.

wcfs/internal/xbtree/δbtail.go

@@ -43,18 +43,12 @@ const debugΔBtail = false
 // It semantically consists of
 //
 //	[]δB			; rev ∈ (tail, head]
-//	atTail					XXX no need (see vvv)
 //
 // where δB represents a change in BTrees space
 //
 //	δB:
 //		.rev↑
-//		{} root -> {}(key, δvalue)	XXX was value
-//
-// and atTail keeps set of k/v @tail for keys changed in (tail, head]
-//
-//	atTail:					XXX no need for atTail as we have δvalue.Old
-//		{} root -> {}(key, value)
+//		{} root -> {}(key, δvalue)
 //
 // It covers only changes to keys from tracked subset of BTrees parts.
 // In particular a key that was not explicitly requested to be tracked, even if
@@ -62,7 +56,7 @@ const debugΔBtail = false
 //
 // ΔBtail provides the following operations:
 //
-//   .Track(path)		- start tracking tree nodes and keys; root=path[0], keys=path[-1].keys  XXX keys not correct - e.g. track missing key
+//   .Track(path)		- start tracking tree nodes and keys; root=path[0], keys=path[-1].(lo,hi]
 //
 //   .Update(δZ) -> δB				- update BTree δ tail given raw ZODB changes
 //   .ForgetPast(revCut)			- forget changes past revCut
@@ -80,7 +74,7 @@ const debugΔBtail = false
 //
 // XXX incremental; not full coverage
 //
-// ΔBtail is not safe for concurrent access.
+// ΔBtail is not safe for concurrent access.	XXX rework
 // XXX -> multiple readers / single writer?
 //
 // See also zodb.ΔTail
@@ -775,7 +769,8 @@ func (δTtail *ΔTtail) forgetPast(revCut zodb.Tid) {
 //
 // XXX root -> Oid ?
 func (δBtail *ΔBtail) GetAt(ctx context.Context, root *Tree, key Key, at zodb.Tid) (value Value, ok bool, rev zodb.Tid, revExact bool, err error) {
-	defer xerr.Contextf(&err, "δBtail: root<%s>: get %d @%s", root.POid(), key, at)
+	rootOid := root.POid()
+	defer xerr.Contextf(&err, "δBtail: root<%s>: get %d @%s", rootOid, key, at)
 	// XXX key not tracked		-> panic
 	// XXX at not ∈ (tail, head]	-> panic
 
@@ -786,14 +781,14 @@ func (δBtail *ΔBtail) GetAt(ctx context.Context, root *Tree, key Key, at zodb.
 		panicf("δBtail: root.at (@%s)  !=  head (@%s)", rootAt, δBtail.Head())
 	}
 
-	err = δBtail.rebuild1IfNeeded(root.POid())
+	err = δBtail.rebuild1IfNeeded(rootOid)
 	if err != nil {
 		return
 	}
 
-	δTtail := δBtail.vδTbyRoot[root.POid()]
+	δTtail := δBtail.vδTbyRoot[rootOid]
 	if δTtail == nil {
-		panicf("δBtail: root<%s> not tracked", root.POid())
+		panicf("δBtail: root<%s> not tracked", rootOid)
 	}
 
 	// XXX -> index lastXXXOf(key) | linear scan ↓ looking for change <= at
@@ -823,12 +818,12 @@ func (δBtail *ΔBtail) GetAt(ctx context.Context, root *Tree, key Key, at zodb.
 		return
 	}
 
-	// key not in history tail at all.
-	// use @head[key]
-
-	// XXX can we avoid requiring live root?
-	// @tail[key] is not present - key was not changing in (tail, head].
-	// since at ∈ (tail, head] we can use @head[key] as the result
+	// δBtail[key] is not present - key was not changing in (tail, head].
+	// since at ∈ (tail, head] as the result we can use @rev[key] for any
+	// rev ∈ (tail, head].
+	//
+	// XXX can we avoid requiring live root? (think again afresh)
+	// XXX -> move handling of "key not in δBtail -> to δFtail.LastBlkRev"
 	xvalue, ok, err := root.Get(ctx, key)
 	if !ok {
 		value = VDEL