/// <summary>
/// Get a new empty page from disk: can be a reused page (from header free list) or file extend
/// Never re-use page from same transaction
/// </summary>
public T NewPage <T>()
where T : BasePage
{
ENSURE(_collectionPage == null, typeof(T) == typeof(CollectionPage), "if no collection page defined yet, must be first request");
ENSURE(typeof(T) == typeof(CollectionPage), _collectionPage == null, "there is no new collection page if page already exists");
var pageID = 0u;
PageBuffer buffer;
// lock header instance to get new page
lock (_header)
{
// there is need for _header.Savepoint() because changes here will incremental and will be persist later
// if any problem occurs here, rollback will catch this changes
// try get page from Empty free list
if (_header.FreeEmptyPageList != uint.MaxValue)
{
var free = this.GetPage <BasePage>(_header.FreeEmptyPageList);
ENSURE(free.PageType == PageType.Empty, "empty page must be defined as empty type");
// set header free empty page to next free page
_header.FreeEmptyPageList = free.NextPageID;
// clear NextPageID
free.NextPageID = uint.MaxValue;
// get pageID from empty list
pageID = free.PageID;
// get buffer inside re-used page
buffer = free.Buffer;
}
else
{
// checks if not exceeded data file limit size
var newLength = (_header.LastPageID + 1) * PAGE_SIZE;
if (newLength > _header.Pragmas.LimitSize)
{
throw new LiteException(0, $"Maximum data file size has been reached: {FileHelper.FormatFileSize(_header.Pragmas.LimitSize)}");
}
// increase LastPageID from shared page
pageID = ++_header.LastPageID;
// request for a new buffer
buffer = _reader.NewPage();
}
// retain a list of created pages to, in a rollback situation, back pages to empty list
_transPages.NewPages.Add(pageID);
}
var page = BasePage.CreatePage <T>(buffer, pageID);
// update local cache with new instance T page type
if (page.PageType != PageType.Collection)
{
_localPages[pageID] = page;
}
// define ColID for this new page (if this.CollectionPage is null, so this is new collection page)
page.ColID = _collectionPage?.PageID ?? page.PageID;
// define as dirty to override pageType
page.IsDirty = true;
// increment transaction size
_transPages.TransactionSize++;
return(page);
}
/// <summary>
/// Return added pages when occurs an rollback transaction (run this only in rollback). Create new transactionID and add into
/// Log file all new pages as EmptyPage in a linked order - also, update SharedPage before store
/// </summary>
private void ReturnNewPages()
{
// create new transaction ID
var transactionID = _walIndex.NextTransactionID();
// now lock header to update LastTransactionID/FreePageList
lock (_header)
{
// persist all empty pages into wal-file
var pagePositions = new Dictionary <uint, PagePosition>();
IEnumerable <PageBuffer> source()
{
// create list of empty pages with forward link pointer
for (var i = 0; i < _transPages.NewPages.Count; i++)
{
var pageID = _transPages.NewPages[i];
var next = i < _transPages.NewPages.Count - 1 ? _transPages.NewPages[i + 1] : _header.FreeEmptyPageList;
var buffer = _disk.Cache.NewPage();
var page = new BasePage(buffer, pageID, PageType.Empty)
{
NextPageID = next,
TransactionID = transactionID
};
yield return(page.UpdateBuffer());
// update wal
pagePositions[pageID] = new PagePosition(pageID, buffer.Position);
}
// update header page with my new transaction ID
_header.TransactionID = transactionID;
_header.FreeEmptyPageList = _transPages.NewPages[0];
_header.IsConfirmed = true;
// clone header buffer
var buf = _header.UpdateBuffer();
var clone = _disk.Cache.NewPage();
Buffer.BlockCopy(buf.Array, buf.Offset, clone.Array, clone.Offset, clone.Count);
yield return(clone);
};
// create a header save point before any change
var safepoint = _header.Savepoint();
try
{
// write all pages (including new header)
_disk.WriteAsync(source());
}
catch
{
// must revert all header content if any error occurs during header change
_header.Restore(safepoint);
throw;
}
// now confirm this transaction to wal
_walIndex.ConfirmTransaction(transactionID, pagePositions.Values);
}
}
/// <summary>
/// Update document using same page position as reference
/// </summary>
public void Update(CollectionPage col, PageAddress blockAddress, BsonDocument doc)
{
var bytesLeft = doc.GetBytesCount(true);
if (bytesLeft > MAX_DOCUMENT_SIZE) throw new LiteException(0, "Document size exceed {0} limit", MAX_DOCUMENT_SIZE);
DataBlock lastBlock = null;
var updateAddress = blockAddress;
IEnumerable <BufferSlice> source()
{
var bytesToCopy = 0;
while (bytesLeft > 0)
{
// if last block contains new block sequence, continue updating
if (updateAddress.IsEmpty == false)
{
var dataPage = _snapshot.GetPage<DataPage>(updateAddress.PageID);
var currentBlock = dataPage.GetBlock(updateAddress.Index);
// try get full page size content (do not add DATA_BLOCK_FIXED_SIZE because will be added in UpdateBlock)
bytesToCopy = Math.Min(bytesLeft, dataPage.FreeBytes + currentBlock.Buffer.Count);
// get current free slot linked list
var slot = BasePage.FreeIndexSlot(dataPage.FreeBytes);
var updateBlock = dataPage.UpdateBlock(currentBlock, bytesToCopy);
_snapshot.AddOrRemoveFreeList(dataPage, slot);
yield return updateBlock.Buffer;
lastBlock = updateBlock;
// go to next address (if exists)
updateAddress = updateBlock.NextBlock;
}
else
{
bytesToCopy = Math.Min(bytesLeft, MAX_DATA_BYTES_PER_PAGE);
var dataPage = _snapshot.GetFreePage<DataPage>(bytesToCopy + DataBlock.DATA_BLOCK_FIXED_SIZE);
var insertBlock = dataPage.InsertBlock(bytesToCopy, true);
if (lastBlock != null)
{
lastBlock.SetNextBlock(insertBlock.Position);
}
yield return insertBlock.Buffer;
lastBlock = insertBlock;
}
bytesLeft -= bytesToCopy;
}
// old document was bigger than current, must delete extend blocks
if (lastBlock.NextBlock.IsEmpty == false)
{
var nextBlockAddress = lastBlock.NextBlock;
lastBlock.SetNextBlock(PageAddress.Empty);
this.Delete(nextBlockAddress);
}
}
// consume all source bytes to write BsonDocument direct into PageBuffer
// must be fastest as possible
using (var w = new BufferWriter(source()))
{
// already bytes count calculate at method start
w.WriteDocument(doc, false);
w.Consume();
}
}
