/// <summary>
/// Do checkpoint operation to copy log pages into data file. Return how many pages as saved into data file
/// Soft checkpoint try execute only if there is no one using (try exclusive lock - if not possible just exit)
/// If crop = true, reduce data file removing all log area. If not, keeps file with same size and clean all isConfirmed pages
/// </summary>
public async Task <int> Checkpoint()
{
LOG($"checkpoint", "WAL");
var counter = 0;
// getting all "good" pages from log file to be copied into data file
async IAsyncEnumerable <PageBuffer> source()
{
// collect all isConfirmedPages
var confirmedPages = new List <long>();
var finalDataPosition = (_disk.Header.LastPageID + 1) * PAGE_SIZE;
await foreach (var buffer in _disk.ReadLog(false))
{
// read direct from buffer to avoid create BasePage structure
var transactionID = buffer.ReadUInt32(BasePage.P_TRANSACTION_ID);
// only confirmed pages can be write on data disk
if (_confirmTransactions.Contains(transactionID))
{
// if page is confirmed page and are after data area, add to list
var isConfirmed = buffer.ReadBool(BasePage.P_IS_CONFIRMED);
if (isConfirmed && buffer.Position >= finalDataPosition)
{
confirmedPages.Add(buffer.Position);
}
// clear isConfirmed/transactionID
buffer.Write(uint.MaxValue, BasePage.P_TRANSACTION_ID);
buffer.Write(false, BasePage.P_IS_CONFIRMED);
// update buffer position to data area position
var pageID = buffer.ReadUInt32(BasePage.P_PAGE_ID);
buffer.Position = BasePage.GetPagePosition(pageID);
counter++;
yield return(buffer);
}
}
}
// write all log pages into data file (sync)
await _disk.WriteDataPages(source());
// clear log file, clear wal index, memory cache,
_confirmTransactions.Clear();
_index.Clear();
_lastTransactionID = 0;
_currentReadVersion = 0;
// clear cache
_disk.Cache.Clear();
_disk.ResetLogPosition(true);
return(counter);
}
