Golang Key.Next方法代碼示例

// getCachedRangeDescriptorLocked is a helper function to retrieve the
// descriptor of the range which contains the given key, if present in the
// cache. It is assumed that the caller holds a read lock on rdc.rangeCacheMu.
func (rdc *rangeDescriptorCache) getCachedRangeDescriptorLocked(key proto.Key, inclusive bool) (
	rangeCacheKey, *proto.RangeDescriptor) {
	// The cache is indexed using the end-key of the range, but the
	// end-key is non-inclusive by default.
	var metaKey proto.Key
	if !inclusive {
		metaKey = keys.RangeMetaKey(key.Next())
	} else {
		metaKey = keys.RangeMetaKey(key)
	}

	k, v, ok := rdc.rangeCache.Ceil(rangeCacheKey(metaKey))
	if !ok {
		return nil, nil
	}
	metaEndKey := k.(rangeCacheKey)
	rd := v.(*proto.RangeDescriptor)

	// Check that key actually belongs to the range.
	if !rd.ContainsKey(key) {
		// The key is the EndKey and we're inclusive, so just return the range descriptor.
		if inclusive && key.Equal(rd.EndKey) {
			return metaEndKey, rd
		}
		return nil, nil
	}

	// The key is the StartKey, but we're inclusive and thus need to return the
	// previous range descriptor, but it is not in the cache yet.
	if inclusive && key.Equal(rd.StartKey) {
		return nil, nil
	}
	return metaEndKey, rd
}

// Add the specified timestamp to the cache as covering the range of
// keys from start to end. If end is nil, the range covers the start
// key only. txnID is nil for no transaction. readOnly specifies
// whether the command adding this timestamp was read-only or not.
func (tc *TimestampCache) Add(start, end proto.Key, timestamp proto.Timestamp, txnID []byte, readOnly bool) {
	// This gives us a memory-efficient end key if end is empty.
	if len(end) == 0 {
		end = start.Next()
		start = end[:len(start)]
	}
	if tc.latest.Less(timestamp) {
		tc.latest = timestamp
	}
	// Only add to the cache if the timestamp is more recent than the
	// low water mark.
	if tc.lowWater.Less(timestamp) {
		// Check existing, overlapping entries. Remove superseded
		// entries or return without adding this entry if necessary.
		key := tc.cache.NewKey(start, end)
		for _, o := range tc.cache.GetOverlaps(start, end) {
			ce := o.Value.(cacheEntry)
			if ce.readOnly != readOnly {
				continue
			}
			if o.Key.Contains(key) && !ce.timestamp.Less(timestamp) {
				return // don't add this key; there's already a cache entry with >= timestamp.
			} else if key.Contains(o.Key) && !timestamp.Less(ce.timestamp) {
				tc.cache.Del(o.Key) // delete existing key; this cache entry supersedes.
			}
		}
		ce := cacheEntry{timestamp: timestamp, txnID: txnID, readOnly: readOnly}
		tc.cache.Add(key, ce)
	}
}

// Add adds a command to the queue which affects the specified key
// range. If end is empty, it is set to start.Next(), meaning the
// command affects a single key. The returned interface is the key for
// the command queue and must be re-supplied on subsequent invocation
// of Remove().
//
// Add should be invoked after waiting on already-executing,
// overlapping commands via the WaitGroup initialized through
// GetWait().
func (cq *CommandQueue) Add(start, end proto.Key, readOnly bool) interface{} {
	if len(end) == 0 {
		end = start.Next()
	}
	key := cq.cache.NewKey(start, end)
	cq.cache.Add(key, &cmd{readOnly: readOnly})
	return key
}

// MetaScanBounds returns the start and end keys of the range within which the
// desired meta record can be found by means of an engine scan. The given key
// must be a valid RangeMetaKey as defined by ValidateRangeMetaKey.
func MetaScanBounds(key proto.Key) (proto.Key, proto.Key) {
	if key.Equal(proto.KeyMin) {
		// Special case KeyMin: find the first entry in meta1.
		return Meta1Prefix, Meta1Prefix.PrefixEnd()
	}
	if key.Equal(Meta1KeyMax) {
		// Special case Meta1KeyMax: this is the last key in Meta1, we don't want
		// to start at Next().
		return key, Meta1Prefix.PrefixEnd()
	}
	// Otherwise find the first entry greater than the given key in the same meta prefix.
	return key.Next(), proto.Key(key[:len(Meta1Prefix)]).PrefixEnd()
}

