public TreePage Execute(TreePage page)
{
using (DisableFreeSpaceUsageIfSplittingRootTree())
{
_tree.ClearPagesCache();
if (_cursor.PageCount <= 1) // the root page
{
RebalanceRoot(page);
return(null);
}
_cursor.Pop();
var parentPage = _tree.ModifyPage(_cursor.CurrentPage);
_cursor.Update(_cursor.Pages, parentPage);
if (page.NumberOfEntries == 0) // empty page, just delete it and fixup parent
{
// need to change the implicit left page
if (parentPage.LastSearchPosition == 0 && parentPage.NumberOfEntries > 2)
{
var newImplicit = parentPage.GetNode(1)->PageNumber;
parentPage.RemoveNode(0);
parentPage.ChangeImplicitRefPageNode(newImplicit);
}
else // will be set to rights by the next rebalance call
{
parentPage.RemoveNode(parentPage.LastSearchPositionOrLastEntry);
}
_tree.FreePage(page);
return(parentPage);
}
if (page.IsBranch && page.NumberOfEntries == 1)
{
RemoveBranchWithOneEntry(page, parentPage);
return(parentPage);
}
var minKeys = page.IsBranch ? 2 : 1;
if ((page.UseMoreSizeThan(_tx.DataPager.PageMinSpace)) && page.NumberOfEntries >= minKeys)
{
return(null); // above space/keys thresholds
}
Debug.Assert(parentPage.NumberOfEntries >= 2); // if we have less than 2 entries in the parent, the tree is invalid
var sibling = SetupMoveOrMerge(page, parentPage);
Debug.Assert(sibling.PageNumber != page.PageNumber);
if (page.TreeFlags != sibling.TreeFlags)
{
return(null);
}
if (sibling.IsCompressed)
{
return(null);
}
if (sibling.PageSize != page.PageSize)
{
// if the current page is compressed (but already opened), we need to
// avoid merging it with the right (uncompressed) page
return(null);
}
Debug.Assert(page.IsCompressed == false);
minKeys = sibling.IsBranch ? 2 : 1; // branch must have at least 2 keys
if (sibling.UseMoreSizeThan(_tx.DataPager.PageMinSpace) &&
sibling.NumberOfEntries > minKeys)
{
// neighbor is over the min size and has enough key, can move just one key to the current page
if (page.IsBranch)
{
MoveBranchNode(parentPage, sibling, page);
}
else
{
MoveLeafNode(parentPage, sibling, page);
}
return(parentPage);
}
if (page.LastSearchPosition == 0) // this is the right page, merge left
{
if (TryMergePages(parentPage, sibling, page) == false)
{
return(null);
}
}
else // this is the left page, merge right
{
if (TryMergePages(parentPage, page, sibling) == false)
{
return(null);
}
}
return(parentPage);
}
}