Method _reserveSequenceBatch

db/sequence_allocator.go:344–380

Reserve a new sequence range, based on batch size. Called by nextSequence when the previously allocated sequences have all been used.

(ctx context.Context)

// Reserve a new sequence range, based on batch size.  Called by nextSequence when the previously allocated sequences have all been used.
func (s *sequenceAllocator) _reserveSequenceBatch(ctx context.Context) error {

	// If the time elapsed since the last reserveSequenceRange invocation reserve is shorter than our target frequency,
	// this indicates we're making an incr call more frequently than we want to.  Triggers an increase in batch size to
	// reduce incr frequency.
	if time.Since(s.lastSequenceReserveTime) < MaxSequenceIncrFrequency {
		s.sequenceBatchSize = s.sequenceBatchSize * sequenceBatchMultiplier
		if s.sequenceBatchSize > maxBatchSize {
			s.sequenceBatchSize = maxBatchSize
		}
		base.DebugfCtx(ctx, base.KeyCRUD, "Increased sequence batch to %d", s.sequenceBatchSize)
	}

	max, err := s._incrementSequence(s.sequenceBatchSize)
	if err != nil {
		base.WarnfCtx(ctx, "Error from incrementSequence in _reserveSequences(%d): %v", s.sequenceBatchSize, err)
		return err
	}

	// check for rollback of _sync:seq document
	minimumExpectedValue := s.max + s.sequenceBatchSize
	if max < minimumExpectedValue {
		// rollback of _sync:seq detected
		max, err = s._fixSyncSeqRollback(ctx, max, minimumExpectedValue)
		if err != nil {
			return err
		}
	}

	// Update max and last used sequences.  Last is updated here to account for sequences allocated/used by other
	// Sync Gateway nodes
	s.max = max
	s.last = max - s.sequenceBatchSize
	s.lastSequenceReserveTime = time.Now()

	return nil
}

// Gets the _sync:seq document value.  Retry handling provided by bucket.Get.
func (s *sequenceAllocator) getSequence() (max uint64, err error) {