pg_column_toast_chunk_id.patch

diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 5778e3f0ef..4ddcf885cd 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -5070,6 +5070,47 @@ pg_column_compression(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(cstring_to_text(result));
 }
 
+/*
+ * Return the chunk id of the TOASTed value.
+ * Return NULL for unTOASTed value.
+ */
+Datum
+pg_column_toast_chunk_id(PG_FUNCTION_ARGS)
+{
+	int			typlen;
+	struct varlena *attr;
+	struct varatt_external toast_pointer;
+
+	/* On first call, get the input type's typlen, and save at *fn_extra */
+	if (fcinfo->flinfo->fn_extra == NULL)
+	{
+		/* Lookup the datatype of the supplied argument */
+		Oid			argtypeid = get_fn_expr_argtype(fcinfo->flinfo, 0);
+
+		typlen = get_typlen(argtypeid);
+		if (typlen == 0)		/* should not happen */
+			elog(ERROR, "cache lookup failed for type %u", argtypeid);
+
+		fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
+													  sizeof(int));
+		*((int *) fcinfo->flinfo->fn_extra) = typlen;
+	}
+	else
+		typlen = *((int *) fcinfo->flinfo->fn_extra);
+
+	if (typlen != -1)
+		PG_RETURN_NULL();
+
+	attr = (struct varlena *) DatumGetPointer(PG_GETARG_DATUM(0));
+
+	if (!VARATT_IS_EXTERNAL_ONDISK(attr))
+		PG_RETURN_NULL();
+
+	VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
+
+	PG_RETURN_OID(toast_pointer.va_valueid);
+}
+
 /*
  * string_agg - Concatenates values and returns string.
  *
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 7c358cff16..4c214f4c63 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7414,6 +7414,9 @@
 { oid => '2121', descr => 'compression method for the compressed datum',
   proname => 'pg_column_compression', provolatile => 's', prorettype => 'text',
   proargtypes => 'any', prosrc => 'pg_column_compression' },
+{ oid => '8393', descr => 'chunk ID of TOASTed value',
+  proname => 'pg_column_toast_chunk_id', provolatile => 's', prorettype => 'oid',
+  proargtypes => 'any', prosrc => 'pg_column_toast_chunk_id' },
 { oid => '2322',
   descr => 'total disk space usage for the specified tablespace',
   proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',