Golang Key.Less方法代碼示例

// getDescriptors looks up the range descriptor to use for a query over the
// key range [from,to), with the given lookupOptions. The range descriptor
// which contains the range in which the request should start its query is
// returned first; the returned bool is true in case the given range reaches
// outside the first descriptor.
// In case either of the descriptors is discovered stale, the returned closure
// should be called; it evicts the cache appropriately.
// Note that `from` and `to` are not necessarily Key and EndKey from a
// RequestHeader; it's assumed that they've been translated to key addresses
// already (via KeyAddress).
func (ds *DistSender) getDescriptors(from, to proto.Key, options lookupOptions) (*proto.RangeDescriptor, bool, func(), error) {
	var desc *proto.RangeDescriptor
	var err error
	var descKey proto.Key
	if !options.useReverseScan {
		descKey = from
	} else {
		descKey = to
	}
	desc, err = ds.rangeCache.LookupRangeDescriptor(descKey, options)

	if err != nil {
		return nil, false, nil, err
	}

	// Checks whether need to get next range descriptor. If so, returns true.
	needAnother := func(desc *proto.RangeDescriptor, isReverse bool) bool {
		if isReverse {
			return from.Less(desc.StartKey)
		}
		return desc.EndKey.Less(to)
	}

	evict := func() {
		ds.rangeCache.EvictCachedRangeDescriptor(descKey, desc, options.useReverseScan)
	}

	return desc, needAnother(desc, options.useReverseScan), evict, nil
}

// prev gives the right boundary of the union of all requests which don't
// affect keys larger than the given key.
// TODO(tschottdorf): again, better on BatchRequest itself, but can't pull
// 'keys' into 'proto'.
func prev(ba proto.BatchRequest, k proto.Key) proto.Key {
	candidate := proto.KeyMin
	for _, union := range ba.Requests {
		h := union.GetValue().(proto.Request).Header()
		addr := keys.KeyAddress(h.Key)
		eAddr := keys.KeyAddress(h.EndKey)
		if len(eAddr) == 0 {
			// Can probably avoid having to compute Next() here if
			// we're in the mood for some more complexity.
			eAddr = addr.Next()
		}
		if !eAddr.Less(k) {
			if !k.Less(addr) {
				// Range contains k, so won't be able to go lower.
				return k
			}
			// Range is disjoint from [KeyMin,k).
			continue
		}
		// We want the largest surviving candidate.
		if candidate.Less(addr) {
			candidate = addr
		}
	}
	return candidate
}

// clearOverlappingCachedRangeDescriptors looks up and clears any
// cache entries which overlap the specified key or descriptor.
func (rdc *rangeDescriptorCache) clearOverlappingCachedRangeDescriptors(key, metaKey proto.Key, desc *proto.RangeDescriptor) {
	if desc.StartKey.Equal(desc.EndKey) { // True for some unittests.
		return
	}
	// Clear out any descriptors which subsume the key which we're going
	// to cache. For example, if an existing KeyMin->KeyMax descriptor
	// should be cleared out in favor of a KeyMin->"m" descriptor.
	k, v, ok := rdc.rangeCache.Ceil(rangeCacheKey(metaKey))
	if ok {
		descriptor := v.(*proto.RangeDescriptor)
		if !key.Less(descriptor.StartKey) && !descriptor.EndKey.Less(key) {
			if log.V(1) {
				log.Infof("clearing overlapping descriptor: key=%s desc=%s", k, descriptor)
			}
			rdc.rangeCache.Del(k.(rangeCacheKey))
		}
	}
	// Also clear any descriptors which are subsumed by the one we're
	// going to cache. This could happen on a merge (and also happens
	// when there's a lot of concurrency). Iterate from the range meta key
	// after RangeMetaKey(desc.StartKey) to the range meta key for desc.EndKey.
	rdc.rangeCache.DoRange(func(k, v interface{}) {
		if log.V(1) {
			log.Infof("clearing subsumed descriptor: key=%s desc=%s", k, v.(*proto.RangeDescriptor))
		}
		rdc.rangeCache.Del(k.(rangeCacheKey))
	}, rangeCacheKey(keys.RangeMetaKey(desc.StartKey).Next()),
		rangeCacheKey(keys.RangeMetaKey(desc.EndKey)))
}

// ComputeSplitKeys takes a start and end key and returns an array of keys
// at which to split the span [start, end).
// The only required splits are at each user table prefix.
func (s *SystemConfig) ComputeSplitKeys(startKey, endKey proto.Key) []proto.Key {
	if TestingDisableTableSplits {
		return nil
	}

	tableStart := proto.Key(keys.UserTableDataMin)
	if !tableStart.Less(endKey) {
		// This range is before the user tables span: no required splits.
		return nil
	}

	startID, ok := ObjectIDForKey(startKey)
	if !ok || startID <= keys.MaxReservedDescID {
		// The start key is either:
		// - not part of the structured data span
		// - part of the system span
		// In either case, start looking for splits at the first ID usable
		// by the user data span.
		startID = keys.MaxReservedDescID + 1
	} else {
		// The start key is either already a split key, or after the split
		// key for its ID. We can skip straight to the next one.
		startID++
	}

