Expose message-bytes-limit in config

distributed/distributed-schema.yaml

@@ -339,6 +339,17 @@ properties:
               To avoid this, Dask usually used a file-based lock.
               However, on some systems file-based locks don't work.
               This is particularly common on HPC NFS systems, where users may want to set this to false.
+          transfer:
+            type: object
+            description: |
+              Configuration setting for data transfer between workers
+            properties:
+              message-bytes-limit:
+                type:
+                  - string
+                  - integer
+                description: |
+                  The maximum size of a message sent between workers
           connections:
             type: object
             description: |

distributed/distributed.yaml

@@ -78,6 +78,8 @@ distributed:
     blocked-handlers: []
     multiprocessing-method: spawn
     use-file-locking: True
+    transfer:
+      message-bytes-limit: 50MB
     connections:            # Maximum concurrent connections for data
       outgoing: 50          # This helps to control network saturation
       incoming: 10

distributed/tests/test_worker.py

@@ -673,8 +673,8 @@ async def test_clean(c, s, a, b):
 @gen_cluster(client=True)
 async def test_message_breakup(c, s, a, b):
     n = 100_000
-    a.state.transfer_message_target_bytes = 10 * n
-    b.state.transfer_message_target_bytes = 10 * n
+    a.state.transfer_message_bytes_limit = 10 * n
+    b.state.transfer_message_bytes_limit = 10 * n
     xs = [
         c.submit(mul, b"%d" % i, n, key=f"x{i}", workers=[a.address]) for i in range(30)
     ]
@@ -809,10 +809,10 @@ async def test_multiple_transfers(c, s, w1, w2, w3):
 @gen_cluster(client=True, nthreads=[("127.0.0.1", 1)] * 3)
 async def test_share_communication(c, s, w1, w2, w3):
     x = c.submit(
-        mul, b"1", int(w3.transfer_message_target_bytes + 1), workers=w1.address
+        mul, b"1", int(w3.transfer_message_bytes_limit + 1), workers=w1.address
     )
     y = c.submit(
-        mul, b"2", int(w3.transfer_message_target_bytes + 1), workers=w2.address
+        mul, b"2", int(w3.transfer_message_bytes_limit + 1), workers=w2.address
     )
     await wait([x, y])
     await c._replicate([x, y], workers=[w1.address, w2.address])
@@ -826,8 +826,8 @@ async def test_share_communication(c, s, w1, w2, w3):
 @pytest.mark.xfail(reason="very high flakiness")
 @gen_cluster(client=True)
 async def test_dont_overlap_communications_to_same_worker(c, s, a, b):
-    x = c.submit(mul, b"1", int(b.transfer_message_target_bytes + 1), workers=a.address)
-    y = c.submit(mul, b"2", int(b.transfer_message_target_bytes + 1), workers=a.address)
+    x = c.submit(mul, b"1", int(b.transfer_message_bytes_limit + 1), workers=a.address)
+    y = c.submit(mul, b"2", int(b.transfer_message_bytes_limit + 1), workers=a.address)
     await wait([x, y])
     z = c.submit(add, x, y, workers=b.address)
     await wait(z)
@@ -3001,9 +3001,9 @@ async def test_acquire_replicas_with_no_priority(c, s, a, b):
 @gen_cluster(client=True, nthreads=[("", 1)])
 async def test_acquire_replicas_large_data(c, s, a):
     """When acquire-replicas is used to acquire multiple sizeable tasks, it respects
-    transfer_message_target_bytes and acquires them over multiple iterations.
+    transfer_message_bytes_limit and acquires them over multiple iterations.
     """
-    size = a.state.transfer_message_target_bytes // 5 - 10_000
+    size = a.state.transfer_message_bytes_limit // 5 - 10_000
 
     class C:
         def __sizeof__(self):

distributed/tests/test_worker_state_machine.py

@@ -1013,13 +1013,13 @@ async def test_deprecated_worker_attributes(s, a, b):
 @pytest.mark.parametrize(
     "nbytes,n_in_flight",
     [
-        # Note: transfer_message_target_bytes = 50e6 bytes
         (int(10e6), 3),
         (int(20e6), 2),
         (int(30e6), 1),
     ],
 )
 def test_aggregate_gather_deps(ws, nbytes, n_in_flight):
+    ws.transfer_message_bytes_limit = int(50e6)
     ws2 = "127.0.0.1:2"
     instructions = ws.handle_stimulus(
         AcquireReplicasEvent(
@@ -1066,7 +1066,7 @@ def test_gather_priority(ws):
             },
             # Substantial nbytes prevents transfer_incoming_count_limit to be
             # overridden by transfer_incoming_bytes_throttle_threshold,
-            # but it's less than transfer_message_target_bytes
+            # but it's less than transfer_message_bytes_limit
             nbytes={f"x{i}": 4 * 2**20 for i in range(1, 9)},
             stimulus_id="compute1",
         ),

