diff --git a/piker/data/feed.py b/piker/data/feed.py
index 9ab98600..6cbfbebc 100644
--- a/piker/data/feed.py
+++ b/piker/data/feed.py
@@ -36,6 +36,7 @@ from trio.abc import ReceiveChannel
 from trio_typing import TaskStatus
 import tractor
 from pydantic import BaseModel
+import numpy as np
 
 from ..brokers import get_brokermod
 from .._cacheables import maybe_open_context
@@ -276,13 +277,38 @@ async def manage_history(
                 # TODO: this should be used verbatim for the pure
                 # shm backfiller approach below.
 
+                def diff_history(
+                    array,
+                    start_dt,
+                    end_dt,
+
+                ) -> np.ndarray:
+
+                    s_diff = (last_tsdb_dt - start_dt).seconds
+
+                    # if we detect a partial frame's worth of data
+                    # that is new, slice out only that history and
+                    # write to shm.
+                    if s_diff > 0:
+                        assert last_tsdb_dt > start_dt
+                        selected = array['time'] > last_tsdb_dt.timestamp()
+                        to_push = array[selected]
+                        log.info(
+                            f'Pushing partial frame {to_push.size} to shm'
+                        )
+                        return to_push
+
+                    else:
+                        return array
+
                 # start history anal and load missing new data via backend.
                 async with open_history_client(fqsn) as hist:
 
                     # get latest query's worth of history all the way
                     # back to what is recorded in the tsdb
                     array, start_dt, end_dt = await hist(end_dt='')
-                    shm.push(array)
+                    to_push = diff_history(array, start_dt, end_dt)
+                    shm.push(to_push)
 
                     # let caller unblock and deliver latest history frame
                     task_status.started(shm)
@@ -291,33 +317,13 @@ async def manage_history(
                     # pull new history frames until we hit latest
                     # already in the tsdb
                     while start_dt > last_tsdb_dt:
-
                         array, start_dt, end_dt = await hist(end_dt=start_dt)
-                        s_diff = (last_tsdb_dt - start_dt).seconds
-
-                        # if we detect a partial frame's worth of data
-                        # that is new, slice out only that history and
-                        # write to shm.
-                        if s_diff > 0:
-                            assert last_tsdb_dt > start_dt
-                            selected = array['time'] > last_tsdb_dt.timestamp()
-                            to_push = array[selected]
-                            log.info(
-                                f'Pushing partial frame {to_push.size} to shm'
-                            )
-                            shm.push(to_push, prepend=True)
-                            break
-
-                        else:
-                            # write to shm
-                            log.info(f'Pushing {array.size} datums to shm')
-                            shm.push(array, prepend=True)
+                        to_push = diff_history(array, start_dt, end_dt)
+                        shm.push(to_push, prepend=True)
 
                     # TODO: see if there's faster multi-field reads:
                     # https://numpy.org/doc/stable/user/basics.rec.html#accessing-multiple-fields
                     # re-index  with a `time` and index field
-                    # await tractor.breakpoint()
-
                     shm.push(
                         fastest[-shm._first.value:],