private Page DiskReadPage(string tableName, int pageIndex, int fileId)
{
string filename = DatabaseName + "." + tableName + ".data." + fileId;
DataFileHeader tableDataFileHeader = ReadDataFileHeader(tableName, fileId);
if (pageIndex >= tableDataFileHeader.TotalPageNum)
throw new ApplicationException("pageIndex");
var p = new Page(tableDataFileHeader)
{
FileId = fileId,
PageIndex = pageIndex,
PageSize = tableDataFileHeader.PageSize,
TableName = tableName,
DataFileName = filename,
};
using (var fileStream = new FileStream(filename, FileMode.Open))
{
fileStream.Seek(DataFileHeaderSize + pageIndex * p.PageSize, SeekOrigin.Begin);
var pageData = new byte[p.PageSize];
fileStream.Read(pageData, 0, p.PageSize);
p.Decode(pageData);
}
return p;
}
private void DiskWritePage(string tableName, Page page, int fileId)
{
string filename = DatabaseName + "." + page.TableName + ".data." + fileId;
DataFileHeader tableDataFileHeader = ReadDataFileHeader(tableName, page.FileId);
if (page.PageIndex >= tableDataFileHeader.TotalPageNum)
throw new ApplicationException("pageIndex");
page.FileId = fileId;
using (var fileStream = new FileStream(filename, FileMode.Open))
{
fileStream.Seek(DataFileHeaderSize + page.PageIndex * page.PageSize, SeekOrigin.Begin);
byte[] pageData = page.Encode();
fileStream.Write(pageData, 0, page.PageSize);
fileStream.Flush();
}
}
/// <summary>
/// Write page into the shadow and create an updated page tableName for it
/// </summary>
public void WritePage(Transaction tid, string tableName, string key, Page page)
{
EnsureInitialized();
if (page.TableName != tableName)
throw new ArgumentException("page deson't below to the tableName");
//read active page tableName
var pageTable = this.DiskReadPageTable(tableName);
//modify page tableName
var pageTableIndex = (from k in pageTable.RecordIndices where Trim(k.Key) == key select k).Single();
pageTableIndex.ShadowFileId = pageTableIndex.ActiveFileId == 0 ? 1 : 0;
if (pageTableIndex.PageIndex != page.PageIndex)
throw new ApplicationException("index doesn't match the page");
//save page into shadow
DiskWritePage(tableName, page, pageTableIndex.ShadowFileId);
//save page tableName file
DiskWritePageTable(tableName, pageTable);
}