public static void CopyToPage(CompressionResult compressed, TreePage dest)
{
// let us copy the compressed values at the end of the page
// so we will handle additional, uncompressed values as usual
var writePtr = dest.Base + dest.PageSize - Constants.Compression.HeaderSize;
var header = (CompressedNodesHeader *)writePtr;
*header = compressed.Header;
writePtr -= header->SectionSize;
Memory.Copy(writePtr, compressed.CompressionOutputPtr, compressed.Header.CompressedSize + header->NumberOfCompressedEntries * Constants.Tree.NodeOffsetSize);
dest.Flags |= PageFlags.Compressed;
dest.Lower = (ushort)Constants.Tree.PageHeaderSize;
dest.Upper = (ushort)(writePtr - dest.Base);
Debug.Assert((dest.Upper & 1) == 0);
}
public static void CopyToPage(CompressionResult compressed, TreePage dest)
{
// let us copy the compressed values at the end of the page
// so we will handle additional, uncompressed values as usual
if (compressed.CompressionOutputPtr != null)
{
Debug.Assert(compressed.Header.CompressedSize > 0, "compressed.Header.CompressedSize > 0, value: " + compressed.Header.CompressedSize);
var writePtr = dest.Base + dest.PageSize - Constants.Compression.HeaderSize;
var header = (CompressedNodesHeader *)writePtr;
* header = compressed.Header;
writePtr -= header->SectionSize;
Memory.Copy(writePtr, compressed.CompressionOutputPtr,
compressed.Header.CompressedSize + header->NumberOfCompressedEntries * Constants.Tree.NodeOffsetSize);
dest.Flags |= PageFlags.Compressed;
dest.Lower = (ushort)Constants.Tree.PageHeaderSize;
dest.Upper = (ushort)(writePtr - dest.Base);
Debug.Assert((dest.Upper & 1) == 0);
}
else
{
Debug.Assert(compressed.Header.CompressedSize == 0, "compressed.Header.CompressedSize == 0, value: " + compressed.Header.CompressedSize);
if (compressed.CompressedPage.NumberOfEntries != 0)
{
ThrowNullCompressionOutputButNonEmptyPage(compressed.CompressedPage);
}
dest.Lower = (ushort)Constants.Tree.PageHeaderSize;
dest.Upper = (ushort)dest.PageSize;
dest.Flags &= ~PageFlags.Compressed;
}
}
public static IDisposable TryGetCompressedTempPage(LowLevelTransaction tx, TreePage page, out CompressionResult result, bool defrag = true)
{
if (defrag)
{
if (page.CalcSizeUsed() != page.SizeUsed - Constants.Tree.PageHeaderSize) // check if the page really requires defrag
{
page.Defrag(tx);
}
}
var valuesSize = page.PageSize - page.Upper;
TemporaryPage temp;
var returnTempPage = tx.Environment.GetTemporaryPage(tx, out temp);
var tempPage = temp.GetTempPage();
var compressionInput = page.Base + page.Upper;
var compressionResult = tempPage.Base + Constants.Tree.PageHeaderSize + Constants.Compression.HeaderSize; // temp compression result has compressed values at the beginning of the page
var offsetsSize = page.NumberOfEntries * Constants.Tree.NodeOffsetSize;
var compressionOutput = compressionResult + offsetsSize;
var compressedSize = LZ4.Encode64(
compressionInput,
compressionOutput,
valuesSize,
tempPage.PageSize - (Constants.Tree.PageHeaderSize + Constants.Compression.HeaderSize) - offsetsSize);
if (compressedSize == 0 || compressedSize > valuesSize)
{
// output buffer size not enough or compressed output size is greater than uncompressed input
result = null;
return(returnTempPage);
}
var compressedOffsets = (ushort *)compressionResult;
var offsets = page.KeysOffsets;
for (var i = 0; i < page.NumberOfEntries; i++)
{
compressedOffsets[i] = (ushort)(offsets[i] - page.Upper);
}
var compressionSectionSize = compressedSize + offsetsSize;
var sizeLeftInDecompressedPage = Constants.Compression.MaxPageSize - page.SizeUsed;
var sizeLeftForUncompressedEntries = tx.PageSize - (Constants.Tree.PageHeaderSize + Constants.Compression.HeaderSize + compressionSectionSize);
if (sizeLeftForUncompressedEntries > sizeLeftInDecompressedPage)
{
// expand compression section to prevent from adding next uncompressed entries what would result in
// exceeding MaxPageSize after the decompression
compressionSectionSize += sizeLeftForUncompressedEntries - sizeLeftInDecompressedPage;
}
compressionSectionSize += compressionSectionSize & 1; // ensure 2-byte alignment
// check that after decompression we won't exceed MaxPageSize
Debug.Assert(page.SizeUsed + // page header, node offsets, existing entries
(tx.PageSize - // space that can be still used to insert next uncompressed entries
(Constants.Tree.PageHeaderSize + Constants.Compression.HeaderSize + compressionSectionSize))
<= Constants.Compression.MaxPageSize);
Memory.Copy(tempPage.Base, page.Base, Constants.Tree.PageHeaderSize);
tempPage.Lower = (ushort)(Constants.Tree.PageHeaderSize + Constants.Compression.HeaderSize + compressionSectionSize);
tempPage.Upper = (ushort)tempPage.PageSize;
Debug.Assert(tempPage.Lower <= tempPage.Upper);
result = new CompressionResult
{
CompressedPage = tempPage,
CompressionOutputPtr = compressionResult,
Header = new CompressedNodesHeader
{
SectionSize = (ushort)compressionSectionSize,
CompressedSize = (ushort)compressedSize,
UncompressedSize = (ushort)valuesSize,
NumberOfCompressedEntries = page.NumberOfEntries,
}
};
return(returnTempPage);
}
