nimbus-eth1/nimbus/db/aristo/aristo_merge.nim

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Nim

# nimbus-eth1
# Copyright (c) 2021 Status Research & Development GmbH
# Licensed under either of
# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
# http://www.apache.org/licenses/LICENSE-2.0)
# * MIT license ([LICENSE-MIT](LICENSE-MIT) or
# http://opensource.org/licenses/MIT)
# at your option. This file may not be copied, modified, or distributed
# except according to those terms.
## Aristo DB -- Patricia Trie builder, raw node insertion
## ======================================================
##
## This module merges `HashID` values as hexary lookup paths into the
## `Patricia Trie`. When changing vertices (aka nodes without Merkle hashes),
## associated (but separated) Merkle hashes will be deleted unless locked.
## Instead of deleting locked hashes error handling is applied.
##
## Also, nodes (vertices plus merkle hashes) can be added which is needed for
## boundary proofing after `snap/1` download. The vertices are split from the
## nodes and stored as-is on the table holding `Patricia Trie` entries. The
## hashes are stored iin a separate table and the vertices are labelled
## `locked`.
{.push raises: [].}
import
std/[algorithm, sequtils, strutils, sets, tables],
chronicles,
eth/[common, trie/nibbles],
stew/results,
../../sync/protocol,
"."/[aristo_desc, aristo_get, aristo_hike, aristo_path, aristo_transcode,
aristo_vid]
logScope:
topics = "aristo-merge"
type
LeafTiePayload* = object
## Generalised key-value pair for a sub-trie. The main trie is the
## sub-trie with `root=VertexID(1)`.
leafTie*: LeafTie ## Full `Patricia Trie` path root-to-leaf
payload*: PayloadRef ## Leaf data payload
# ------------------------------------------------------------------------------
# Private getters & setters
# ------------------------------------------------------------------------------
proc xPfx(vtx: VertexRef): NibblesSeq =
case vtx.vType:
of Leaf:
return vtx.lPfx
of Extension:
return vtx.ePfx
of Branch:
doAssert vtx.vType != Branch # Ooops
proc `xPfx=`(vtx: VertexRef, val: NibblesSeq) =
case vtx.vType:
of Leaf:
vtx.lPfx = val
of Extension:
vtx.ePfx = val
of Branch:
doAssert vtx.vType != Branch # Ooops
# ------------------------------------------------------------------------------
# Private helpers
# ------------------------------------------------------------------------------
proc clearMerkleKeys(
db: AristoDbRef; # Database, top layer
hike: Hike; # Implied vertex IDs to clear hashes for
vid: VertexID; # Additionall vertex IDs to clear
) =
for vid in hike.legs.mapIt(it.wp.vid) & @[vid]:
let lbl = db.top.kMap.getOrVoid vid
if lbl.isValid:
db.top.kMap.del vid
db.top.pAmk.del lbl
elif db.getKeyBackend(vid).isOK:
