Updates to cache policies

src/prefect/records/cache_policies.py → src/prefect/cache_policies.py

@@ -8,6 +8,10 @@
 
 @dataclass
 class CachePolicy:
+    """
+    Base class for all cache policies.
+    """
+
     @classmethod
     def from_cache_key_fn(
         cls, cache_key_fn: Callable[["TaskRunContext", Dict[str, Any]], Optional[str]]
@@ -59,6 +63,11 @@ def __add__(self, other: "CachePolicy") -> "CompoundCachePolicy":
 
 @dataclass
 class CacheKeyFnPolicy(CachePolicy):
+    """
+    This policy accepts a custom function with signature f(task_run_context, task_parameters, flow_parameters) -> str
+    and uses it to compute a task run cache key.
+    """
+
     # making it optional for tests
     cache_key_fn: Optional[
         Callable[["TaskRunContext", Dict[str, Any]], Optional[str]]
@@ -77,6 +86,13 @@ def compute_key(
 
 @dataclass
 class CompoundCachePolicy(CachePolicy):
+    """
+    This policy is constructed from two or more other cache policies and works by computing the keys
+    for each policy individually, and then hashing a sorted tuple of all computed keys.
+
+    Any keys that return `None` will be ignored.
+    """
+
     policies: Optional[list] = None
 
     def compute_key(
@@ -88,20 +104,25 @@ def compute_key(
     ) -> Optional[str]:
         keys = []
         for policy in self.policies or []:
-            keys.append(
-                policy.compute_key(
-                    task_ctx=task_ctx,
-                    inputs=inputs,
-                    flow_parameters=flow_parameters,
-                    **kwargs,
-                )
+            policy_key = policy.compute_key(
+                task_ctx=task_ctx,
+                inputs=inputs,
+                flow_parameters=flow_parameters,
+                **kwargs,
             )
+            if policy_key is not None:
+                keys.append(policy_key)
+        if not keys:
+            return None
         return hash_objects(*keys)
 
 
 @dataclass
-class Default(CachePolicy):
-    "Execution run ID only"
+class _None(CachePolicy):
+    """
+    Policy that always returns `None` for the computed cache key.
+    This policy prevents persistence.
+    """
 
     def compute_key(
         self,
@@ -110,12 +131,14 @@ def compute_key(
         flow_parameters: Dict[str, Any],
         **kwargs,
     ) -> Optional[str]:
-        return str(task_ctx.task_run.id)
+        return None
 
 
 @dataclass
-class _None(CachePolicy):
-    "ignore key policies altogether, always run - prevents persistence"
+class TaskSource(CachePolicy):
+    """
+    Policy for computing a cache key based on the source code of the task.
+    """
 
     def compute_key(
         self,
@@ -124,33 +147,60 @@ def compute_key(
         flow_parameters: Dict[str, Any],
         **kwargs,
     ) -> Optional[str]:
-        return None
+        if not task_ctx:
+            return None
+        try:
+            lines = inspect.getsource(task_ctx.task)
+        except TypeError:
+            lines = inspect.getsource(task_ctx.task.fn.__class__)
+
+        return hash_objects(lines)
 
 
 @dataclass
-class TaskDef(CachePolicy):
+class FlowParameters(CachePolicy):
+    """
+    Policy that computes the cache key based on a hash of the flow parameters.
+    """
+
     def compute_key(
         self,
         task_ctx: TaskRunContext,
         inputs: Dict[str, Any],
         flow_parameters: Dict[str, Any],
         **kwargs,
     ) -> Optional[str]:
-        lines = inspect.getsource(task_ctx.task)
-        return hash_objects(lines)
+        if not flow_parameters:
+            return None
+        return hash_objects(flow_parameters)
 
 
 @dataclass
-class FlowParameters(CachePolicy):
-    pass
+class RunId(CachePolicy):
+    """
+    Returns either the prevailing flow run ID, or if not found, the prevailing task
+    run ID.
+    """
+
+    def compute_key(
+        self,
+        task_ctx: TaskRunContext,
+        inputs: Dict[str, Any],
+        flow_parameters: Dict[str, Any],
+        **kwargs,
+    ) -> Optional[str]:
+        if not task_ctx:
+            return None
+        run_id = task_ctx.task_run.flow_run_id
+        if run_id is None:
+            run_id = task_ctx.task_run.id
+        return str(run_id)
 
