Improved documentation.

main.go

@@ -14,9 +14,34 @@ import (
 )
 
 // Payload struct
-// Dt1, Dt2, Rt1, Rt2 and G are meter readings
+//
+// All metrics are stored in PostgreSQL as INT and not NUMERIC or FLOAT to optimise their storage size.
+//
+// Dt1, Dt2, Rt1, Rt2 and G are cumulative meter readings.
 // 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.
+//   Storage for non-NULL values every second:
+//     86,400 entries/day×4 bytes/entry=345,600 bytes/day86,400entries/day×4bytes/entry=345,600bytes/day
+//   Storage for non-NULL values every minute:
+//     1,440 entries/day×4 bytes/entry=5,760 bytes/day1,440entries/day×4bytes/entry=5,760bytes/day
+//   Storage savings:
+//     345,600 bytes/day−5,760 bytes/day=339,840 bytes/day345,600bytes/day−5,760bytes/day=339,840bytes/day
+//     (about 331.5 KB / day or 9.72 MB / month)
+//   In practice, savings will be even higher when gas is not being consumed continuously.
+//
+// When Tariff 1 is active, Tariff 2 isn't.
+//   Therefore, only updating their values on-change should at least half their 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, so should be doubled.
+//     10.52 * 2 = 21.04 MB.
+//   In practice, savings will be even higher when electricity is not being consumed continuously.
+
 type Payload struct {
 	T   string `json:"t"`   // Timestamp
 	Dt1 *int   `json:"dt1"` // Delivered / imported meter reading tariff 1 (kWh)