# Register for deleting on backend
db.top.kMap[vid] = VOID_HASH_LABEL
db.top.pAmk.del lbl
# -----------
proc insertBranch(
db: AristoDbRef; # Database, top layer
hike: Hike; # Current state
linkID: VertexID; # Vertex ID to insert
linkVtx: VertexRef; # Vertex to insert
payload: PayloadRef; # Leaf data payload
): Hike =
##
## Insert `Extension->Branch` vertex chain or just a `Branch` vertex
##
## ... --(linkID)--> <linkVtx>
##
## <-- immutable --> <---- mutable ----> ..
##
## will become either
##
## --(linkID)-->
## <extVtx> --(local1)-->
## <forkVtx>[linkInx] --(local2)--> <linkVtx*>
## [leafInx] --(local3)--> <leafVtx>
##
## or in case that there is no common prefix
##
## --(linkID)-->
## <forkVtx>[linkInx] --(local2)--> <linkVtx*>
## [leafInx] --(local3)--> <leafVtx>
##
## *) vertex was slightly modified or removed if obsolete `Extension`
##
let n = linkVtx.xPfx.sharedPrefixLen hike.tail
# Verify minimum requirements
if hike.tail.len == n:
# Should have been tackeld by `hikeUp()`, already
return Hike(error: MergeLeafGarbledHike)
if linkVtx.xPfx.len == n:
return Hike(error: MergeBrLinkVtxPfxTooShort)
# Provide and install `forkVtx`
let
forkVtx = VertexRef(vType: Branch)
linkInx = linkVtx.xPfx[n]
leafInx = hike.tail[n]
var
leafLeg = Leg(nibble: -1)
# Install `forkVtx`
block:
# Clear Merkle hashes (aka hash keys) unless proof mode.
if db.top.pPrf.len == 0:
db.clearMerkleKeys(hike, linkID)
elif linkID in db.top.pPrf:
return Hike(error: MergeNonBranchProofModeLock)
if linkVtx.vType == Leaf:
# Update vertex path lookup
let
path = hike.legsTo(NibblesSeq) & linkVtx.lPfx
rc = path.pathToTag()
if rc.isErr:
debug "Branch link leaf path garbled", linkID, path
return Hike(error: MergeBrLinkLeafGarbled)
let
local = db.vidFetch(pristine = true)
lty = LeafTie(root: hike.root, path: rc.value)
db.top.lTab[lty] = local # update leaf path lookup cache
db.top.sTab[local] = linkVtx
linkVtx.lPfx = linkVtx.lPfx.slice(1+n)
forkVtx.bVid[linkInx] = local
elif linkVtx.ePfx.len == n + 1:
# This extension `linkVtx` becomes obsolete
forkVtx.bVid[linkInx] = linkVtx.eVid
else:
let local = db.vidFetch
db.top.sTab[local] = linkVtx
linkVtx.ePfx = linkVtx.ePfx.slice(1+n)
forkVtx.bVid[linkInx] = local
block:
let local = db.vidFetch(pristine = true)
forkVtx.bVid[leafInx] = local
leafLeg.wp.vid = local
leafLeg.wp.vtx = VertexRef(
vType: Leaf,
lPfx: hike.tail.slice(1+n),
lData: payload)
db.top.sTab[local] = leafLeg.wp.vtx
# Update branch leg, ready to append more legs
result = Hike(root: hike.root, legs: hike.legs)
# Update in-beween glue linking `branch --[..]--> forkVtx`
if 0 < n:
let extVtx = VertexRef(
vType: Extension,
ePfx: hike.tail.slice(0,n),
eVid: db.vidFetch)
db.top.sTab[linkID] = extVtx
result.legs.add Leg(
nibble: -1,
wp: VidVtxPair(
vid: linkID,
vtx: extVtx))
db.top.sTab[extVtx.eVid] = forkVtx
result.legs.add Leg(
nibble: leafInx.int8,
wp: VidVtxPair(
vid: extVtx.eVid,
vtx: forkVtx))
else:
db.top.sTab[linkID] = forkVtx
result.legs.add Leg(
nibble: leafInx.int8,
wp: VidVtxPair(
vid: linkID,
vtx: forkVtx))