 
 @dataclass
 class Inputs(CachePolicy):
     """
-    Exposes flag for whether to include flow parameters as well.
-
-    And exclude/include config.
+    Policy that computes a cache key based on a hash of the runtime inputs provided to the task..
     """
 
     exclude: Optional[list] = None
@@ -166,14 +216,19 @@ def compute_key(
         inputs = inputs or {}
         exclude = self.exclude or []
 
+        if not inputs:
+            return None
+
         for key, val in inputs.items():
             if key not in exclude:
                 hashed_inputs[key] = val
 
         return hash_objects(hashed_inputs)
 
 
-DEFAULT = Default()
 INPUTS = Inputs()
 NONE = _None()
-TASKDEF = TaskDef()
+TASK_SOURCE = TaskSource()
+FLOW_PARAMETERS = FlowParameters()
+RUN_ID = RunId()
+DEFAULT = INPUTS + TASK_SOURCE + RUN_ID

src/prefect/task_engine.py

@@ -174,11 +174,18 @@ def call_hooks(self, state: State = None) -> Iterable[Callable]:
     def compute_transaction_key(self) -> str:
         key = None
         if self.task.cache_policy:
+            flow_run_context = FlowRunContext.get()
             task_run_context = TaskRunContext.get()
+
+            if flow_run_context:
+                parameters = flow_run_context.parameters
+            else:
+                parameters = None
+
             key = self.task.cache_policy.compute_key(
                 task_ctx=task_run_context,
                 inputs=self.parameters,
-                flow_parameters=None,
+                flow_parameters=parameters,
             )
         elif self.task.result_storage_key is not None:
             key = _format_user_supplied_storage_key(self.task.result_storage_key)

src/prefect/tasks.py

@@ -32,6 +32,7 @@
 
 from typing_extensions import Literal, ParamSpec
 
+from prefect.cache_policies import DEFAULT, NONE, CachePolicy
 from prefect.client.orchestration import get_client
 from prefect.client.schemas import TaskRun
 from prefect.client.schemas.objects import TaskRunInput, TaskRunResult
@@ -44,7 +45,6 @@
 )
 from prefect.futures import PrefectDistributedFuture, PrefectFuture
 from prefect.logging.loggers import get_logger
-from prefect.records.cache_policies import DEFAULT, NONE, CachePolicy
 from prefect.results import ResultFactory, ResultSerializer, ResultStorage
 from prefect.settings import (
     PREFECT_TASK_DEFAULT_RETRIES,

tests/records/test_cache_policies.py → tests/test_cache_policies.py

@@ -1,13 +1,16 @@
 import itertools
+from dataclasses import dataclass
+from typing import Callable
 
 import pytest
 
-from prefect.records.cache_policies import (
+from prefect.cache_policies import (
+    DEFAULT,
     CachePolicy,
     CompoundCachePolicy,
-    Default,
     Inputs,
-    TaskDef,
+    RunId,
+    TaskSource,
     _None,
 )
 
@@ -40,26 +43,6 @@ def test_addition_of_none_is_noop(self, typ):
         assert policy + other == other
 
 
-class TestDefaultPolicy:
-    def test_initializes(self):
-        policy = Default()
-        assert isinstance(policy, CachePolicy)
-
-    def test_returns_run_id(self):
-        class Run:
-            id = "foo"
-
-        class TaskCtx:
-            pass
-
-        task_ctx = TaskCtx()
-        task_ctx.task_run = Run()
-
-        policy = Default()
-        key = policy.compute_key(task_ctx=task_ctx, inputs=None, flow_parameters=None)
-        assert key == "foo"
-
-
 class TestInputsPolicy:
     def test_initializes(self):
         policy = Inputs()
@@ -133,7 +116,7 @@ def test_initializes(self):
         assert isinstance(policy, CachePolicy)
 
     def test_creation_via_addition(self):
-        one, two = Inputs(), Default()
+        one, two = Inputs(), TaskSource()
         policy = one + two
         assert isinstance(policy, CompoundCachePolicy)
 
