public Snapshot(LockMode mode, string collectionName, HeaderPage header, uint transactionID, TransactionPages transPages, LockService locker, WalIndexService walIndex, DiskReader reader, bool addIfNotExists)
{
_mode = mode;
_collectionName = collectionName;
_header = header;
_transactionID = transactionID;
_transPages = transPages;
_locker = locker;
_walIndex = walIndex;
_reader = reader;
// enter in lock mode according initial mode
if (mode == LockMode.Read)
{
_locker.EnterRead(_collectionName);
}
else
{
_locker.EnterReserved(_collectionName);
}
// get lastest read version from wal-index
_readVersion = _walIndex.CurrentReadVersion;
var srv = new CollectionService(_header, this, _transPages);
// read collection (create if new - load virtual too)
srv.Get(_collectionName, addIfNotExists, ref _collectionPage);
// clear local pages (will clear _collectionPage link reference)
if (_collectionPage != null)
{
_localPages.Remove(_collectionPage.PageID);
}
}
/// <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);
}