private long? TryFindLargeValue(Transaction tx, TreeIterator it, int num)
{
int numberOfNeededFullSections = num / NumberOfPagesInSection;
int numberOfExtraBitsNeeded = num % NumberOfPagesInSection;
int foundSections = 0;
MemorySlice startSection = null;
long? startSectionId = null;
var sections = new List<Slice>();
do
{
var stream = it.CreateReaderForCurrent();
{
var current = new StreamBitArray(stream);
var currentSectionId = it.CurrentKey.CreateReader().ReadBigEndianInt64();
//need to find full free pages
if (current.SetCount < NumberOfPagesInSection)
{
ResetSections(ref foundSections, sections, ref startSection, ref startSectionId);
continue;
}
//those sections are not following each other in the memory
if (startSectionId != null && currentSectionId != startSectionId + foundSections)
{
ResetSections(ref foundSections, sections, ref startSection, ref startSectionId);
}
//set the first section of the sequence
if (startSection == null)
{
startSection = it.CurrentKey;
startSectionId = currentSectionId;
}
sections.Add(it.CurrentKey);
foundSections++;
if (foundSections != numberOfNeededFullSections)
continue;
//we found enough full sections now we need just a bit more
if (numberOfExtraBitsNeeded == 0)
{
foreach (var section in sections)
{
tx.FreeSpaceRoot.Delete(section);
}
return startSectionId * NumberOfPagesInSection;
}
var nextSectionId = currentSectionId + 1;
var nextId = new Slice(EndianBitConverter.Big.GetBytes(nextSectionId));
var read = tx.FreeSpaceRoot.Read(nextId);
if (read == null)
{
//not a following next section
ResetSections(ref foundSections, sections, ref startSection, ref startSectionId);
continue;
}
var next = new StreamBitArray(read.Reader);
if (next.HasStartRangeCount(numberOfExtraBitsNeeded) == false)
{
//not enough start range count
ResetSections(ref foundSections, sections, ref startSection, ref startSectionId);
continue;
}
//mark selected bits to false
if (next.SetCount == numberOfExtraBitsNeeded)
{
tx.FreeSpaceRoot.Delete(nextId);
}
else
{
for (int i = 0; i < numberOfExtraBitsNeeded; i++)
{
next.Set(i, false);
}
tx.FreeSpaceRoot.Add(nextId, next.ToStream());
}
foreach (var section in sections)
{
tx.FreeSpaceRoot.Delete(section);
}
return startSectionId * NumberOfPagesInSection;
}
} while (it.MoveNext());
return null;
}
private long? TryFindSmallValue(Transaction tx, TreeIterator it, int num)
{
do
{
var stream = it.CreateReaderForCurrent();
{
var current = new StreamBitArray(stream);
var currentSectionId = it.CurrentKey.CreateReader().ReadBigEndianInt64();
long? page;
if (current.SetCount < num)
{
if (TryFindSmallValueMergingTwoSections(tx, it.CurrentKey, num, current, currentSectionId, out page))
return page;
continue;
}
if (TryFindContinuousRange(tx, it, num, current, currentSectionId, out page))
return page;
//could not find a continuous so trying to merge
if (TryFindSmallValueMergingTwoSections(tx, it.CurrentKey, num, current, currentSectionId, out page))
return page;
}
} while (it.MoveNext());
return null;
}
private bool TryFindContinuousRange(Transaction tx, TreeIterator it, int num, StreamBitArray current, long currentSectionId, out long? page)
{
page = -1;
var start = -1;
var count = 0;
for (int i = 0; i < NumberOfPagesInSection; i++)
{
if (current.Get(i))
{
if (start == -1)
start = i;
count++;
if (count == num)
{
page = currentSectionId * NumberOfPagesInSection + start;
break;
}
}
else
{
start = -1;
count = 0;
}
}
if (count != num)
return false;
if (current.SetCount == num)
{
tx.FreeSpaceRoot.Delete(it.CurrentKey);
}
else
{
for (int i = 0; i < num; i++)
{
current.Set(i + start, false);
}
tx.FreeSpaceRoot.Add(it.CurrentKey, current.ToStream());
}
return true;
}
private static bool TryFindSmallValueMergingTwoSections(Transaction tx, TreeIterator it, int num, StreamBitArray current, long currentSectionId, out long? result)
{
result = -1;
var currentRange = current.GetEndRangeCount();
if (currentRange == 0)
return false;
var nextSectionId = currentSectionId + 1;
var nextId = new Slice(EndianBitConverter.Big.GetBytes(nextSectionId));
var read = tx.State.FreeSpaceRoot.Read(nextId);
if (read == null)
return false;
var next = new StreamBitArray(read.Reader);
var nextRange = num - currentRange;
if (next.HasStartRangeCount(nextRange) == false)
return false;
if (next.SetCount == nextRange)
{
tx.State.FreeSpaceRoot.Delete(nextId);
}
else
{
for (int i = 0; i < nextRange; i++)
{
next.Set(i, false);
}
tx.State.FreeSpaceRoot.Add(nextId, next.ToStream());
}
if (current.SetCount == currentRange)
{
tx.State.FreeSpaceRoot.Delete(it.CurrentKey);
}
else
{
for (int i = 0; i < currentRange; i++)
{
current.Set(NumberOfPagesInSection - 1 - i, false);
}
tx.State.FreeSpaceRoot.Add(nextId, next.ToStream());
}
result = currentSectionId * NumberOfPagesInSection + currentRange;
return true;
}