/// <summary>
/// Create a new index and returns head page address (skip list)
/// </summary>
public CollectionIndex CreateIndex(string name, string expr, bool unique)
{
// get how many butes needed fore each head/tail (both has same size)
var bytesLength = IndexNode.GetNodeLength(MAX_LEVEL_LENGTH, BsonValue.MinValue, out var keyLength);
// get a new empty page (each index contains your own linked nodes)
var indexPage = _snapshot.NewPage <IndexPage>();
// create index ref
var index = _snapshot.CollectionPage.InsertCollectionIndex(name, expr, unique);
// insert head/tail nodes
var head = indexPage.InsertIndexNode(index.Slot, MAX_LEVEL_LENGTH, BsonValue.MinValue, PageAddress.Empty, bytesLength);
var tail = indexPage.InsertIndexNode(index.Slot, MAX_LEVEL_LENGTH, BsonValue.MaxValue, PageAddress.Empty, bytesLength);
// link head-to-tail with double link list in first level
head.SetNext(0, tail.Position);
tail.SetPrev(0, head.Position);
// add this new page in free list (slot 0)
index.FreeIndexPageList = indexPage.PageID;
indexPage.PageListSlot = 0;
index.Head = head.Position;
index.Tail = tail.Position;
return(index);
}
/// <summary>
/// Create a new index and returns head page address (skip list)
/// </summary>
public CollectionIndex CreateIndex(string name, string expr, bool unique)
{
// get how many butes needed fore each head/tail (both has same size)
var bytesLength = IndexNode.GetNodeLength(MAX_LEVEL_LENGTH, BsonValue.MinValue, out var keyLength);
// get a free index page for head note (x2 for head + tail)
var indexPage = _snapshot.GetFreePage <IndexPage>(bytesLength * 2);
// create index ref
var index = _snapshot.CollectionPage.InsertCollectionIndex(name, expr, unique);
// insert head/tail nodes
var head = indexPage.InsertIndexNode(index.Slot, MAX_LEVEL_LENGTH, BsonValue.MinValue, PageAddress.Empty, bytesLength);
var tail = indexPage.InsertIndexNode(index.Slot, MAX_LEVEL_LENGTH, BsonValue.MaxValue, PageAddress.Empty, bytesLength);
// link head-to-tail with double link list in first level
head.SetNext(0, tail.Position);
tail.SetPrev(0, head.Position);
index.Head = head.Position;
index.Tail = tail.Position;
return(index);
}
/// <summary>
/// Insert a new node index inside an collection index.
/// </summary>
private IndexNode AddNode(CollectionIndex index, BsonValue key, PageAddress dataBlock, byte level, IndexNode last)
{
// get a free index page for head note
var bytesLength = IndexNode.GetNodeLength(level, key, out var keyLength);
// test for index key maxlength
if (keyLength > MAX_INDEX_KEY_LENGTH)
{
throw LiteException.InvalidIndexKey($"Index key must be less than {MAX_INDEX_KEY_LENGTH} bytes.");
}
var indexPage = _snapshot.GetFreeIndexPage(bytesLength, ref index.FreeIndexPageList);
// create node in buffer
var node = indexPage.InsertIndexNode(index.Slot, level, key, dataBlock, bytesLength);
// now, let's link my index node on right place
var cur = this.GetNode(index.Head);
// using as cache last
IndexNode cache = null;
// scan from top left
for (int i = index.MaxLevel - 1; i >= 0; i--)
{
// get cache for last node
cache = cache != null && cache.Position == cur.Next[i] ? cache : this.GetNode(cur.Next[i]);
// for(; <while_not_this>; <do_this>) { ... }
for (; cur.Next[i].IsEmpty == false; cur = cache)
{
// get cache for last node
cache = cache != null && cache.Position == cur.Next[i] ? cache : this.GetNode(cur.Next[i]);
// read next node to compare
var diff = cache.Key.CompareTo(key, _collation);
// if unique and diff = 0, throw index exception (must rollback transaction - others nodes can be dirty)
if (diff == 0 && index.Unique)
{
throw LiteException.IndexDuplicateKey(index.Name, key);
}
if (diff == 1)
{
break;
}
}
if (i <= (level - 1)) // level == length
{
// cur = current (immediately before - prev)
// node = new inserted node
// next = next node (where cur is pointing)
node.SetNext((byte)i, cur.Next[i]);
node.SetPrev((byte)i, cur.Position);
cur.SetNext((byte)i, node.Position);
var next = this.GetNode(node.Next[i]);
if (next != null)
{
next.SetPrev((byte)i, node.Position);
}
}
}
// if last node exists, create a double link list
if (last != null)
{
ENSURE(last.NextNode == PageAddress.Empty, "last index node must point to null");
last.SetNextNode(node.Position);
}
// fix page position in free list slot
_snapshot.AddOrRemoveFreeIndexList(node.Page, ref index.FreeIndexPageList);
return(node);
}