diff --git a/piker/data/cli.py b/piker/data/cli.py
index 5b9c854d..6ea2503d 100644
--- a/piker/data/cli.py
+++ b/piker/data/cli.py
@@ -119,14 +119,14 @@ def ms_shell(config, tl, host, port):
     Start an IPython shell ready to query the local marketstore db.
 
     '''
-    from piker.data.marketstore import backfill_history
+    from piker.data.marketstore import backfill_history_diff
     from piker._daemon import open_piker_runtime
     async def main():
         async with open_piker_runtime(
             'ms_shell',
             enable_modules=['piker.data._ahab'],
         ):
-            await backfill_history()
+            await backfill_history_diff()
             # TODO: write magics to query marketstore
             # from IPython import embed
             # embed()
diff --git a/piker/data/marketstore.py b/piker/data/marketstore.py
index 457f37d7..cdcaeb02 100644
--- a/piker/data/marketstore.py
+++ b/piker/data/marketstore.py
@@ -113,7 +113,7 @@ def mk_tbk(keys: tuple[str, str, str]) -> str:
         ``('SPY', '1Sec', 'TICK')`` -> ``"SPY/1Sec/TICK"```
 
     '''
-    return '{}/' + '/'.join(keys)
+    return '/'.join(keys)
 
 
 def quote_to_marketstore_structarray(
@@ -184,8 +184,8 @@ async def get_client(
         yield client
 
 
-# class MarketStoreError(Exception):
-#     "Generic marketstore client error"
+class MarketStoreError(Exception):
+    "Generic marketstore client error"
 
 
 # def err_on_resp(response: dict) -> None:
@@ -210,13 +210,16 @@ tf_in_1s = bidict({
 })
 
 
-# @acm
-async def load_history(
-    symbol: Symbol,
+async def manage_history(
+    fqsn: str,
     period: int = 1,  # in seconds
 
-) -> np.ndarray:
+) -> dict[str, np.ndarray]:
+    '''
+    Load a series by key and deliver in ``numpy`` struct array
+    format.
 
+    '''
     async with get_client() as client:
 
         tfstr = tf_in_1s[period]
@@ -225,16 +228,17 @@ async def load_history(
         )
         # Dig out `numpy` results map
         arrays = {}
-        await tractor.breakpoint()
         # for qr in [onem, fivem]:
-        #     for name, data_set in qr.by_symbols().items():
-        #         arrays[(name, qr)] = data_set.array
+        for name, data_set in result.by_symbols().items():
+            arrays[(name, qr)] = data_set.array
 
+        await tractor.breakpoint()
         # # TODO: backfiller loop
         # array = arrays[(fqsn, qr)]
+        return arrays
 
 
-async def backfill_history(
+async def backfill_history_diff(
     # symbol: Symbol
 
 ) -> list[str]:
@@ -251,7 +255,6 @@ async def backfill_history(
 
     fqsn = mk_fqsn(broker, symbol)
 
-    print('yo')
     async with (
         get_client() as client,
         maybe_open_feed(
@@ -263,21 +266,52 @@ async def backfill_history(
 
         ) as (feed, stream),
     ):
-        print('yo')
-        ohlcv = feed.shm.array
-        mkts_dt = np.dtype(_ohlcv_dt)
-
-        print('yo')
         syms = await client.list_symbols()
         log.info(f'Existing symbol set:\n{pformat(syms)}')
 
-        # build mkts schema compat array
+        # diff db history with shm and only write the missing portions
+        ohlcv = feed.shm.array
+
+        key = (fqsn, '1Sec', 'OHLCV')
+        tbk = mk_tbk(key)
+
+        # diff vs. existing array and append new history
+        # TODO:
+
+        # TODO: should be no error?
+        # assert not resp.responses
+
+        start = time.time()
+
+        qr = await client.query(
+            # Params(fqsn, '1Sec`', 'OHLCV',)
+            Params(*key),
+        )
+        # # Dig out `numpy` results map
+        arrays: dict[tuple[str, int], np.ndarray] = {}
+        for name, data_set in qr.by_symbols().items():
+            in_secs = tf_in_1s.inverse[data_set.timeframe]
+            arrays[(name, in_secs)] = data_set.array
+
+        s1 = arrays[(fqsn, 1)]
+        to_append = ohlcv[ohlcv['time'] > s1['Epoch'][-1]]
+
+        end_diff = time.time()
+        diff_ms = round((end_diff - start) * 1e3, ndigits=2)
+
+        log.info(
+            f'Appending {to_append.size} datums to tsdb from shm\n'
+            f'Total diff time: {diff_ms} ms'
+        )
+
+        # build mkts schema compat array for writing
+        mkts_dt = np.dtype(_ohlcv_dt)
         mkts_array = np.zeros(
-            len(ohlcv),
+            len(to_append),
             dtype=mkts_dt,
         )
         # copy from shm array
-        mkts_array[:] = ohlcv[[
+        mkts_array[:] = to_append[[
             'time',
             'open',
             'high',
@@ -286,39 +320,27 @@ async def backfill_history(
             'volume',
         ]]
 
-        key = (fqsn, '1Sec', 'OHLCV')
-        tbk = mk_tbk(key)
-
-        # diff vs. existing array and append new history
-        # TODO:
-
         # write to db
         resp = await client.write(
             mkts_array,
             tbk=tbk,
             # NOTE: will will append duplicates
             # for the same timestamp-index.
-            # isvariablelength=True,
+            isvariablelength=True,
         )
-        # TODO: should be no error?
-        # assert not resp.responses
-
-        # # Dig out `numpy` results map
-        qr = await client.query(
-            Params(fqsn, '1Min`', 'OHLCV',)
+        end_write = time.time()
+        diff_ms = round((end_write - end_diff) * 1e3, ndigits=2)
+        log.info(
+            f'Wrote {to_append.size} datums to tsdb\n'
+            f'Total write time: {diff_ms} ms'
         )
-        qr = await client.query(
-            # Params(fqsn, '1Sec`', 'OHLCV',)
-            Params(*key),
-        )
-        arrays = {}
-        # for qr in [onem, fivem]:
-        for name, data_set in qr.by_symbols().items():
-            arrays[(name, qr)] = data_set.array
+        for resp in resp.responses:
+            err = resp.error
+            if err:
+                raise MarketStoreError(err)
 
         # TODO: backfiller loop
-        array = arrays[(fqsn, qr)]
-        await tractor.breakpoint()
+        # await tractor.breakpoint()
 
 
 async def ingest_quote_stream(