/// <summary>
/// Do checkpoint operation to copy log pages into data file. Return how many transactions was commited inside data file
/// If soft = true, just try enter in exclusive mode - if not possible, just exit
/// </summary>
public void Checkpoint(bool soft)
{
// get original log length
var logLength = _disk.GetLength(FileOrigin.Log);
// no log file or no confirmed transaction, just exit
if (logLength == 0 || _confirmTransactions.Count == 0)
{
return;
}
// for safe, lock all database (read/write) before run checkpoint operation
// future versions can be smarter and avoid lock (be more like SQLite checkpoint)
if (soft)
{
// shutdown mode only try enter in exclusive mode... if not possible, exit without checkpoint
if (_locker.TryEnterExclusive() == false)
{
return;
}
}
else
{
_locker.EnterReserved(true);
}
LOG($"checkpoint", "WAL");
// wait all pages write on disk
_disk.Queue.Wait();
ENSURE(_disk.Queue.Length == 0, "no pages on queue when checkpoint");
// getting all "good" pages from log file to be copied into data file
IEnumerable <PageBuffer> source()
{
foreach (var buffer in _disk.ReadFull(FileOrigin.Log))
{
// read direct from buffer to avoid create BasePage structure
var transactionID = buffer.ReadUInt32(BasePage.P_TRANSACTION_ID);
// only confied paged can be write on data disk
if (_confirmTransactions.Contains(transactionID))
{
var pageID = buffer.ReadUInt32(BasePage.P_PAGE_ID);
// clear isConfirmed/transactionID
buffer.Write(uint.MaxValue, BasePage.P_TRANSACTION_ID);
buffer.Write(false, BasePage.P_IS_CONFIRMED);
buffer.Position = BasePage.GetPagePosition(pageID);
yield return(buffer);
}
}
}
// write all log pages into data file (sync)
_disk.Write(source(), FileOrigin.Data);
// reset
_confirmTransactions.Clear();
_index.Clear();
_currentReadVersion = 0;
// clear cache
_disk.Cache.Clear();
// clear log file (sync)
_disk.SetLength(0, FileOrigin.Log);
// remove exclusive lock
_locker.ExitReserved(true);
}
/// <summary>
/// Do checkpoint operation to copy log pages into data file. Return how many pages as saved into data file
/// Soft checkpoint try execute only if there is no one using (try exclusive lock - if not possible just exit)
/// If crop = true, reduce data file removing all log area. If not, keeps file with same size and clean all isConfirmed pages
/// </summary>
public int Checkpoint(bool soft, bool crop)
{
LOG($"checkpoint", "WAL");
bool lockWasTaken;
if (soft)
{
if (_locker.TryEnterExclusive(out lockWasTaken) == false)
{
return(0);
}
}
else
{
lockWasTaken = _locker.EnterExclusive();
}
try
{
// wait all pages write on disk
_disk.Queue.Wait();
var counter = 0;
ENSURE(_disk.Queue.Length == 0, "no pages on queue when checkpoint");
// getting all "good" pages from log file to be copied into data file
IEnumerable <PageBuffer> source()
{
// collect all isConfirmedPages
var confirmedPages = new List <long>();
var finalDataPosition = (_disk.Header.LastPageID + 1) * PAGE_SIZE;
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);
}
}
// if not crop data file, fill with 0 all confirmed pages after data area
if (crop == false)
{
var buffer = new PageBuffer(new byte[PAGE_SIZE], 0, 0);
foreach (var position in confirmedPages)
{
buffer.Position = position;
yield return(buffer);
}
}
}
// write all log pages into data file (sync)
_disk.Write(source());
// clear log file, clear wal index, memory cache,
this.Clear(crop);
return(counter);
}
finally
{
if (lockWasTaken)
{
_locker.ExitExclusive();
}
}
}