How best to support different underlying value storage models?

[ideasasylum]

In the simplest case, counter values are just integers.

• But then what if you wanted to count really large numbers. BigInt?
• We needed to count percentages (calculated from other counters) such as spam rate. So Float? Or Double? Or even Decimal?
• We will need to store counters as HLL values enabling us to approximately count unique values
• We may want to support slotted counters to allow higher concurrent writes without locking
• We will need to support counters over time, i.e., number of emails sent per month
• We might want to support counters/events in external systems like Redis

It's hard to support these different representations in a single database table. We could make Counter::Value an STI table but then we'd be storing Integer, Float, HLL, and maybe JSONB columns for each counter.But maybe that's fine if those columns are nil since they only require ~1bit of storage??

Alternatively, the counter should write to different tables depending on the configuration?

…which gets be reconsidering having separate counter definitions. Perhaps values should just be Rails models? e.g.

# This will be stored on the counter_values table with an type value of "MyCounter" (i.e., using STI)
class MyCounter < Counter::Value
  # Some configuration methods to specific what it is counting, conditionals, hooks etc
  count…
end

# This will be stored in the counter_hll table with a type value of "PageVisitsCounter"
class PageVisitsCounter < Counter::HLL
  # some config…
end

Using different tables might make sorting/filtering a little harder but probably doable.