Improve unique-constraint-violation error messages to include the exact

values being complained of.

In passing, also remove the arbitrary length limitation in the similar
error detail message for foreign key violations.

Itagaki Takahiro

src/backend/access/common/indextuple.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/common/indextuple.c,v 1.88 2009/06/11 14:48:53 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/common/indextuple.c,v 1.89 2009/08/01 19:59:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -432,6 +432,27 @@ nocache_index_getattr(IndexTuple tup,
 	return fetchatt(att[attnum], tp + off);
 }
 
+/*
+ * Convert an index tuple into Datum/isnull arrays.
+ *
+ * The caller must allocate sufficient storage for the output arrays.
+ * (INDEX_MAX_KEYS entries should be enough.)
+ */
+void
+index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor,
+				   Datum *values, bool *isnull)
+{
+	int			i;
+
+	/* Assert to protect callers who allocate fixed-size arrays */
+	Assert(tupleDescriptor->natts <= INDEX_MAX_KEYS);
+
+	for (i = 0; i < tupleDescriptor->natts; i++)
+	{
+		values[i] = index_getattr(tup, i + 1, tupleDescriptor, &isnull[i]);
+	}
+}
+
 /*
  * Create a palloc'd copy of an index tuple.
  */

src/backend/access/index/genam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/index/genam.c,v 1.74 2009/06/11 14:48:54 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/index/genam.c,v 1.75 2009/08/01 19:59:41 tgl Exp $
  *
  * NOTES
  *	  many of the old access method routines have been turned into
@@ -24,6 +24,8 @@
 #include "miscadmin.h"
 #include "pgstat.h"
 #include "storage/bufmgr.h"
+#include "utils/builtins.h"
+#include "utils/lsyscache.h"
 #include "utils/rel.h"
 #include "utils/tqual.h"
 
@@ -130,6 +132,59 @@ IndexScanEnd(IndexScanDesc scan)
 	pfree(scan);
 }
 
+/*
+ * ReportUniqueViolation -- Report a unique-constraint violation.
+ *
+ * The index entry represented by values[]/isnull[] violates the unique
+ * constraint enforced by this index.  Throw a suitable error.
+ */
+void
+ReportUniqueViolation(Relation indexRelation, Datum *values, bool *isnull)
+{
+	/*
+	 * XXX for the moment we use the index's tupdesc as a guide to the
+	 * datatypes of the values.  This is okay for btree indexes but is in
+	 * fact the wrong thing in general.  This will have to be fixed if we
+	 * are ever to support non-btree unique indexes.
+	 */
+	TupleDesc	tupdesc = RelationGetDescr(indexRelation);
+	char	   *key_names;
+	StringInfoData key_values;
+	int			i;
+
+	key_names = pg_get_indexdef_columns(RelationGetRelid(indexRelation), true);
+
+	/* Get printable versions of the key values */
+	initStringInfo(&key_values);
+	for (i = 0; i < tupdesc->natts; i++)
+	{
+		char   *val;
+
+		if (isnull[i])
+			val = "null";
+		else
+		{
+			Oid		foutoid;
+			bool	typisvarlena;
+
+			getTypeOutputInfo(tupdesc->attrs[i]->atttypid,
+							  &foutoid, &typisvarlena);
+			val = OidOutputFunctionCall(foutoid, values[i]);
+		}
+
+		if (i > 0)
+			appendStringInfoString(&key_values, ", ");
+		appendStringInfoString(&key_values, val);
+	}
+
+	ereport(ERROR,
+			(errcode(ERRCODE_UNIQUE_VIOLATION),
+			 errmsg("duplicate key value violates unique constraint \"%s\"",
+					RelationGetRelationName(indexRelation)),
+			 errdetail("Key (%s)=(%s) already exists.",
+					   key_names, key_values.data)));
+}
+
 
 /* ----------------------------------------------------------------
  *		heap-or-index-scan access to system catalogs

src/backend/access/nbtree/nbtinsert.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.171 2009/07/29 20:56:18 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.172 2009/08/01 19:59:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -362,12 +362,25 @@ _bt_check_unique(Relation rel, IndexTuple itup, Relation heapRel,
 					}
 
 					/*
-					 * This is a definite conflict.
+					 * This is a definite conflict.  Break the tuple down
+					 * into datums and report the error.  But first, make
+					 * sure we release the buffer locks we're holding ---
+					 * the error reporting code could make catalog accesses,
+					 * which in the worst case might touch this same index
+					 * and cause deadlocks.
 					 */
-					ereport(ERROR,
-							(errcode(ERRCODE_UNIQUE_VIOLATION),
-							 errmsg("duplicate key value violates unique constraint \"%s\"",
-									RelationGetRelationName(rel))));
+					if (nbuf != InvalidBuffer)
+						_bt_relbuf(rel, nbuf);
+					_bt_relbuf(rel, buf);
+
+					{
+						Datum	values[INDEX_MAX_KEYS];
+						bool	isnull[INDEX_MAX_KEYS];
+
+						index_deform_tuple(itup, RelationGetDescr(rel),
+										   values, isnull);
+						ReportUniqueViolation(rel, values, isnull);
+					}
 				}
 				else if (all_dead)
 				{