/// <summary>
/// Read page from disk (dirty, wal or data)
/// </summary>
private T ReadPage <T>(uint pageID, out FileOrigin origin, out long position, out int walVersion)
where T : BasePage
{
// if not inside local pages can be a dirty page saved in log file
if (_transPages.DirtyPages.TryGetValue(pageID, out var walPosition))
{
// read page from log file
var buffer = _reader.ReadPage(walPosition.Position, _mode == LockMode.Write, FileOrigin.Log);
var dirty = BasePage.ReadPage <T>(buffer);
origin = FileOrigin.Log;
position = walPosition.Position;
walVersion = _readVersion;
ENSURE(dirty.TransactionID == _transactionID, "this page must came from same transaction");
return(dirty);
}
// now, look inside wal-index
var pos = _walIndex.GetPageIndex(pageID, _readVersion, out walVersion);
if (pos != long.MaxValue)
{
// read page from log file
var buffer = _reader.ReadPage(pos, _mode == LockMode.Write, FileOrigin.Log);
var logPage = BasePage.ReadPage <T>(buffer);
// clear some data inside this page (will be override when write on log file)
logPage.TransactionID = 0;
logPage.IsConfirmed = false;
origin = FileOrigin.Log;
position = pos;
return(logPage);
}
else
{
// for last chance, look inside original disk data file
var pagePosition = BasePage.GetPagePosition(pageID);
// read page from data file
var buffer = _reader.ReadPage(pagePosition, _mode == LockMode.Write, FileOrigin.Data);
var diskpage = BasePage.ReadPage <T>(buffer);
origin = FileOrigin.Data;
position = pagePosition;
ENSURE(diskpage.IsConfirmed == false || diskpage.TransactionID != 0, "page are not header-clear in data file");
return(diskpage);
}
}
/// <summary>
/// Read page from stream - do not use cache system
/// </summary>
private T ReadPage <T>(uint pageID)
where T : BasePage
{
var position = BasePage.GetPagePosition(pageID);
_stream.Position = position;
_stream.Read(_buffer, 0, PAGE_SIZE);
var buffer = new PageBuffer(_buffer, 0, 0);
return(BasePage.ReadPage <T>(buffer));
}
/// <summary>
/// Read page from stream - do not use cache system
/// </summary>
private T ReadPage <T>(uint pageID)
where T : BasePage
{
var position = BasePage.GetPagePosition(pageID);
if (_cachedPage?.PageID == pageID)
{
return((T)_cachedPage);
}
_stream.Position = position;
_stream.Read(_buffer, 0, PAGE_SIZE);
var buffer = new PageBuffer(_buffer, 0, 0);
return((T)(_cachedPage = BasePage.ReadPage <T>(buffer)));
}