RelationGetDescr(errpos->rel);
-
-       if (errpos->cur_attno > 0 && errpos->cur_attno <= tupdesc->natts)
-           attname = NameStr(tupdesc->attrs[errpos->cur_attno - 1]->attname);
-       else if (errpos->cur_attno == SelfItemPointerAttributeNumber)
-           attname = "ctid";
-       else if (errpos->cur_attno == ObjectIdAttributeNumber)
-           attname = "oid";
-
-       relname = RelationGetRelationName(errpos->rel);
+       varno = fsplan->scan.scanrelid;
+       colno = errpos->cur_attno;
    }
    else
    {
        /* error occurred in a scan against a foreign join */
-       ForeignScanState *fsstate = errpos->fsstate;
-       ForeignScan *fsplan = castNode(ForeignScan, fsstate->ss.ps.plan);
-       EState     *estate = fsstate->ss.ps.state;
        TargetEntry *tle;
 
        tle = list_nth_node(TargetEntry, fsplan->fdw_scan_tlist,
@@ -5182,35 +5170,42 @@ conversion_error_callback(void *arg)
 
        /*
         * Target list can have Vars and expressions.  For Vars, we can get
-        * it's relation, however for expressions we can't.  Thus for
+        * some information, however for expressions we can't.  Thus for
         * expressions, just show generic context message.
         */
        if (IsA(tle->expr, Var))
        {
-           RangeTblEntry *rte;
            Var        *var = (Var *) tle->expr;
 
-           rte = rt_fetch(var->varno, estate->es_range_table);
-
-           if (var->varattno == 0)
-               is_wholerow = true;
-           else
-               attname = get_relid_attribute_name(rte->relid, var->varattno);
-
-           relname = get_rel_name(rte->relid);
+           varno = var->varno;
+           colno = var->varattno;
        }
-       else
-           errcontext("processing expression at position %d in select list",
-                      errpos->cur_attno);
    }
 
-   if (relname)
+   if (varno > 0)
    {
-       if (is_wholerow)
-           errcontext("whole-row reference to foreign table \"%s\"", relname);
-       else if (attname)
-           errcontext("column \"%s\" of foreign table \"%s\"", attname, relname);
+       EState     *estate = fsstate->ss.ps.state;
+       RangeTblEntry *rte = rt_fetch(varno, estate->es_range_table);
+
+       relname = rte->eref->aliasname;
+
+       if (colno == 0)
+           is_wholerow = true;
+       else if (colno > 0 && colno <= list_length(rte->eref->colnames))
+           attname = strVal(list_nth(rte->eref->colnames, colno - 1));
+       else if (colno == SelfItemPointerAttributeNumber)
+           attname = "ctid";
+       else if (colno == ObjectIdAttributeNumber)
+           attname = "oid";
    }
+
+   if (relname && is_wholerow)
+       errcontext("whole-row reference to foreign table \"%s\"", relname);
+   else if (relname && attname)
+       errcontext("column \"%s\" of foreign table \"%s\"", attname, relname);
+   else
+       errcontext("processing expression at position %d in select list",
+                  errpos->cur_attno);
 }
 
 /*

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 7982117596cbc8e496fe649a7121dbf3c21b88a7..e1cef0788503be3974ec56f4d33dcf9d13054d89 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1055,9 +1055,11 @@ DROP FUNCTION f_test(int);
 -- conversion error
 -- ===================================================================
 ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE int;
-SELECT * FROM ft1 WHERE c1 = 1;  -- ERROR
-SELECT  ft1.c1,  ft2.c2, ft1.c8 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
-SELECT  ft1.c1,  ft2.c2, ft1 FROM ft1, ft2 WHERE ft1.c1 = ft2.c1 AND ft1.c1 = 1; -- ERROR
+SELECT * FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8) WHERE x1 = 1;  -- ERROR
+SELECT ftx.x1, ft2.c2, ftx.x8 FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
+SELECT ftx.x1, ft2.c2, ftx FROM ft1 ftx(x1,x2,x3,x4,x5,x6,x7,x8), ft2
+  WHERE ftx.x1 = ft2.c1 AND ftx.x1 = 1; -- ERROR
 SELECT sum(c2), array_agg(c8) FROM ft1 GROUP BY c8; -- ERROR
 ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE user_enum;