result.legs.add leafLeg
proc concatBranchAndLeaf(
db: AristoDbRef; # Database, top layer
hike: Hike; # Path top has a `Branch` vertex
brVid: VertexID; # Branch vertex ID from from `Hike` top
brVtx: VertexRef; # Branch vertex, linked to from `Hike`
payload: PayloadRef; # Leaf data payload
): Hike =
## Append argument branch vertex passed as argument `(brID,brVtx)` and then
## a `Leaf` vertex derived from the argument `payload`.
##
if hike.tail.len == 0:
return Hike(error: MergeBranchGarbledTail)
let nibble = hike.tail[0].int8
if brVtx.bVid[nibble].isValid:
return Hike(error: MergeRootBranchLinkBusy)
# Clear Merkle hashes (aka hash keys) unless proof mode.
if db.top.pPrf.len == 0:
db.clearMerkleKeys(hike, brVid)
elif brVid in db.top.pPrf:
return Hike(error: MergeBranchProofModeLock) # Ooops
# Append branch vertex
result = Hike(root: hike.root, legs: hike.legs)
result.legs.add Leg(wp: VidVtxPair(vtx: brVtx, vid: brVid), nibble: nibble)
# Append leaf vertex
let
vid = db.vidFetch(pristine = true)
vtx = VertexRef(
vType: Leaf,
lPfx: hike.tail.slice(1),
lData: payload)
brVtx.bVid[nibble] = vid
db.top.sTab[brVid] = brVtx
db.top.sTab[vid] = vtx
result.legs.add Leg(wp: VidVtxPair(vtx: vtx, vid: vid), nibble: -1)
# ------------------------------------------------------------------------------
# Private functions: add Particia Trie leaf vertex
# ------------------------------------------------------------------------------
proc topIsBranchAddLeaf(
db: AristoDbRef; # Database, top layer
hike: Hike; # Path top has a `Branch` vertex
payload: PayloadRef; # Leaf data payload
): Hike =
## Append a `Leaf` vertex derived from the argument `payload` after the top
## leg of the `hike` argument which is assumend to refert to a `Branch`
## vertex. If successful, the function returns the updated `hike` trail.
if hike.tail.len == 0:
return Hike(error: MergeBranchGarbledTail)
let nibble = hike.legs[^1].nibble
if nibble < 0:
return Hike(error: MergeBranchGarbledNibble)
let
branch = hike.legs[^1].wp.vtx
linkID = branch.bVid[nibble]
linkVtx = db.getVtx linkID
if not linkVtx.isValid:
#
# .. <branch>[nibble] --(linkID)--> nil
#
# <-------- immutable ------------> <---- mutable ----> ..
#
if db.top.pPrf.len == 0:
# Not much else that can be done here
debug "Dangling leaf link, reused", branch=hike.legs[^1].wp.vid,
nibble, linkID, leafPfx=hike.tail
# Reuse placeholder entry in table
let vtx = VertexRef(
vType: Leaf,
lPfx: hike.tail,
lData: payload)
db.top.sTab[linkID] = vtx
result = Hike(root: hike.root, legs: hike.legs)
result.legs.add Leg(wp: VidVtxPair(vid: linkID, vtx: vtx), nibble: -1)
return
if linkVtx.vType == Branch:
# Slot link to a branch vertex should be handled by `hikeUp()`
#
# .. <branch>[nibble] --(linkID)--> <linkVtx>[]
#
# <-------- immutable ------------> <---- mutable ----> ..
#
return db.concatBranchAndLeaf(hike, linkID, linkVtx, payload)
db.insertBranch(hike, linkID, linkVtx, payload)
proc topIsExtAddLeaf(
db: AristoDbRef; # Database, top layer
hike: Hike; # Path top has an `Extension` vertex
payload: PayloadRef; # Leaf data payload
): Hike =
## Append a `Leaf` vertex derived from the argument `payload` after the top
## leg of the `hike` argument which is assumend to refert to a `Extension`
## vertex. If successful, the function returns the
## updated `hike` trail.
let
extVtx = hike.legs[^1].wp.vtx
extVid = hike.legs[^1].wp.vid
brVid = extVtx.eVid
brVtx = db.getVtx brVid
result = Hike(root: hike.root, legs: hike.legs)
if not brVtx.isValid:
