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README.md

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+# P1 logger
+
+P1 logger is a tool designed to store meter data conforming to the [ESMR or DSMR (European / Dutch Smart Meter Requirements) standard](https://github.com/jvhaarst/DSMR-P1-telegram-reader/blob/master/documentation/Dutch%20Smart%20Meter%20Requirements%20v5.0.2%20Final%20P1.pdf) as efficiently as possible in a PostgreSQL database.
+
+To store the data as efficiently as possible, a few design choices had to be made.
+
+All metrics are stored as INT and not NUMERIC or FLOAT to optimise their storage size.
+
+Dt1, Dt2, Rt1, Rt2, G, F and Fl are cumulative meter readings. Therefore, they function as counters that can only go up. By making them pointers to int, they can be set to 'nil' when the reading has not changed. This way, they are logged as NULL in the database when no change has happened, saving storage capacity. As an added benefit, this also make data retrieval, visualisation and analysis more light-weight.
+
+Gas consumption is updated once per minute. Not saving intermittent values theoretically saves 4 bytes per value. An average month has 43 829.0639 minutes.
+4*43829,0639 = 175,316.26 bytes = 0.18 MB
+
+In practice, storage will be even lower when gas is not being consumed continuously, as a new metric won't be available for every minute.
+
+When Tariff 1 is active, Tariff 2 isn't. When energy is being imported, it is not being returned.
+
+Therefore, only updating their values on-change should save at least 75% storage capacity requirements
+An average month has 2 629 743.83 seconds.
+
+This saves at least:
+2,629,743.83 seconds * 4 bytes = 10,518,975.32 bytes = 10,518.98 kB = 10.52 MB
+This applies both to Dt1 and Dt2 as well as Rt1 and Rt2, only one is recorded at a time.
+10.52 * 3 = 31.56 MB.
+
+In addition, many meters only update these metrics once every 10 seconds, meaning even more storage capacity is saved:
+10.52 / 10 * 9 = 9,468 MB.
+
+For D1-3 and R1-3, either Dx or Rx will be active. Therefore, their storage requirements can be sliced in half, saving 3 * 10.52 = 42.08 MB. This is different for D and R, as these contain the sum of each phase and are reported simultaneously. Not saving failures when there is no change, will save around 10.52MB per month per metric, so an additional 21.04MB. Theoretical storage requirements for a DSMR5 meter with metrics emitted every second:
+
+Column				Column size (bytes)		Per month (MB)	X	Total (MB)
+---------------------------------------------------------------------------
+Timestamp			8 bytes					021.04
+Dt1, Dt2, Rt1, Rt2	4 bytes					001.05
+D, R					4 bytes					010.52
+R					4 bytes					010.52
+F					4 bytes					000.00
+Fl					4 bytes					000.00
+G					4 bytes					000.18
+V1-3, C1-3			4 bytes					010.52			6	063.12
+D1-3, R1-3			4 bytes					010.52			3	031.56
+---------------------------------------------------------------------------
+Total															137.99
+
+Compared to no optimisations:
+
+Column				Column size (bytes)		Per month (MB)	X	Total (MB)
+---------------------------------------------------------------------------
+Timestamps 			8 bytes					21.04
+Values				4 bytes					10.52			21	220.92
+---------------------------------------------------------------------------
+Total															241.96
+
+Conclusion:
+At the expense of having to create more complicated queries for analysis and visualisation, the optimisations save at least 103.97 MB or 1-137.99/241.96 = 43% in uncompressed storage space per month.
+
+### Columns
+
+- timestamp
+- delivered_tariff1, delivered_tariff2, returned_tariff1, returned_tariff2
+- delivery_all
+- returning_all
+- failures
+- long_failures
+- gas
+- voltage_l1, voltage_l2, voltage_l3
+- current_l1, current_l2, current_l3
+- delivery_l1, delivery_l2, delivery_l3
+- returning_l1, returning_l2, returning_l3