private LogRecordPage ReadPage(ulong pageOffset)
{
if (m_firstTailPage == null || m_secondTailPage == null)
{
m_firstTailPage = ReadPageFromFile(m_restartPage.SystemPageSize * 2);
m_secondTailPage = ReadPageFromFile(m_restartPage.SystemPageSize * 2 + m_restartPage.LogPageSize);
}
LogRecordPage page = null;
if (pageOffset == m_firstTailPage.LastLsnOrFileOffset)
{
page = m_firstTailPage;
}
if (pageOffset == m_secondTailPage.LastLsnOrFileOffset)
{
if (page == null || m_secondTailPage.LastEndLsn >= m_firstTailPage.LastEndLsn)
{
page = m_secondTailPage;
}
}
if (page == null)
{
page = ReadPageFromFile(pageOffset);
}
return(page);
}
private void WritePage(ulong pageOffset, LogRecordPage page)
{
if (m_restartPage == null)
{
m_restartPage = ReadRestartPage();
}
byte[] pageBytes = page.GetBytes((int)m_restartPage.LogPageSize, m_restartPage.LogRestartArea.LogPageDataOffset);
WriteData(pageOffset, pageBytes);
}
public LogRecord ReadRecord(ulong lsn)
{
if (m_restartPage == null)
{
m_restartPage = ReadRestartPage();
}
ulong pageOffsetInFile = LsnToPageOffsetInFile(lsn);
int recordOffsetInPage = LsnToRecordOffsetInPage(lsn);
LogRecordPage page = ReadPage(pageOffsetInFile);
return(page.ReadRecord(recordOffsetInPage, m_restartPage.LogRestartArea.LogPageDataOffset));
}