Reasonable query search depth

[ggwpez]

Location: [backend/eth] All queries where past events are read, namely:

• Adjudicator.ensureConcluded: searches for ChannelUpdate events
• Adjudicator.ensureWithdrawn: searches for Withdrawn events
• Adjudicator.Subscribe: searches for ChannelUpdate events
• Funder.checkFunded: searches for Deposited events
• Funder.waitforFundingConfirmation: searches for Deposited events

Current situation:
When creating filter queries for events, a startBlockOffset value is needed which defines how many blocks into the past a query should go.
We currently use the constant startBlockOffset=100 for all queries.

Problem: I dont remember how this value was chosen or if it was tested in any way.
We need either one global or one per query startBlockOffset value that is reasonable.
Maybe some research must be done on how to chose this.

Having this would be important for our mainnet release.

[matthiasgeihs]

We should consider using a logic where the caller can specify a time until which to go back. Then the subscription would start at the first block after the specified point in time.

For example, we may know that we only agreed to open a channel at time t, then we only need to listen for events on that channel for t'>=t.

[ggwpez]

For example, we may know that we only agreed to open a channel at time t, then we only need to listen for events on that channel for t'>=t.

We could do some kind of Selector or Predicate type which has multiple constructors; eg. SinceBlockTime, SinceBlockNum or SincePastBlocks(n) (which would query n blocks into the past).
What do you think @matthiasgeihs ?