private bool TryUseExistingPrefix(MemorySlice key, out PrefixedSlice prefixedSlice)
{
if (_prefixSection->NextPrefixId < 1)
{
prefixedSlice = null;
return(false);
}
var prefix = new PrefixNode();
BestPrefixMatch bestMatch = null;
for (byte prefixId = 0; prefixId < _prefixSection->NextPrefixId; prefixId++)
{
AssertPrefixNode(prefixId);
prefix.Set(_base + _prefixSection->PrefixOffsets[prefixId], PageNumber);
var length = key.FindPrefixSize(new Slice(prefix.ValuePtr, prefix.PrefixLength));
if (length == 0)
{
continue;
}
if (length == prefix.PrefixLength) // full prefix usage
{
prefixedSlice = new PrefixedSlice(prefixId, length, key.Skip(length));
return(true);
}
// keep on looking for a better prefix
if (bestMatch == null)
{
bestMatch = new BestPrefixMatch
{
PrefixId = prefixId,
PrefixUsage = length
};
}
else if (length > bestMatch.PrefixUsage)
{
bestMatch.PrefixId = prefixId;
bestMatch.PrefixUsage = length;
}
}
if (bestMatch != null && bestMatch.PrefixUsage > MinPrefixLength(key))
{
prefixedSlice = new PrefixedSlice(bestMatch.PrefixId, bestMatch.PrefixUsage, key.Skip(bestMatch.PrefixUsage));
return(true);
}
prefixedSlice = null;
return(false);
}
private bool TryCreateNewPrefix(MemorySlice key, int nodeIndex, out PrefixedSlice prefixedSlice)
{
if (_prefixSection->NextPrefixId >= PrefixCount || NumberOfEntries == 0)
{
prefixedSlice = null;
return false;
}
MemorySlice left;
MemorySlice right;
if (nodeIndex > 0 && nodeIndex < NumberOfEntries) // middle
{
left = GetNodeKey(nodeIndex - 1);
right = GetNodeKey(nodeIndex);
}
else if (nodeIndex == 0) // first
{
left = null;
right = GetNodeKey(0);
}
else if (nodeIndex == NumberOfEntries) // last
{
left = GetNodeKey(nodeIndex - 1);
right = null;
}
else
throw new NotSupportedException("Invalid node index prefix: " + nodeIndex + ". Number of entries: " + NumberOfEntries);
ushort leftLength = 0;
ushort rightLength = 0;
if (left != null && left.Size > 0) // not before all keys
leftLength = key.FindPrefixSize(left);
if (right != null)
rightLength = key.FindPrefixSize(right);
var minPrefixLength = MinPrefixLength(key);
if (left != null && leftLength > minPrefixLength && leftLength > rightLength)
{
prefixedSlice = new PrefixedSlice(_prefixSection->NextPrefixId, leftLength, key.Skip(leftLength))
{
NewPrefix = new Slice(left.ToSlice(), leftLength)
};
return true;
}
if (right != null && rightLength > minPrefixLength && rightLength > leftLength)
{
prefixedSlice = new PrefixedSlice(_prefixSection->NextPrefixId, rightLength, key.Skip(rightLength))
{
NewPrefix = new Slice(right.ToSlice(), rightLength)
};
return true;
}
prefixedSlice = null;
return false;
}
private bool TryUseExistingPrefix(MemorySlice key, out PrefixedSlice prefixedSlice)
{
if (_prefixSection->NextPrefixId < 1)
{
prefixedSlice = null;
return false;
}
BestPrefixMatch bestMatch = null;
for (byte prefixId = 0; prefixId < _prefixSection->NextPrefixId; prefixId++)
{
AssertPrefixNode(prefixId);
var prefix = new PrefixNode();
prefix.Set(_base + _prefixSection->PrefixOffsets[prefixId], PageNumber);
var length = key.FindPrefixSize(new Slice(prefix.ValuePtr, prefix.PrefixLength));
if (length == 0)
continue;
if (length == prefix.PrefixLength) // full prefix usage
{
prefixedSlice = new PrefixedSlice(prefixId, length, key.Skip(length))
{
Prefix = prefix
};
return true;
}
// keep on looking for a better prefix
if (bestMatch == null)
{
bestMatch = new BestPrefixMatch
{
PrefixId = prefixId,
PrefixUsage = length,
PrefixNode = prefix
};
}
else if (length > bestMatch.PrefixUsage)
{
bestMatch.PrefixId = prefixId;
bestMatch.PrefixUsage = length;
bestMatch.PrefixNode = prefix;
}
}
if (bestMatch != null && bestMatch.PrefixUsage > MinPrefixLength(key))
{
prefixedSlice = new PrefixedSlice(bestMatch.PrefixId, bestMatch.PrefixUsage, key.Skip(bestMatch.PrefixUsage))
{
Prefix = bestMatch.PrefixNode
};
return true;
}
prefixedSlice = null;
return false;
}
private bool TryCreateNewPrefix(MemorySlice key, int nodeIndex, out PrefixedSlice prefixedSlice)
{
if (_prefixSection->NextPrefixId >= PrefixCount || NumberOfEntries == 0)
{
prefixedSlice = null;
return(false);
}
MemorySlice left;
MemorySlice right;
if (nodeIndex > 0 && nodeIndex < NumberOfEntries) // middle
{
left = GetNodeKey(nodeIndex - 1);
right = GetNodeKey(nodeIndex);
}
else if (nodeIndex == 0) // first
{
left = null;
right = GetNodeKey(0);
}
else if (nodeIndex == NumberOfEntries) // last
{
left = GetNodeKey(nodeIndex - 1);
right = null;
}
else
{
throw new NotSupportedException("Invalid node index prefix: " + nodeIndex + ". Number of entries: " + NumberOfEntries);
}
ushort leftLength = 0;
ushort rightLength = 0;
if (left != null && left.Size > 0) // not before all keys
{
leftLength = key.FindPrefixSize(left);
}
if (right != null)
{
rightLength = key.FindPrefixSize(right);
}
var minPrefixLength = MinPrefixLength(key);
if (left != null && leftLength > minPrefixLength && leftLength > rightLength)
{
prefixedSlice = new PrefixedSlice(_prefixSection->NextPrefixId, leftLength, key.Skip(leftLength))
{
NewPrefix = new Slice(left.ToSlice(), leftLength)
};
return(true);
}
if (right != null && rightLength > minPrefixLength && rightLength > leftLength)
{
prefixedSlice = new PrefixedSlice(_prefixSection->NextPrefixId, rightLength, key.Skip(rightLength))
{
NewPrefix = new Slice(right.ToSlice(), rightLength)
};
return(true);
}
prefixedSlice = null;
return(false);
}