Fix default_transaction_isolation on system/database level

edb/edgeql/compiler/config.py

@@ -146,7 +146,24 @@ def compile_ConfigReset(
             span=expr.span,
         )
 
-    elif isinstance(info.param_type, s_objtypes.ObjectType):
+    if (
+        expr.scope == qltypes.ConfigScope.INSTANCE and
+        info.backend_setting == 'default_transaction_isolation'
+    ):
+        # Special case for default_transaction_isolation:
+        # Gel default is `serializable`, while PG default is `read committed`.
+        default = info.ptr.get_default(ctx.env.schema)
+        if default is not None:
+            return compile_ConfigSet(
+                qlast.ConfigSet(
+                    name=expr.name,
+                    scope=expr.scope,
+                    expr=default.parse(),
+                ),
+                ctx=ctx,
+            )
+
+    if isinstance(info.param_type, s_objtypes.ObjectType):
         param_type_name = info.param_type.get_name(ctx.env.schema)
         param_type_ref = qlast.ObjectRef(
             name=param_type_name.name,

edb/server/bootstrap.py

@@ -1974,6 +1974,7 @@ async def _configure(
     await _execute_block(ctx.conn, block)
 
     backend_params = ctx.cluster.get_runtime_params()
+    need_reload = False
     for setname in config_spec:
         setting = config_spec[setname]
         if (
@@ -1984,9 +1985,12 @@ async def _configure(
                 # backends that don't support it.
                 # TODO: this should be replaced by instance-wide
                 #       emulation at backend connection time.
+                #       fantix: +1 to the above, also needed by
+                #       `default_transaction_isolation=serializable`
                 backend_params.has_configfile_access
             )
         ):
+            need_reload = True
             script = qlcodegen.generate_source(
                 qlast.ConfigSet(
                     name=qlast.ObjectRef(name=setting.name),
@@ -1996,6 +2000,8 @@ async def _configure(
             )
             schema, sql = compile_bootstrap_script(compiler, schema, script)
             await _execute(ctx.conn, sql)
+    if need_reload:
+        await _execute(ctx.conn, 'SELECT pg_reload_conf()')
 
 
 def compile_sys_queries(

edb/server/pgcluster.py

@@ -87,7 +87,6 @@
     'timezone': 'UTC',
     'intervalstyle': 'iso_8601',
     'jit': 'off',
-    'default_transaction_isolation': 'serializable',
 }
 
 
@@ -497,6 +496,7 @@ async def ensure_initialized(self, **settings: Any) -> bool:
 
             have_c_utf8 = self.get_runtime_params().has_c_utf8_locale
             await self.init(
+                "default_transaction_isolation='serializable'",
                 username='postgres',
                 locale='C.UTF-8' if have_c_utf8 else 'en_US.UTF-8',
                 lc_collate='C',
@@ -513,16 +513,18 @@ async def ensure_initialized(self, **settings: Any) -> bool:
         else:
             return False
 
-    async def init(self, **settings: str) -> None:
+    async def init(self, *server_config: str, **settings: str) -> None:
         """Initialize cluster."""
         if await self.get_status() != 'not-initialized':
             raise ClusterError(
                 'cluster in {!r} has already been initialized'.format(
                     self._data_dir))
 
-        if settings:
+        if settings or server_config:
             settings_args = ['--{}={}'.format(k.replace('_', '-'), v)
                              for k, v in settings.items()]
+            for conf in server_config:
+                settings_args.append('-c {}'.format(conf))
             extra_args = ['-o'] + [' '.join(settings_args)]
         else:
             extra_args = []