Sync

wcfs/internal/xbtree/δbtail.go

@@ -82,15 +82,23 @@ type Tree   = btree.LOBTree
 type Bucket = btree.LOBucket
 type Node   = btree.LONode
 type Key    = int64
+type Value  = zodb.Oid // XXX assumes key points to IPersistent
 
 // ΔTail represents tail of revisional changes to BTrees.
 //
-// It semantically consists of
+// It covers changes to keys from tracked subset of BTrees parts and
+// semantically consists of
 //
-//	[](rev↑, [](root, []key))	; rev ∈ (tail, head]
+//	# k/v change history		; rev ∈ (tail, head]
+//	[](rev↑,
+//	    [](root,
+//	        {}(key, value)))
 //
-// and covers changes to tracked subsets of BTrees. A tree subset becomes
-// tracked via Track(path) request.
+//	# set of k/v @tail for keys that are not changed in (tail, head].
+//	{} root ->
+//		{}(key, value)
+//
+// A tree nodes become tracked via Track(path) request.
 //
 // An example for tracked set is a set of visited BTree paths.
 // There is no requirement that tracked set belongs to only one single BTree.
@@ -105,7 +113,9 @@ type Key    = int64
 type ΔTail struct {
 	δBtail []ΔRevEntry // BTree changes; Covers keys ∈ tracket subset
 	δZtail *zodb.ΔTail // raw ZODB changes; Kept to rebuild δBtail after new Track
-//	head   zodb.Tid    // δBtail currently has coverage till head], δZtail can have more
+
+	// {} root -> {}k/v @tail for keys that are not changed in (tail, head].
+	atTail map[*Tree]map[Key]Value
 
 	// XXX or ask client provide db on every call?
 	db     *zodb.DB    // to open connections to load new/old tree|buckets