	// Find the largest object ID.
	// We can't keep splitting until we reach endKey as it could be proto.KeyMax.
	endID, err := s.GetLargestObjectID()
	if err != nil {
		log.Errorf("unable to determine largest object ID from system config: %s", err)
		return nil
	}

	// Build key prefixes for sequential table IDs until we reach endKey.
	var splitKeys proto.KeySlice
	var key proto.Key
	// endID could be smaller than startID if we don't have user tables.
	for id := startID; id <= endID; id++ {
		key = keys.MakeTablePrefix(id)
		// Skip if the range starts on a split key.
		if !startKey.Less(key) {
			continue
		}
		// Handle the case where EndKey is already a table prefix.
		if !key.Less(endKey) {
			break
		}
		splitKeys = append(splitKeys, key)
	}

	return splitKeys
}

// verifyBinarySearchTree checks to ensure that all keys to the left of the root
// node are less than it, and all nodes to the right of the root node are
// greater than it. It recursively walks the tree to perform this same check.
func verifyBinarySearchTree(t *testing.T, nodes map[string]proto.RangeTreeNode, testName string, node *proto.RangeTreeNode, keyMin, keyMax proto.Key) {
	if node == nil {
		return
	}
	if !node.Key.Less(keyMax) {
		t.Errorf("%s: Failed Property BST - The key %s is not less than %s.", testName, node.Key, keyMax)
	}
	// We need the extra check since proto.KeyMin is actually a range start key.
	if !keyMin.Less(node.Key) && !node.Key.Equal(proto.KeyMin) {
		t.Errorf("%s: Failed Property BST - The key %s is not greater than %s.", testName, node.Key, keyMin)
	}
	left, right := getLeftAndRight(t, nodes, testName, node)
	verifyBinarySearchTree(t, nodes, testName, left, keyMin, node.Key)
	verifyBinarySearchTree(t, nodes, testName, right, node.Key, keyMax)
}

// next gives the left boundary of the union of all requests which don't
// affect keys less than the given key.
// TODO(tschottdorf): again, better on BatchRequest itself, but can't pull
// 'keys' into 'proto'.
func next(ba proto.BatchRequest, k proto.Key) proto.Key {
	candidate := proto.KeyMax
	for _, union := range ba.Requests {
		h := union.GetValue().(proto.Request).Header()
		addr := keys.KeyAddress(h.Key)
		if addr.Less(k) {
			if eAddr := keys.KeyAddress(h.EndKey); k.Less(eAddr) {
				// Starts below k, but continues beyond. Need to stay at k.
				return k
			}
			// Affects only [KeyMin,k).
			continue
		}
		// We want the smallest of the surviving candidates.
		if addr.Less(candidate) {
			candidate = addr
		}
	}
	return candidate
}

// insert performs the insertion of a new range into the RangeTree. It will
// recursively call insert until it finds the correct location. It will not
// overwrite an already existing key, but that case should not occur.
func (tc *treeContext) insert(node *proto.RangeTreeNode, key proto.Key) (*proto.RangeTreeNode, error) {
	if node == nil {
		// Insert the new node here.
		node = &proto.RangeTreeNode{
			Key: key,
		}
		tc.setNode(node)
	} else if key.Less(node.Key) {
		// Walk down the tree to the left.
		left, err := tc.getNode(node.LeftKey)
		if err != nil {
			return nil, err
		}
		left, err = tc.insert(left, key)
		if err != nil {
			return nil, err
		}
		if node.LeftKey == nil || !(*node.LeftKey).Equal(left.Key) {
			node.LeftKey = &left.Key
			tc.setNode(node)
		}
	} else {
		// Walk down the tree to the right.
		right, err := tc.getNode(node.RightKey)
		if err != nil {
			return nil, err
		}
		right, err = tc.insert(right, key)
		if err != nil {
			return nil, err
		}
		if node.RightKey == nil || !(*node.RightKey).Equal(right.Key) {
			node.RightKey = &right.Key
			tc.setNode(node)
		}
	}
	return tc.walkUpRot23(node)
}

// verifyBinarySearchTree checks to ensure that all keys to the left of the root
// node are less than it, and all nodes to the right of the root node are
// greater than it. It recursively walks the tree to perform this same check.
func verifyBinarySearchTree(t *testing.T, tc *treeContext, testName string, node *proto.RangeTreeNode, keyMin, keyMax proto.Key) {
	if !node.Key.Less(keyMax) {
		t.Errorf("%s: Failed Property BST - The key %s is not less than %s.", testName, node.Key, keyMax)
	}
	if !keyMin.Less(node.Key) {
		t.Errorf("%s: Failed Property BST - The key %s is not greater than %s.", testName, node.Key, keyMin)
	}

	if node.LeftKey != nil {
		left, err := tc.getNode(node.LeftKey)
		if err != nil {
			t.Fatal(err)
		}
		verifyBinarySearchTree(t, tc, testName, left, keyMin, node.Key)
	}
	if node.RightKey != nil {
		right, err := tc.getNode(node.RightKey)
		if err != nil {
			t.Fatal(err)
		}
		verifyBinarySearchTree(t, tc, testName, right, node.Key, keyMax)
	}
}