// GetWait initializes the supplied wait group with the number of
// executing commands which overlap the specified key range. If end is
// empty, end is set to start.Next(), meaning the command affects a
// single key. The caller should call wg.Wait() to wait for
// confirmation that all gating commands have completed or
// failed. readOnly is true if the requester is a read-only command;
// false for read-write.
func (cq *CommandQueue) GetWait(start, end proto.Key, readOnly bool, wg *sync.WaitGroup) {
	// This gives us a memory-efficient end key if end is empty.
	if len(end) == 0 {
		end = start.Next()
		start = end[:len(start)]
	}
	for _, c := range cq.cache.GetOverlaps(start, end) {
		c := c.Value.(*cmd)
		// Only add to the wait group if one of the commands isn't read-only.
		if !readOnly || !c.readOnly {
			c.pending = append(c.pending, wg)
			wg.Add(1)
		}
	}
}

// MetaReverseScanBounds returns the range [start,end) within which the desired
// meta record can be found by means of a reverse engine scan. The given key
// must be a valid RangeMetaKey as defined by ValidateRangeMetaKey.
func MetaReverseScanBounds(key proto.Key) (proto.Key, proto.Key, error) {
	if key.Equal(proto.KeyMin) || key.Equal(Meta1Prefix) {
		return nil, nil, NewInvalidRangeMetaKeyError("KeyMin and Meta1Prefix can't be used as the key of reverse scan", key)
	}
	if key.Equal(Meta2Prefix) {
		// Special case Meta2Prefix: this is the first key in Meta2, and the scan
		// interval covers all of Meta1.
		return Meta1Prefix, key.Next(), nil
	}
	// Otherwise find the first entry greater than the given key and find the last entry
	// in the same prefix. For MVCCReverseScan the endKey is exclusive, if we want to find
	// the range descriptor the given key specified,we need to set the key.Next() as the
	// MVCCReverseScan`s endKey. For example:
	// If we have ranges ["", "f") and ["f", "z"), then we'll have corresponding meta records
	// at "f" and "z". If you're looking for the meta record for key "f", then you want the
	// second record (exclusive in MVCCReverseScan), hence key.Next() below.
	return key[:len(Meta1Prefix)], key.Next(), nil
}

// GetMax returns the maximum read and write timestamps which overlap
// the interval spanning from start to end. Cached timestamps matching
// the specified txnID are not considered. If no part of the specified
// range is overlapped by timestamps in the cache, the low water
// timestamp is returned for both read and write timestamps.
//
// The txn ID prevents restarts with a pattern like: read("a"),
// write("a"). The read adds a timestamp for "a". Then the write (for
// the same transaction) would get that as the max timestamp and be
// forced to increment it. This allows timestamps from the same txn
// to be ignored.
func (tc *TimestampCache) GetMax(start, end proto.Key, txnID []byte) (proto.Timestamp, proto.Timestamp) {
	if len(end) == 0 {
		end = start.Next()
	}
	maxR := tc.lowWater
	maxW := tc.lowWater
	for _, o := range tc.cache.GetOverlaps(start, end) {
		ce := o.Value.(cacheEntry)
		if ce.txnID == nil || txnID == nil || !proto.TxnIDEqual(txnID, ce.txnID) {
			if ce.readOnly && maxR.Less(ce.timestamp) {
				maxR = ce.timestamp
			} else if !ce.readOnly && maxW.Less(ce.timestamp) {
				maxW = ce.timestamp
			}
		}
	}
	return maxR, maxW
}

// getCachedRangeDescriptorLocked is a helper function to retrieve the
// descriptor of the range which contains the given key, if present in the
// cache. It is assumed that the caller holds a read lock on rdc.rangeCacheMu.
func (rdc *rangeDescriptorCache) getCachedRangeDescriptorLocked(key proto.Key) (
	rangeCacheKey, *proto.RangeDescriptor) {
	// The cache is indexed using the end-key of the range, but the
	// end-key is non-inclusive. If inclusive is false, we access the
	// cache using key.Next().
	metaKey := keys.RangeMetaKey(key.Next())

	k, v, ok := rdc.rangeCache.Ceil(rangeCacheKey(metaKey))
	if !ok {
		return nil, nil
	}
	metaEndKey := k.(rangeCacheKey)
	rd := v.(*proto.RangeDescriptor)

	// Check that key actually belongs to range
	if !rd.ContainsKey(keys.KeyAddress(key)) {
		return nil, nil
	}
	return metaEndKey, rd
}

func (db *testDescriptorDB) getDescriptor(key proto.Key) []proto.RangeDescriptor {
	response := make([]proto.RangeDescriptor, 0, 3)
	for i := 0; i < 3; i++ {
		v := db.data.Ceil(testDescriptorNode{
			&proto.RangeDescriptor{
				EndKey: key.Next(),
			},
		})
		if v == nil {
			break
		}
		response = append(response, *(v.(testDescriptorNode).RangeDescriptor))
		// Break to keep from skidding off the end of the available ranges.
		if response[i].EndKey.Equal(proto.KeyMax) {
			break
		}
		key = proto.Key(response[i].EndKey).Next()
	}
	return response
}

// MetaScanBounds returns the range [start,end) within which the desired meta
// record can be found by means of an engine scan. The given key must be a
// valid RangeMetaKey as defined by validateRangeMetaKey.
func MetaScanBounds(key proto.Key) (proto.Key, proto.Key, error) {
	if err := validateRangeMetaKey(key); err != nil {
		return nil, nil, err
	}

	if key.Equal(Meta2KeyMax) {
		return nil, nil, NewInvalidRangeMetaKeyError("Meta2KeyMax can't be used as the key of scan", key)
	}

	if key.Equal(proto.KeyMin) {
		// Special case KeyMin: find the first entry in meta1.
		return Meta1Prefix, Meta1Prefix.PrefixEnd(), nil
	}
	if key.Equal(Meta1KeyMax) {
		// Special case Meta1KeyMax: this is the last key in Meta1, we don't want
		// to start at Next().
		return key, Meta1Prefix.PrefixEnd(), nil
	}
	// Otherwise find the first entry greater than the given key in the same meta prefix.
	return key.Next(), proto.Key(key[:len(Meta1Prefix)]).PrefixEnd(), nil
}

// addKeyRange adds the specified key range to the interval cache,
// taking care not to add this range if existing entries already
// completely cover the range.
func (tm *txnMetadata) addKeyRange(start, end proto.Key) {
	// This gives us a memory-efficient end key if end is empty.
	// The most common case for keys in the intents interval map
	// is for single keys. However, the interval cache requires
	// a non-empty interval, so we create two key slices which
	// share the same underlying byte array.
	if len(end) == 0 {
		end = start.Next()
		start = end[:len(start)]
	}
	key := tm.keys.NewKey(start, end)
	for _, o := range tm.keys.GetOverlaps(start, end) {
		if o.Key.Contains(key) {
			return
		} else if key.Contains(o.Key) {
			tm.keys.Del(o.Key)
		}
	}

	// Since no existing key range fully covered this range, add it now.
	tm.keys.Add(key, nil)
}

// getCachedRangeDescriptorLocked is a helper function to retrieve the
// descriptor of the range which contains the given key, if present in the
// cache. It is assumed that the caller holds a read lock on rdc.rangeCacheMu.
func (rdc *rangeDescriptorCache) getCachedRangeDescriptorLocked(key proto.Key, isReverse bool) (
	rangeCacheKey, *proto.RangeDescriptor) {
	// The cache is indexed using the end-key of the range, but the
	// end-key is non-inclusive.
	var metaKey proto.Key
	if !isReverse {
		// If it is not reverse scan, we access the cache using key.Next().
		metaKey = keys.RangeMetaKey(key.Next())
	} else {
		// Because reverse scan request is begining at end key(exclusive),so we
		// access the cache using key directly.
		metaKey = keys.RangeMetaKey(key)
	}

	k, v, ok := rdc.rangeCache.Ceil(rangeCacheKey(metaKey))
	if !ok {
		return nil, nil
	}
	metaEndKey := k.(rangeCacheKey)
	rd := v.(*proto.RangeDescriptor)

	// Check that key actually belongs to the range.
	if !rd.ContainsKey(keys.KeyAddress(key)) {
		// The key is the EndKey of the range in reverse scan, just return the range descriptor.
		if isReverse && key.Equal(rd.EndKey) {
			return metaEndKey, rd
		}
		return nil, nil
	}

	// The key is the StartKey of the range in reverse scan. We need to return the previous range
	// descriptor, but it is not in the cache yet.
	if isReverse && key.Equal(rd.StartKey) {
		return nil, nil
	}
	return metaEndKey, rd
}