Add an extra header byte to TOAST-pointer datums to represent their size

explicitly.  This means a TOAST pointer takes 18 bytes instead of 17 --- still
smaller than in 8.2 --- which seems a good tradeoff to ensure we won't have
painted ourselves into a corner if we want to support multiple types of TOAST
pointer later on.  Per discussion with Greg Stark.

1 files changed, 28 insertions, 17 deletions

diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index 2d09b773614..d2f1dfafd4a 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.75 2007/09/26 23:29:10 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.76 2007/09/30 19:54:58 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -52,6 +52,21 @@
 #define VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer) \
 	((toast_pointer).va_extsize < (toast_pointer).va_rawsize - VARHDRSZ)
 
+/*
+ * Macro to fetch the possibly-unaligned contents of an EXTERNAL datum
+ * into a local "struct varatt_external" toast pointer.  This should be
+ * just a memcpy, but some versions of gcc seem to produce broken code
+ * that assumes the datum contents are aligned.  Introducing an explicit
+ * intermediate "varattrib_1b_e *" variable seems to fix it.
+ */
+#define VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr) \
+do { \
+	varattrib_1b_e *attre = (varattrib_1b_e *) (attr); \
+	Assert(VARSIZE_ANY_EXHDR(attre) == sizeof(toast_pointer)); \
+	memcpy(&(toast_pointer), VARDATA_EXTERNAL(attre), sizeof(toast_pointer)); \
+} while (0)
+
+
 static void toast_delete_datum(Relation rel, Datum value);
 static Datum toast_save_datum(Relation rel, Datum value,
 							  bool use_wal, bool use_fsm);
@@ -172,7 +187,7 @@ heap_tuple_untoast_attr_slice(struct varlena *attr,
 	{
 		struct varatt_external toast_pointer;
 
-		memcpy(&toast_pointer, VARDATA_SHORT(attr), sizeof(toast_pointer));
+		VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 
 		/* fast path for non-compressed external datums */
 		if (!VARATT_EXTERNAL_IS_COMPRESSED(toast_pointer))
@@ -249,7 +264,7 @@ toast_raw_datum_size(Datum value)
 		/* va_rawsize is the size of the original datum -- including header */
 		struct varatt_external toast_pointer;
 
-		memcpy(&toast_pointer, VARDATA_SHORT(attr), sizeof(toast_pointer));
+		VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 		result = toast_pointer.va_rawsize;
 	}
 	else if (VARATT_IS_COMPRESSED(attr))
@@ -294,7 +309,7 @@ toast_datum_size(Datum value)
 		 */
 		struct varatt_external toast_pointer;
 
-		memcpy(&toast_pointer, VARDATA_SHORT(attr), sizeof(toast_pointer));
+		VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 		result = toast_pointer.va_extsize;
 	}
 	else if (VARATT_IS_SHORT(attr))
@@ -470,9 +485,8 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
 				VARATT_IS_EXTERNAL(old_value))
 			{
 				if (toast_isnull[i] || !VARATT_IS_EXTERNAL(new_value) ||
-					memcmp(VARDATA_SHORT(old_value),
-						   VARDATA_SHORT(new_value),
-						   sizeof(struct varatt_external)) != 0)
+					memcmp((char *) old_value, (char *) new_value, 
+						   VARSIZE_EXTERNAL(old_value)) != 0)
 				{
 					/*
 					 * The old external stored value isn't needed any more
@@ -1071,7 +1085,7 @@ toast_save_datum(Relation rel, Datum value,
 	Datum		t_values[3];
 	bool		t_isnull[3];
 	CommandId	mycid = GetCurrentCommandId();
-	struct varlena *result;
+	varattrib_pointer *result;
 	struct varatt_external toast_pointer;
 	struct
 	{
@@ -1192,9 +1206,9 @@ toast_save_datum(Relation rel, Datum value,
 	/*
 	 * Create the TOAST pointer value that we'll return
 	 */
-	result = (struct varlena *) palloc(sizeof(varattrib_pointer));
-	SET_VARSIZE_EXTERNAL(result);
-	memcpy(VARDATA_SHORT(result), &toast_pointer, sizeof(toast_pointer));
+	result = (varattrib_pointer *) palloc(sizeof(varattrib_pointer));
+	SET_VARSIZE_EXTERNAL(result, sizeof(varattrib_pointer));
+	memcpy(VARDATA_EXTERNAL(result), &toast_pointer, sizeof(toast_pointer));
 
 	return PointerGetDatum(result);
 }
@@ -1221,8 +1235,7 @@ toast_delete_datum(Relation rel, Datum value)
 		return;
 
 	/* Must copy to access aligned fields */
-	memcpy(&toast_pointer, VARDATA_SHORT(attr),
-		   sizeof(struct varatt_external));
+	VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 
 	/*
 	 * Open the toast relation and its index
@@ -1289,8 +1302,7 @@ toast_fetch_datum(struct varlena *attr)
 	int32		chunksize;
 
 	/* Must copy to access aligned fields */
-	memcpy(&toast_pointer, VARDATA_SHORT(attr),
-		   sizeof(struct varatt_external));
+	VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 
 	ressize = toast_pointer.va_extsize;
 	numchunks = ((ressize - 1) / TOAST_MAX_CHUNK_SIZE) + 1;
@@ -1452,8 +1464,7 @@ toast_fetch_datum_slice(struct varlena *attr, int32 sliceoffset, int32 length)
 	Assert(VARATT_IS_EXTERNAL(attr));
 
 	/* Must copy to access aligned fields */
-	memcpy(&toast_pointer, VARDATA_SHORT(attr),
-		   sizeof(struct varatt_external));
+	VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
 
 	/*
 	 * It's nonsense to fetch slices of a compressed datum -- this isn't lo_*