diff --git a/src/taskgraph/decision.py b/src/taskgraph/decision.py
index 6a37308b..5398bd70 100644
--- a/src/taskgraph/decision.py
+++ b/src/taskgraph/decision.py
@@ -74,8 +74,28 @@ def taskgraph_decision(options, parameters=None):
      * generating a set of artifacts to memorialize the graph
      * calling TaskCluster APIs to create the graph
     """
+    level = logging.INFO
     if options.get("verbose"):
-        logging.root.setLevel(logging.DEBUG)
+        level = logging.DEBUG
+
+    logging.root.setLevel(level)
+    # Handlers must have an explicit level set for them to properly filter
+    # messages from child loggers (such as the optimization log a few lines
+    # down).
+    for h in logging.root.handlers:
+        h.setLevel(level)
+
+    if not os.path.isdir(ARTIFACTS_DIR):
+        os.mkdir(ARTIFACTS_DIR)
+
+    # optimizations are difficult to debug after the fact, so we always
+    # log them at DEBUG level, and write the log as a separate artifact
+    opt_log = logging.getLogger("optimization")
+    opt_log.setLevel(logging.DEBUG)
+    opt_handler = logging.FileHandler(ARTIFACTS_DIR / "optimizations.log", mode="w")
+    if logging.root.handlers:
+        opt_handler.setFormatter(logging.root.handlers[0].formatter)
+    opt_log.addHandler(opt_handler)
 
     parameters = parameters or (
         lambda graph_config: get_decision_parameters(graph_config, options)
diff --git a/src/taskgraph/optimize/base.py b/src/taskgraph/optimize/base.py
index 917ab82a..f914e71a 100644
--- a/src/taskgraph/optimize/base.py
+++ b/src/taskgraph/optimize/base.py
@@ -24,7 +24,7 @@
 from taskgraph.util.python_path import import_sibling_modules
 from taskgraph.util.taskcluster import find_task_id_batched, status_task_batched
 
-logger = logging.getLogger(__name__)
+logger = logging.getLogger("optimization")
 registry = {}
 
 
diff --git a/src/taskgraph/optimize/strategies.py b/src/taskgraph/optimize/strategies.py
index 621e28aa..2f436c52 100644
--- a/src/taskgraph/optimize/strategies.py
+++ b/src/taskgraph/optimize/strategies.py
@@ -5,7 +5,7 @@
 from taskgraph.util.path import match as match_path
 from taskgraph.util.taskcluster import find_task_id, status_task
 
-logger = logging.getLogger(__name__)
+logger = logging.getLogger("optimization")
 
 
 @register_strategy("index-search")
diff --git a/test/test_optimize_strategies.py b/test/test_optimize_strategies.py
index 9cd408c3..2203e984 100644
--- a/test/test_optimize_strategies.py
+++ b/test/test_optimize_strategies.py
@@ -1,6 +1,7 @@
 # Any copyright is dedicated to the public domain.
 # http://creativecommons.org/publicdomain/zero/1.0/
 
+import logging
 import os
 from datetime import datetime
 from time import mktime
@@ -24,27 +25,37 @@ def params():
 
 
 @pytest.mark.parametrize(
-    "state,expires,expected",
+    "state,expires,expected,logs",
     (
         (
             "completed",
             "2021-06-06T14:53:16.937Z",
             False,
+            (
+                "not replacing {label} with {taskid} because it expires before {deadline}",
+            ),
         ),
-        ("completed", "2021-06-08T14:53:16.937Z", "abc"),
+        ("completed", "2021-06-08T14:53:16.937Z", "abc", ()),
         (
             "exception",
             "2021-06-08T14:53:16.937Z",
             False,
+            (
+                "not replacing {label} with {taskid} because it is in failed or exception state",
+            ),
         ),
         (
             "failed",
             "2021-06-08T14:53:16.937Z",
             False,
+            (
+                "not replacing {label} with {taskid} because it is in failed or exception state",
+            ),
         ),
     ),
 )
-def test_index_search(responses, params, state, expires, expected):
+def test_index_search(caplog, responses, params, state, expires, expected, logs):
+    caplog.set_level(logging.DEBUG, "optimization")
     taskid = "abc"
     index_path = "foo.bar.latest"
 
@@ -79,13 +90,27 @@ def test_index_search(responses, params, state, expires, expected):
     deadline = "2021-06-07T19:03:20.482Z"
     assert (
         opt.should_replace_task(
-            {}, params, deadline, ([index_path], label_to_taskid, taskid_to_status)
+            {"label": "task-label"},
+            params,
+            deadline,
+            ([index_path], label_to_taskid, taskid_to_status),
         )
         == expected
     )
     # test the non-batched variant as well
     assert opt.should_replace_task({}, params, deadline, [index_path]) == expected
 
+    if logs:
+        log_records = [
+            (
+                "optimization",
+                logging.DEBUG,
+                m.format(label="task-label", taskid=taskid, deadline=deadline),
+            )
+            for m in logs
+        ]
+        assert caplog.record_tuples == log_records
+
 
 @pytest.mark.parametrize(
     "params,file_patterns,should_optimize",
@@ -111,8 +136,18 @@ def test_index_search(responses, params, state, expires, expected):
         ),
     ),
 )
-def test_skip_unless_changed(params, file_patterns, should_optimize):
+def test_skip_unless_changed(caplog, params, file_patterns, should_optimize):
+    caplog.set_level(logging.DEBUG, "optimization")
     task = make_task("task")
 
     opt = SkipUnlessChanged()
     assert opt.should_remove_task(task, params, file_patterns) == should_optimize
+
+    if should_optimize:
+        assert caplog.record_tuples == [
+            (
+                "optimization",
+                logging.DEBUG,
+                f'no files found matching a pattern in `skip-unless-changed` for "{task.label}"',
+            ),
+        ]