distributed/worker.py

@@ -528,7 +528,9 @@ def __init__(
         self.transfer_outgoing_count_limit = dask.config.get(
             "distributed.worker.connections.incoming"
         )
-
+        transfer_message_bytes_limit = parse_bytes(
+            dask.config.get("distributed.worker.transfer.message-bytes-limit")
+        )
         self.threads = {}
 
         self.active_threads_lock = threading.Lock()
@@ -767,6 +769,7 @@ def __init__(
             validate=validate,
             transition_counter_max=transition_counter_max,
             transfer_incoming_bytes_limit=transfer_incoming_bytes_limit,
+            transfer_message_bytes_limit=transfer_message_bytes_limit,
         )
         BaseWorker.__init__(self, state)
 
@@ -889,7 +892,7 @@ def data(self) -> MutableMapping[str, Any]:
     ready = DeprecatedWorkerStateAttribute()
     tasks = DeprecatedWorkerStateAttribute()
     target_message_size = DeprecatedWorkerStateAttribute(
-        target="transfer_message_target_bytes"
+        target="transfer_message_bytes_limit"
     )
     total_out_connections = DeprecatedWorkerStateAttribute(
         target="transfer_incoming_count_limit"

distributed/worker_state_machine.py

@@ -4,6 +4,7 @@
 import asyncio
 import heapq
 import logging
+import math
 import operator
 import random
 import sys
@@ -1129,7 +1130,7 @@ class WorkerState:
     #: :meth:`BaseWorker.gather_dep`. Multiple small tasks that can be fetched from the
     #: same worker will be clustered in a single instruction as long as their combined
     #: size doesn't exceed this value.
-    transfer_message_target_bytes: int
+    transfer_message_bytes_limit: float
 
     #: All and only tasks with ``TaskState.state == 'missing'``.
     missing_dep_flight: set[TaskState]
@@ -1254,6 +1255,7 @@ def __init__(
         validate: bool = True,
         transition_counter_max: int | Literal[False] = False,
         transfer_incoming_bytes_limit: int | None = None,
+        transfer_message_bytes_limit: float = math.inf,
     ):
         self.nthreads = nthreads
 
@@ -1292,7 +1294,7 @@ def __init__(
         self.in_flight_tasks = set()
         self.executed_count = 0
         self.long_running = set()
-        self.transfer_message_target_bytes = int(50e6)  # 50 MB
+        self.transfer_message_bytes_limit = transfer_message_bytes_limit
         self.log = deque(maxlen=100_000)
         self.stimulus_log = deque(maxlen=10_000)
         self.transition_counter = 0
@@ -1635,7 +1637,7 @@ def _select_keys_for_gather(
         """Helper of _ensure_communicating.
 
         Fetch all tasks that are replicated on the target worker within a single
-        message, up to transfer_message_target_bytes or until we reach the limit
+        message, up to transfer_message_bytes_limit or until we reach the limit
         for the size of incoming data transfers.
         """
         to_gather: list[TaskState] = []
@@ -1644,10 +1646,10 @@ def _select_keys_for_gather(
         if self.transfer_incoming_bytes_limit is not None:
             bytes_left_to_fetch = min(
                 self.transfer_incoming_bytes_limit - self.transfer_incoming_bytes,
-                self.transfer_message_target_bytes,
+                self.transfer_message_bytes_limit,
             )
         else:
-            bytes_left_to_fetch = self.transfer_message_target_bytes
+            bytes_left_to_fetch = self.transfer_message_bytes_limit
 
         while available:
             ts = available.peek()

docs/source/worker-state.rst

@@ -98,9 +98,10 @@ These :class:`TaskState` objects have their state set to ``fetch``, are put in t
 network. For each dependency we select a worker at random that has that data and collect
 the dependency from that worker. To improve bandwidth, we opportunistically gather other
 dependencies of other tasks that are known to be on that worker, up to a maximum of 50MB
-of data (:attr:`~WorkerState.transfer_message_target_bytes`) - too little data and
-bandwidth suffers, too much data and responsiveness suffers. We use a fixed number of 50
-connections (:attr:`~WorkerState.transfer_incoming_count_limit`, which is in turn
+of data (:attr:`~WorkerState.transfer_message_bytes_limit`, which is acquired from the
+configuration key ``distributed.worker.transfer.message-bytes-limit``) - too little data
+and bandwidth suffers, too much data and responsiveness suffers. We use a fixed number of
+50 connections (:attr:`~WorkerState.transfer_incoming_count_limit`, which is in turn
 acquired from the configuration key ``distributed.worker.connections.outgoing``) so as
 to avoid overly-fragmenting our network bandwidth.