spread fetch time and omit single errors

Spread fetch time reduces peak load on servers

custom_components/epex_spot/EPEXSpot/EPEXSpotWeb/__init__.py

@@ -130,9 +130,11 @@ async def fetch(self):
         delivery_date = datetime.now(ZoneInfo("Europe/Berlin"))
         # get data for remaining day and upcoming day
         # Data for the upcoming day is typically available at 12:45
-        self._marketdata = await self._fetch_day(delivery_date) + await self._fetch_day(
+        marketdata = await self._fetch_day(delivery_date) + await self._fetch_day(
             delivery_date + timedelta(days=1)
         )
+        # overwrite cached marketdata only on success
+        self._marketdata = marketdata
 
     async def _fetch_day(self, delivery_date):
         data = await self._fetch_data(delivery_date)

custom_components/epex_spot/__init__.py

@@ -1,6 +1,8 @@
 """Component for EPEX Spot support."""
 import logging
 from typing import Callable, Any
+import asyncio
+import random
 
 import homeassistant.helpers.config_validation as cv
 import voluptuous as vol
@@ -105,7 +107,9 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
         )
 
     entry.async_on_unload(
-        async_track_time_change(hass, source.fetch, hour=None, minute=58, second=0)
+        async_track_time_change(
+            hass, coordinator.fetch_source, hour=None, minute=50, second=0
+        )
     )
 
     # service call handling
@@ -211,6 +215,17 @@ async def _async_update_data(self) -> dict[str, Any]:
     async def on_refresh(self, *args: Any):
         await self.async_refresh()
 
+    async def fetch_source(self, *args: Any):
+        # spread fetch over 9 minutes to reduce peak load on servers
+        await asyncio.sleep(random.uniform(0, 9 * 60))
+        try:
+            await self.source.fetch()
+            self._error_count = 0
+        except Exception:  # pylint: disable=broad-except
+            self._error_count += 1
+            if self._error_count >= 3:
+                raise
+
 
 class EpexSpotEntity(CoordinatorEntity, Entity):
     """A entity implementation for EPEX Spot service."""