/// <summary>
/// The second layer of the search tree is a table file's block index of keys. The block index is part of the table
/// file's metadata which is located at the end of its physical data file. The index contains one entry for each
/// logical data block within the table file. The entry contains the last key in the block and the offset of the block
/// within the table file. leveldb performs a binary search of the block index to locate a candidate data block. It
/// reads the candidate data block from the table file.
/// </summary>
public static Footer Read(Stream stream)
{
stream.Seek(-FooterLength, SeekOrigin.End);
Span <byte> footer = new byte[FooterLength];
stream.Read(footer);
var reader = new SpanReader(footer);
var metaIndexHandle = BlockHandle.ReadBlockHandle(ref reader);
var indexHandle = BlockHandle.ReadBlockHandle(ref reader);
reader.Seek(-sizeof(ulong), SeekOrigin.End);
ReadOnlySpan <byte> magic = reader.Read(8);
if (Magic.AsSpan().SequenceCompareTo(magic) != 0)
{
throw new Exception("Invalid footer. Magic end missing. This is not a proper table file");
}
return(new Footer(metaIndexHandle, indexHandle));
}
/// <summary>
/// The second layer of the search tree is a table file's block index of keys. The block index is part of the table
/// file's metadata which is located at the end of its physical data file. The index contains one entry for each
/// logical data block within the table file. The entry contains the last key in the block and the offset of the block
/// within the table file. leveldb performs a binary search of the block index to locate a candidate data block. It
/// reads the candidate data block from the table file.
/// </summary>
public static Footer Read(MemoryMappedViewStream stream)
{
stream.Seek(-FooterLength, SeekOrigin.End);
Span <byte> footer = new byte[FooterLength];
stream.Read(footer);
SpanReader reader = new SpanReader(footer);
BlockHandle metaIndexHandle = BlockHandle.ReadBlockHandle(ref reader);
BlockHandle indexHandle = BlockHandle.ReadBlockHandle(ref reader);
reader.Seek(-sizeof(ulong), SeekOrigin.End);
var magic = reader.ReadUInt64();
if (Magic != magic)
{
throw new Exception("Invalid footer. Magic end missing. This is not a proper table file");
}
return(new Footer(metaIndexHandle, indexHandle));
}