Store metadata only once for array jobs (#1042)

* store metadata only once for array jobs

* remove todo comments

* fix typo

* add troubleshooting comment to clustertools/readme

* use metadata instead of meta_data everywhere

* update changelog

cluster_tools/Changelog.md

@@ -14,6 +14,7 @@ For upgrade instructions, please check the respective *Breaking Changes* section
 ### Added
 
 ### Changed
+- Array jobs are spawned faster now, because common meta data is not serialized for each subjob. The performance improvement is especially big, when custom logging code is configured for array jobs. [#1042](https://github.com/scalableminds/webknossos-libs/pull/1042)
 - Updated ruff to v0.4.0 [1047](https://github.com/scalableminds/webknossos-libs/pull/1047)
 
 ### Fixed

cluster_tools/README.md

@@ -74,6 +74,7 @@ If you would like to configure these limits independently, you can do so by sett
 ## Dev Setup
 
 ```
+# See ./dockered-slurm/README.md for troubleshooting
 cd dockered-slurm
 docker-compose up -d
 docker exec -it slurmctld bash

cluster_tools/cluster_tools/remote.py

@@ -63,18 +63,14 @@ def worker(
         custom_main_path = get_custom_main_path(workerid, executor)
         with open(input_file_name, "rb") as f:
             unpickled_tuple = pickling.load(f, custom_main_path)
-            if len(unpickled_tuple) == 4:
-                fun, args, kwargs, meta_data = unpickled_tuple
-                output_pickle_path = executor.format_outfile_name(
-                    cfut_dir, workerid_with_idx
-                )
-            else:
-                assert len(unpickled_tuple) == 5, "Unexpected encoding"
-                fun, args, kwargs, meta_data, output_pickle_path = unpickled_tuple
-
-        if isinstance(fun, str):
-            with open(fun, "rb") as function_file:
-                fun = pickling.load(function_file, custom_main_path)
+            assert len(unpickled_tuple) == 4, "Unexpected encoding"
+            fun_and_metadata, args, kwargs, output_pickle_path = unpickled_tuple
+
+        if isinstance(fun_and_metadata, str):
+            with open(fun_and_metadata, "rb") as function_file:
+                fun, meta_data = pickling.load(function_file, custom_main_path)
+        else:
+            fun, meta_data = fun_and_metadata
 
         setup_logging(meta_data, executor, cfut_dir)
 

cluster_tools/cluster_tools/schedulers/cluster_executor.py

@@ -148,14 +148,14 @@ def __init__(
             partial(_handle_kill_through_weakref, ref(self), existing_sigint_handler),
         )
 
-        self.meta_data = {}
+        self.metadata = {}
         assert not (
             "logging_config" in kwargs and "logging_setup_fn" in kwargs
         ), "Specify either logging_config OR logging_setup_fn but not both at once"
         if "logging_config" in kwargs:
-            self.meta_data["logging_config"] = kwargs["logging_config"]
+            self.metadata["logging_config"] = kwargs["logging_config"]
         if "logging_setup_fn" in kwargs:
-            self.meta_data["logging_setup_fn"] = kwargs["logging_setup_fn"]
+            self.metadata["logging_setup_fn"] = kwargs["logging_setup_fn"]
 
     @classmethod
     def as_completed(cls, futs: List["Future[_T]"]) -> Iterator["Future[_T]"]:
@@ -412,7 +412,7 @@ def submit(  # type: ignore[override]
 
         # Start the job.
         serialized_function_info = pickling.dumps(
-            (__fn, args, kwargs, self.meta_data, output_pickle_path)
+            ((__fn, self.metadata), args, kwargs, output_pickle_path)
         )
         with open(self.format_infile_name(self.cfut_dir, workerid), "wb") as f:
             f.write(serialized_function_info)
@@ -451,9 +451,10 @@ def get_workerid_with_index(cls, workerid: str, index: Union[int, str]) -> str:
     def get_jobid_with_index(cls, jobid: Union[str, int], index: int) -> str:
         return f"{jobid}_{index}"
 
-    def get_function_pickle_path(self, workerid: str) -> str:
+    def get_function_and_metadata_pickle_path(self, workerid: str) -> str:
         return self.format_infile_name(
-            self.cfut_dir, self.get_workerid_with_index(workerid, "function")
+            self.cfut_dir,
+            self.get_workerid_with_index(workerid, "function-and-metadata"),
         )
 
     @staticmethod
@@ -484,10 +485,12 @@ def map_to_futures(
         futs_with_output_paths = []
         workerid = random_string()
 
-        pickled_function_path = self.get_function_pickle_path(workerid)
-        self.files_to_clean_up.append(pickled_function_path)
-        with open(pickled_function_path, "wb") as file:
-            pickling.dump(fn, file)
+        pickled_function_and_metadata_path = self.get_function_and_metadata_pickle_path(
+            workerid
+        )
+        self.files_to_clean_up.append(pickled_function_and_metadata_path)
+        with open(pickled_function_and_metadata_path, "wb") as file:
+            pickling.dump((fn, self.metadata), file)
         self.store_main_path_to_meta_file(workerid)
 
         for index, arg in enumerate(args):
@@ -511,7 +514,12 @@ def map_to_futures(
                 os.unlink(preliminary_output_pickle_path)
 
             serialized_function_info = pickling.dumps(
-                (pickled_function_path, [arg], {}, self.meta_data, output_pickle_path)
+                (
+                    pickled_function_and_metadata_path,
+                    [arg],
+                    {},
+                    output_pickle_path,
+                )
             )
             infile_name = self.format_infile_name(self.cfut_dir, workerid_with_index)