Add "no-tsdb-found" history load length defaults

piker/data/feed.py

@@ -228,7 +228,7 @@ def diff_history(
                 # the + 1 is because ``last_tsdb_dt`` is pulled from
                 # the last row entry for the ``'time'`` field retreived
                 # from the tsdb.
-                to_push = array[abs(s_diff)+1:]
+                to_push = array[abs(s_diff) + 1:]
 
             else:
                 # pass back only the portion of the array that is
@@ -251,6 +251,7 @@ async def start_backfill(
     last_tsdb_dt: Optional[datetime] = None,
     storage: Optional[Storage] = None,
     write_tsdb: bool = True,
+    tsdb_is_up: bool = False,
 
     task_status: TaskStatus[trio.CancelScope] = trio.TASK_STATUS_IGNORED,
 
@@ -266,8 +267,8 @@ async def start_backfill(
 
         # sample period step size in seconds
         step_size_s = (
-            pendulum.from_timestamp(times[-1]) -
-            pendulum.from_timestamp(times[-2])
+            pendulum.from_timestamp(times[-1])
+            - pendulum.from_timestamp(times[-2])
         ).seconds
 
         # "frame"'s worth of sample period steps in seconds
@@ -292,25 +293,33 @@ async def start_backfill(
         # let caller unblock and deliver latest history frame
         task_status.started((shm, start_dt, end_dt, bf_done))
 
+        # based on the sample step size, maybe load a certain amount history
         if last_tsdb_dt is None:
-            # maybe a better default (they don't seem to define epoch?!)
-
-            # based on the sample step size load a certain amount
-            # history
-            if step_size_s == 1:
-                last_tsdb_dt = pendulum.now().subtract(days=2)
-
-            elif step_size_s == 60:
-                last_tsdb_dt = pendulum.now().subtract(years=2)
-
-            else:
+            if step_size_s not in (1, 60):
                 raise ValueError(
                     '`piker` only needs to support 1m and 1s sampling '
                     'but ur api is trying to deliver a longer '
                     f'timeframe of {step_size_s} ' 'seconds.. so ye, dun '
-                    'do dat bruh.'
+                    'do dat brudder.'
                 )
 
+            # when no tsdb "last datum" is provided, we just load
+            # some near-term history.
+            periods = {
+                1: {'days': 1},
+                60: {'days': 14},
+            }
+
+            if tsdb_is_up:
+                # do a decently sized backfill and load it into storage.
+                periods = {
+                    1: {'days': 6},
+                    60: {'years': 2},
+                }
+
+            kwargs = periods[step_size_s]
+            last_tsdb_dt = start_dt.subtract(**kwargs)
+
         # configure async query throttling
         erlangs = config.get('erlangs', 1)
         rate = config.get('rate', 1)