@@ -152,18 +135,29 @@ def test_subtraction_creates_new_policies(self):
         assert policy.policies != new_policy.policies
 
     def test_creation_via_subtraction(self):
-        one = Default()
+        one = RunId()
         policy = one - "foo"
         assert isinstance(policy, CompoundCachePolicy)
 
+    def test_nones_are_ignored(self):
+        one, two = _None(), _None()
+        policy = CompoundCachePolicy(policies=[one, two])
+        assert isinstance(policy, CompoundCachePolicy)
+
+        fparams = dict(x=42, y="foo")
+        compound_key = policy.compute_key(
+            task_ctx=None, inputs=dict(z=[1, 2]), flow_parameters=fparams
+        )
+        assert compound_key is None
+
 
-class TestTaskDefPolicy:
+class TestTaskSourcePolicy:
     def test_initializes(self):
-        policy = TaskDef()
+        policy = TaskSource()
         assert isinstance(policy, CachePolicy)
 
     def test_changes_in_def_change_key(self):
-        policy = TaskDef()
+        policy = TaskSource()
 
         class TaskCtx:
             pass
@@ -189,3 +183,77 @@ def my_func(x):
         )
 
         assert key != new_key
+
+
+class TestDefaultPolicy:
+    def test_changing_the_inputs_busts_the_cache(self):
+        inputs = dict(x=42)
+        key = DEFAULT.compute_key(task_ctx=None, inputs=inputs, flow_parameters=None)
+
+        inputs = dict(x=43)
+        new_key = DEFAULT.compute_key(
+            task_ctx=None, inputs=inputs, flow_parameters=None
+        )
+
+        assert key != new_key
+
+    def test_changing_the_run_id_busts_the_cache(self):
+        @dataclass
+        class Run:
+            id: str
+            flow_run_id: str = None
+
+        def my_task():
+            pass
+
+        @dataclass
+        class TaskCtx:
+            task_run: Run
+            task = my_task
+
+        task_run_a = Run(id="a", flow_run_id="a")
+        task_run_b = Run(id="b", flow_run_id="b")
+        task_run_c = Run(id="c", flow_run_id=None)
+        task_run_d = Run(id="d", flow_run_id=None)
+
+        key_a = DEFAULT.compute_key(
+            task_ctx=TaskCtx(task_run=task_run_a), inputs=None, flow_parameters=None
+        )
+        key_b = DEFAULT.compute_key(
+            task_ctx=TaskCtx(task_run=task_run_b), inputs=None, flow_parameters=None
+        )
+        key_c = DEFAULT.compute_key(
+            task_ctx=TaskCtx(task_run=task_run_c), inputs=None, flow_parameters=None
+        )
+        key_d = DEFAULT.compute_key(
+            task_ctx=TaskCtx(task_run=task_run_d), inputs=None, flow_parameters=None
+        )
+
+        assert key_a not in [key_b, key_c, key_d]
+        assert key_b not in [key_a, key_c, key_d]
+        assert key_c not in [key_a, key_b, key_d]
+        assert key_d not in [key_a, key_b, key_c]
+
+    def test_changing_the_source_busts_the_cache(self):
+        @dataclass
+        class Run:
+            id: str
+            flow_run_id: str = None
+
+        @dataclass
+        class TaskCtx:
+            task_run: Run
+            task: Callable = None
+
+        task_run = Run(id="a", flow_run_id="b")
+        ctx_one = TaskCtx(task_run=task_run, task=lambda: "foo")
+        ctx_two = TaskCtx(task_run=task_run, task=lambda: "bar")
+
+        key_one = DEFAULT.compute_key(
+            task_ctx=ctx_one, inputs=None, flow_parameters=None
+        )
+        key_two = DEFAULT.compute_key(
+            task_ctx=ctx_two, inputs=None, flow_parameters=None
+        )
+
+        assert key_one != key_two