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source/components/history.markdown

@@ -0,0 +1,52 @@
+---
+layout: page
+title: "History support"
+description: "Instructions how enable historyt support for Home Assistant."
+date: 2015-03-23 19:59
+sidebar: false
+comments: false
+sharing: true
+footer: true
+---
+
+This component will track everything that is going on within Home Assistant and allows the user to browse through it.
+
+```yaml
+# Example configuration.yaml entry
+history:
+```
+
+<p class='img'>
+  <a href='{{site_root}}/images/screenshots/component_history_24h.png'>
+    <img src='{{site_root}}/images/screenshots/component_history_24h.png' />
+  </a>
+</p>
+
+<p class='note'>
+Events are saved in a local database. Google Graphs is used to draw the graph. Drawing is happening 100% in your browser - no data is transfered to anyone at any time.
+</p>
+
+### Implementation details
+
+The history is stored in a SQLite databse `home-assistant.db` within your config directory.
+
+ - events table is all events except time_changed that happened while recorder component was running.
+ - states table contains all the new_state values of state_changed events.
+ - Inside the states table you have:
+   - entity_id: the entity_id of the entity
+   - state: the state of the entity
+   - attributes: JSON of the state attributes
+   - last_changed: timestamp last time the state has changed. A state_changed event can happen when just attributes change.
+   - last_updated: timestamp anything has changed (state, attributes)
+   - created: timestamp this entry was inserted into the database
+
+When the history component queries the states table it only selects states where the state has changed: `WHERE last_changed=last_updated`
+
+#### On dates
+
+SQLite databases do not support native dates. That's why all the dates are saved in seconds since the UNIX epoch. Convert them manually using this site or in Python:
+
+```python
+from datetime import datetime
+datetime.fromtimestamp(1422830502)
+```