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wcfs/internal/δbtree/δbtail.go

+// Copyright (C) 2019  Nexedi SA and Contributors.
+//                     Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+package δbtree
+// XXX -> another package?
+
+// ΔBTail reprsents tail of revisional changes to BTrees.
+//
+// It semantically consists of
+//
+//	[](rev↑, (tree, []key))		; rev ∈ (tail, head]
+//
+// and *partially* covers changes to BTrees.
+//
+// XXX δB can convert δZ to btree changes, but only at least for δZ's objects
+// that ∈ BTree subgraphs that were explicitly requested to be tracked by δB.
+//
+// XXX incremental; not full coverage
+type ΔBTail struct {
+	//at // = head
+	δZtail *zodb.ΔTail
+
+	// XXX or ask client provide db on every call?
+	db     *zodb.DB    // to open connections to load new/old tree|buckets
+
+	// root index: BTree|Bucket -> top tree element.
+	// XXX represent root by oid instead of live object?
+	rootIdx map[zodb.Oid]SetTree // oid -> {} roots
+}
+
+// XXX path is at @at state.
+// XXX objects in path must be with .PJar().At() == .head
+// XXX path -> []oid ?
+func (δb *ΔBTail) Track(path []zodb.IPersistent) {	// XXX Tree|Bucket; path[0] = root
+	// XXX
+}
+
+// Update updates δB with per-object level ZODB changes.
+//
+// XXX text ...
+// XXX -> Append? -> Invalidate?
+// XXX -> DiffTo ?
+func (δB *ΔBTail) Update(δZ *zodb.EventCommit) {
+/*
+	.δZtail += δZ
+	δbZ = {}
+	for δ in δZ:
+		.rootIdx[δ]:
+			ø	-> nothing
+			root	-> δbZ[root] += δ
+
+	if δbZ == ø:
+		return
+
+	zconnNew = db.Open(δZ.rev)
+
+	for root, δZ in δbZ:
+		toposort(δZ)
+		for δ in δZ:
+			T  | B  = zconn.Get(δ)		// XXX .zconn must be at .head and active
+			T' | B' = zconnNew.Get(δ)
+			diff(T, T')
+			diff(B, B')
+			...
+
+	-> [] of (root, []key)
+*/
+}