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replication/driver: simplify second-attempt step correlation code & fix statekeeping

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Before this change, the step correlation code returned early in several cases:
- did not set f.planning.done in the cases where it was a no-op
- did not set f.planning.err in the cases where correlation did not
  succeed

Reported-by: InsanePrawn <insane.prawny@gmail.com>
This commit is contained in:
Christian Schwarz 2021-01-13 21:35:49 +01:00
parent 96d5288667
commit 967263dffa
1 changed files with 24 additions and 44 deletions
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70
replication/driver/replication_driver.go
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@ -492,57 +492,37 @@ func (f *fs) do(ctx context.Context, pq *stepQueue, prev *fs) {
// => don't set f.planning.done just yet
f.debug("initial len(fs.planned.steps) = %d", len(f.planned.steps))
// for not-first attempts, only allow fs.planned.steps
// up to including the originally planned target snapshot
// for not-first attempts that succeeded in planning, only allow fs.planned.steps
// up to and including the originally planned target snapshot
if prev != nil && prev.planning.done && prev.planning.err == nil {
f.debug("attempting to correlate plan with previous attempt to find out what is left to do")
// find the highest of the previously uncompleted steps for which we can also find a step
// in our current plan
prevUncompleted := prev.planned.steps[prev.planned.step:]
if len(prevUncompleted) == 0 {
f.debug("prevUncompleted is empty")
var target struct{ prev, cur int }
target.prev = -1
target.cur = -1
out:
for p := len(prevUncompleted) - 1; p >= 0; p-- {
for q := len(f.planned.steps) - 1; q >= 0; q-- {
if prevUncompleted[p].step.TargetEquals(f.planned.steps[q].step) {
target.prev = p
target.cur = q
break out
}
}
}
if target.prev == -1 || target.cur == -1 {
f.debug("no correlation possible between previous attempt and this attempt's plan")
f.planning.err = newTimedError(fmt.Errorf("cannot correlate previously failed attempt to current plan"), time.Now())
return
}
if len(f.planned.steps) == 0 {
f.debug("fs.planned.steps is empty")
return
}
prevFailed := prevUncompleted[0]
curFirst := f.planned.steps[0]
// we assume that PlanFS retries prevFailed (using curFirst)
if !prevFailed.step.TargetEquals(curFirst.step) {
f.debug("Targets don't match")
// Two options:
// A: planning algorithm is broken
// B: manual user intervention inbetween
// Neither way will we make progress, so let's error out
stepFmt := func(step *step) string {
r := step.report()
s := r.Info
if r.IsIncremental() {
return fmt.Sprintf("%s=>%s", s.From, s.To)
f.planned.steps = f.planned.steps[0:target.cur]
f.debug("found correlation, new steps are len(fs.planned.steps) = %d", len(f.planned.steps))
} else {
return fmt.Sprintf("full=>%s", s.To)
f.debug("previous attempt does not exist or did not finish planning, no correlation possible, taking this attempt's plan as is")
}
}
msg := fmt.Sprintf("last attempt's uncompleted step %s does not correspond to this attempt's first planned step %s",
stepFmt(prevFailed), stepFmt(curFirst))
f.planned.stepErr = newTimedError(errors.New(msg), time.Now())
return
}
// only allow until step targets diverge
min := len(prevUncompleted)
if min > len(f.planned.steps) {
min = len(f.planned.steps)
}
diverge := 0
for ; diverge < min; diverge++ {
f.debug("diverge compare iteration %d", diverge)
if !f.planned.steps[diverge].step.TargetEquals(prevUncompleted[diverge].step) {
break
}
}
f.debug("diverge is %d", diverge)
f.planned.steps = f.planned.steps[0:diverge]
}
f.debug("post-prev-merge len(fs.planned.steps) = %d", len(f.planned.steps))
// now we are done planning (f.planned.steps won't change from now on)
f.planning.done = true