# Blind vertex, promote to leaf vertex.
#
# --(extVid)--> <extVtx> --(brVid)--> nil
#
# <-------- immutable -------------->
#
let vtx = VertexRef(
vType: Leaf,
lPfx: extVtx.ePfx & hike.tail,
lData: payload)
db.top.sTab[extVid] = vtx
result.legs[^1].wp.vtx = vtx
elif brVtx.vType != Branch:
return Hike(error: MergeBranchRootExpected)
else:
let
nibble = hike.tail[0].int8
linkID = brVtx.bVid[nibble]
#
# Required
#
# --(extVid)--> <extVtx> --(brVid)--> <brVtx>[nibble] --(linkID)--> nil
#
# <-------- immutable --------------> <-------- mutable ----------> ..
#
if linkID.isValid:
return Hike(error: MergeRootBranchLinkBusy)
# Clear Merkle hashes (aka hash keys) unless proof mode
if db.top.pPrf.len == 0:
db.clearMerkleKeys(hike, brVid)
elif brVid in db.top.pPrf:
return Hike(error: MergeBranchProofModeLock)
let
vid = db.vidFetch(pristine = true)
vtx = VertexRef(
vType: Leaf,
lPfx: hike.tail.slice(1),
lData: payload)
brVtx.bVid[nibble] = vid
db.top.sTab[brVid] = brVtx
db.top.sTab[vid] = vtx
result.legs.add Leg(wp: VidVtxPair(vtx: brVtx, vid: brVid), nibble: nibble)
result.legs.add Leg(wp: VidVtxPair(vtx: vtx, vid: vid), nibble: -1)
proc topIsEmptyAddLeaf(
db: AristoDbRef; # Database, top layer
hike: Hike; # No path legs
rootVtx: VertexRef; # Root vertex
payload: PayloadRef; # Leaf data payload
): Hike =
## Append a `Leaf` vertex derived from the argument `payload` after the
## argument vertex `rootVtx` and append both the empty arguent `hike`.
if rootVtx.vType == Branch:
let nibble = hike.tail[0].int8
if rootVtx.bVid[nibble].isValid:
return Hike(error: MergeRootBranchLinkBusy)
# Clear Merkle hashes (aka hash keys) unless proof mode
if db.top.pPrf.len == 0:
db.clearMerkleKeys(hike, hike.root)
elif hike.root in db.top.pPrf:
return Hike(error: MergeBranchProofModeLock)
let
leafVid = db.vidFetch(pristine = true)
leafVtx = VertexRef(
vType: Leaf,
lPfx: hike.tail.slice(1),
lData: payload)
rootVtx.bVid[nibble] = leafVid
db.top.sTab[hike.root] = rootVtx
db.top.sTab[leafVid] = leafVtx
return Hike(
root: hike.root,
legs: @[Leg(wp: VidVtxPair(vtx: rootVtx, vid: hike.root), nibble: nibble),
Leg(wp: VidVtxPair(vtx: leafVtx, vid: leafVid), nibble: -1)])
db.insertBranch(hike, hike.root, rootVtx, payload)
proc updatePayload(
db: AristoDbRef; # Database, top layer
hike: Hike; # No path legs
leaf: LeafTiePayload; # Leaf data and payload
): Hike =
## Update leaf vertex if payloads differ
result = hike
let vtx = result.legs[^1].wp.vtx
# Update payloads if they differ
if vtx.lData != leaf.payload:
let vid = result.legs[^1].wp.vid
vtx.lData = leaf.payload
db.top.sTab[vid] = vtx
db.top.lTab[leaf.leafTie] = vid
db.clearMerkleKeys(result, vid)
