Segfetcher: Make NextQuery dependent on segments

[oncilla]

With this PR, the next query is dependent on the verified segments.
The next query interval is at least minQueryInterval and at most
the configured query interval.

However, if only segments are found where the time until segment
expiration minus the expirationLeadTime (2 minutes) are found that are
less than the configured query interval, then that is chosen.

I.e. the query interval is:

maxExpirationDiff = max(seg.Exp().Add(-expirationLeadTime).Sub(now))
min(max(minQueryInterval, maxExpirationDiff), QueryInterval)

fixes #2979

Also, revert band-aid fix introduced by #3089

This change is 

[scrye]

---

go/lib/infra/modules/segfetcher/fetcher.go, line 198 at r1 (raw file):

// nextQuery decides the next time a query should be issued based on the
// received segments.
func (f *Fetcher) nextQuery(segs []*seghandler.SegWithHP) time.Time {

Maybe simplify this a bit:

lastExpiration := getLastExpiration(segs)
lastExpiration -= expirationLeadTime
relativeNextQuery := findNearestInInterval(lastExpiration, minQueryInterval, f.QueryInterval)
return time.Now() + relativeNextQuery

Better names probably exist.

[oncilla]

Reviewable status: 0 of 5 files reviewed, 1 unresolved discussion (waiting on @scrye)

---

go/lib/infra/modules/segfetcher/fetcher.go, line 198 at r1 (raw file):

Previously, scrye (Sergiu Costea) wrote…

Maybe simplify this a bit:

lastExpiration := getLastExpiration(segs)
lastExpiration -= expirationLeadTime
relativeNextQuery := findNearestInInterval(lastExpiration, minQueryInterval, f.QueryInterval)
return time.Now() + relativeNextQuery

Better names probably exist.

Done.

[scrye]

Reviewed 5 of 5 files at r1, 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved