func (s *sequenceHasher) loadClocks(hashValue uint64) (*storedClocks, error) {
stored := storedClocks{}
key := kHashPrefix + strconv.FormatUint(hashValue, 10)
bytes, cas, err := s.bucket.GetAndTouchRaw(key, base.SecondsToCbsExpiry(int(s.hashExpiry)))
IndexExpvars.Add("get_hashLoadClocks", 1)
if err != nil {
// Assume no clocks stored for this string
return &stored, nil
}
if err = stored.Unmarshal(bytes); err != nil {
base.Warn("Error unmarshalling stored clocks for key [%s], returning zero sequence", key)
return &stored, errors.New("Error unmarshalling stored clocks for key")
}
stored.cas = cas
return &stored, nil
}
func (s *sequenceHasher) GetHash(clock base.SequenceClock) (string, error) {
if clock == nil {
return "", errors.New("Can't calculate hash for nil clock")
}
hashValue := s.calculateHash(clock)
// Load stored clocks for this hash, to see if it's already been defined.
// Note: getCacheValue and load are handled as separate operations to optimize locking.
// 1. getCacheValue locks the cache, and retrieves the current cache entry (or creates a new empty entry if not found)
// 2. cachedValue.load locks the entry, and loads from the DB if no previous entry is found
cachedValue := s.getCacheValue(hashValue)
cachedClocks, err := cachedValue.load(s.loadClocks)
if err != nil {
return "", err
}
// Check whether the cached clocks for the hash value match our clock
exists, index := cachedClocks.Contains(clock.Value())
if exists {
seqHash := sequenceHash{
hashValue: hashValue,
collisionIndex: uint16(index),
}
IndexExpvars.Add("seqHash_getHash_hits", 1)
return seqHash.String(), nil
}
// Didn't find a match in cache - update the index and the cache. Get a write lock on the index value
// first, to ensure only one goroutine on this SG attempts to write. writeCas handling below handles
// the case where other SGs are updating the value concurrently
IndexExpvars.Add("seqHash_getHash_misses", 1)
// First copy the clock value, to ensure we store a non-mutable version in the cache
clockValue := make([]uint64, len(clock.Value()))
copy(clockValue, clock.Value())
updateErr := func() error {
cachedValue.lock.Lock()
defer cachedValue.lock.Unlock()
// If the number of cached clocks has changed, check whether someone else has added this clock
// while we waited for the lock
if len(cachedValue.clocks.Sequences) > len(cachedClocks.Sequences) {
exists, index = cachedValue.clocks.Contains(clockValue)
if exists {
return nil
}
}
// Add our clock to the cached clocks for this hash
existingClocks := cachedValue.clocks
existingClocks.Sequences = append(existingClocks.Sequences, clockValue)
// Update the hash entry in the bucket
key := kHashPrefix + strconv.FormatUint(hashValue, 10)
initialValue, err := existingClocks.Marshal()
index = len(existingClocks.Sequences) - 1
if err != nil {
return err
}
_, err = base.WriteCasRaw(s.bucket, key, initialValue, existingClocks.cas, base.SecondsToCbsExpiry(int(s.hashExpiry)), func(value []byte) (updatedValue []byte, err error) {
// Note: The following is invoked upon cas failure - may be called multiple times
base.LogTo("DIndex+", "CAS fail - reapplying changes for hash storage for key: %s", key)
var sClocks storedClocks
err = sClocks.Unmarshal(value)
if err != nil {
base.Warn("Error unmarshalling hash storage during update", err)
return nil, err
}
exists, index = sClocks.Contains(clockValue)
if exists {
// return empty byte array to cancel the update
return []byte{}, nil
}
// Not found - add
sClocks.Sequences = append(sClocks.Sequences, clockValue)
base.LogTo("DIndex+", "Reattempting stored hash write for key %s:", key)
index = len(sClocks.Sequences) - 1
return sClocks.Marshal()
})
return nil
}()
if updateErr != nil {
return "", updateErr
}
IndexExpvars.Add("writeCasRaw_hash", 1)
if err != nil && err.Error() != "Already Exists" {
return "", err
}
seqHash := &sequenceHash{
hashValue: hashValue,
collisionIndex: uint16(index),
}
return seqHash.String(), nil
}