private async Task PushQueueAsync(IFdbTransaction tr, IDynamicKeySubspace queue, Slice taskId)
{
//TODO: use a high contention algo ?
// - must support Push and Pop
// - an empty queue must correspond to an empty subspace
// get the current size of the queue
var range = queue.ToRange();
var lastKey = await tr.Snapshot.GetKeyAsync(KeySelector.LastLessThan(range.End)).ConfigureAwait(false);
int count = lastKey < range.Begin ? 0 : queue.DecodeFirst <int>(lastKey) + 1;
// set the value
tr.Set(queue.Encode(count, GetRandomId()), taskId);
}
private async Task <KeyValuePair <Slice, Slice> > FindRandomItem(IFdbTransaction tr, IDynamicKeySubspace ring)
{
var range = ring.ToRange();
// start from a random position around the ring
var key = ring.Encode(GetRandomId());
// We want to find the next item in the clockwise direction. If we reach the end of the ring, we "wrap around" by starting again from the start
// => So we do find_next(key <= x < MAX) and if that does not produce any result, we do a find_next(MIN <= x < key)
// When the ring only contains a few items (or is empty), there is more than 50% change that we wont find anything in the first read.
// To reduce the latency for this case, we will issue both range reads at the same time, and discard the second one if the first returned something.
// This should reduce the latency in half when the ring is empty, or when it contains only items before the random key.
var candidate = await tr.GetRange(key, range.End).FirstOrDefaultAsync();
if (!candidate.Key.IsPresent)
{
candidate = await tr.GetRange(range.Begin, key).FirstOrDefaultAsync();
}
return(candidate);
}
KeyRange IKeySubspace.ToRange()
{
return(m_globalSpace.ToRange());
}