clarify TODO for whitebox disable_wal=1 in db_crashtest.py

tools/db_crashtest.py

@@ -318,10 +318,20 @@ def is_direct_io_supported(dbname):
 }
 
 whitebox_default_params = {
-    # TODO: enable this once we figure out how to adjust kill odds for WAL-
-    # disabled runs, and either (1) separate full `db_stress` runs out of
-    # whitebox crash or (2) support verification at end of `db_stress` runs
-    # that ran with WAL disabled.
+    # TODO: enable this at random once we figure out two things. First, we need
+    # to ensure the kill odds in WAL-disabled runs result in regular crashing
+    # before the fifteen minute timeout. When WAL is disabled there are very few
+    # calls to write functions since writes to SST files are buffered and other
+    # writes (e.g., MANIFEST) are infrequent. Crashing in reasonable time might
+    # currently assume killpoints in write functions are reached frequently.
+    #
+    # Second, we need to make sure disabling WAL actually makes a difference for
+    # `db_stress` runs where it is disabled. In particular, the full `db_stress`
+    # runs in the second half of the whitebox crash test need to run with
+    # `-reopen > 0` in order for `-wal_disabled` to make any difference.
+    # However, `-wal_disabled=1` is currently unsupported with any reopening.
+    # This issue could be resolved by adding the reopening support, or by moving
+    # the full `db_stress` runs out of the whitebox crash test.
     "disable_wal": 0,
     "duration": 10000,
     "log2_keys_per_lock": 10,