/// <summary>
/// Persist all dirty in-memory pages (in all snapshots) and clear local pages list (even clean pages)
/// </summary>
private async Task <int> PersistDirtyPages(bool commit)
{
var dirty = 0;
// inner method to get all dirty pages
IEnumerable <PageBuffer> source()
{
// get all dirty pages from all write snapshots
// can include (or not) collection pages
// update DirtyPagesLog inside transPage for all dirty pages was write on disk
var pages = _snapshots.Values
.Where(x => x.Mode == LockMode.Write)
.SelectMany(x => x.GetWritablePages(true, commit));
// mark last dirty page as confirmed only if there is no header change in commit
var markLastAsConfirmed = commit && _transPages.HeaderChanged == false;
// neet use "IsLast" method to get when loop are last item
foreach (var page in pages.IsLast())
{
// update page transactionID
page.Item.TransactionID = _transactionID;
// if last page, mask as confirm (only if a real commit and no header changes)
if (page.IsLast)
{
page.Item.IsConfirmed = markLastAsConfirmed;
}
// if current page is last deleted page, point this page to last free
if (_transPages.LastDeletedPageID == page.Item.PageID && commit)
{
ENSURE(_transPages.HeaderChanged, "must header be in lock");
ENSURE(page.Item.PageType == PageType.Empty, "must be marked as deleted page");
// join existing free list pages into new list of deleted pages
page.Item.NextPageID = _header.FreeEmptyPageList;
// and now, set header free list page to this new list
_header.FreeEmptyPageList = _transPages.FirstDeletedPageID;
}
var buffer = page.Item.UpdateBuffer();
// buffer position will be set at end of file (it´s always log file)
yield return(buffer);
dirty++;
_transPages.DirtyPages[page.Item.PageID] = new PagePosition(page.Item.PageID, buffer.Position);
}
// in commit with header page change, last page will be header
if (commit && _transPages.HeaderChanged)
{
// update this confirm page with current transactionID
_header.TransactionID = _transactionID;
// this header page will be marked as confirmed page in log file
_header.IsConfirmed = true;
// invoke all header callbacks (new/drop collections)
_transPages.OnCommit(_header);
// clone header page
var buffer = _header.UpdateBuffer();
var clone = _disk.Cache.NewPage();
// mem copy from current header to new header clone
Buffer.BlockCopy(buffer.Array, buffer.Offset, clone.Array, clone.Offset, clone.Count);
// persist header in log file
yield return(clone);
}
};
// write all dirty pages, in sequence on log-file and store references into log pages on transPages
// (works only for Write snapshots)
var count = await _disk.WriteLogPages(source());
// now, discard all clean pages (because those pages are writable and must be readable)
// from write snapshots
_disk.Cache.DiscardCleanPages(_snapshots.Values
.Where(x => x.Mode == LockMode.Write)
.SelectMany(x => x.GetWritablePages(false, commit))
.Select(x => x.Buffer));
return(count);
}