# ------------------------------------------------------------------------------
# Private functions: add Merkle proof node
# ------------------------------------------------------------------------------
proc mergeNodeImpl(
db: AristoDbRef; # Database, top layer
hashKey: HashKey; # Merkel hash of node
node: NodeRef; # Node derived from RLP representation
rootVid: VertexID; # Current sub-trie
): Result[VertexID,AristoError] =
## The function merges the argument hash key `hashKey` as expanded from the
## node RLP representation into the `Aristo Trie` database. The vertex is
## split off from the node and stored separately. So are the Merkle hashes.
## The vertex is labelled `locked`.
##
## The `node` argument is *not* checked, whether the vertex IDs have been
## allocated, already. If the node comes straight from the `decode()` RLP
## decoder as expected, these vertex IDs will be all zero.
##
if node.error != AristoError(0):
return err(node.error)
if not rootVid.isValid:
return err(MergeRootKeyInvalid)
# Verify `hashKey`
if not hashKey.isValid:
return err(MergeHashKeyInvalid)
# Make sure that the `vid<->hashLbl` reverse mapping has been cached,
# already. This is provided for if the `nodes` are processed in the right
# order `root->.. ->leaf`.
let
hashLbl = HashLabel(root: rootVid, key: hashKey)
vid = db.top.pAmk.getOrVoid hashLbl
if not vid.isValid:
return err(MergeRevVidMustHaveBeenCached)
let lbl = db.top.kMap.getOrVoid vid
if lbl == hashLbl:
if db.top.sTab.hasKey vid:
# This is tyically considered OK
return err(MergeHashKeyCachedAlready)
# Otherwise proceed
elif lbl.isValid:
# Different key assigned => error
return err(MergeHashKeyDiffersFromCached)
let (vtx, hasVtx) = block:
let vty = db.getVtx vid
if vty.isValid:
(vty, true)
else:
(node.to(VertexRef), false)
# The `vertexID <-> hashLabel` mappings need to be set up now (if any)
case node.vType:
of Leaf:
discard
of Extension:
if node.key[0].isValid:
let eLbl = HashLabel(root: rootVid, key: node.key[0])
if hasVtx:
if not vtx.eVid.isValid:
return err(MergeNodeVtxDiffersFromExisting)
db.top.pAmk[eLbl] = vtx.eVid
else:
let eVid = db.top.pAmk.getOrVoid eLbl
if eVid.isValid:
vtx.eVid = eVid
else:
vtx.eVid = db.vidAttach eLbl
of Branch:
for n in 0..15:
if node.key[n].isValid:
let bLbl = HashLabel(root: rootVid, key: node.key[n])
if hasVtx:
if not vtx.bVid[n].isValid:
return err(MergeNodeVtxDiffersFromExisting)
db.top.pAmk[bLbl] = vtx.bVid[n]
else:
let bVid = db.top.pAmk.getOrVoid bLbl
if bVid.isValid:
vtx.bVid[n] = bVid
else:
vtx.bVid[n] = db.vidAttach bLbl
db.top.pPrf.incl vid
if hasVtx:
let key = db.getKey vid
if key != hashKey:
db.top.sTab[vid] = vtx
else:
db.top.sTab[vid] = vtx
ok vid
# ------------------------------------------------------------------------------
# Public functions
# ------------------------------------------------------------------------------
proc merge*(
db: AristoDbRef; # Database, top layer
leaf: LeafTiePayload; # Leaf item to add to the database
): Hike =
## Merge the argument `leaf` key-value-pair into the top level vertex table
## of the database `db`. The field `pathKey` of the `leaf` argument is used
## to index the leaf vertex on the `Patricia Trie`. The field `payload` is
## stored with the leaf vertex in the database unless the leaf vertex exists
## already.
##
# Check whether the leaf is on the database and payloads match
var haveLeafOk = false
block:
let vid = db.top.lTab.getOrVoid leaf.leafTie
if vid.isValid:
let vtx = db.getVtx vid
if vtx.isValid and vtx.lData == leaf.payload:
haveLeafOk = true
if haveLeafOk:
result.error = MergeLeafPathCachedAlready
else:
let hike = leaf.leafTie.hikeUp(db)
if 0 < hike.legs.len:
case hike.legs[^1].wp.vtx.vType:
of Branch:
result = db.topIsBranchAddLeaf(hike, leaf.payload)
of Leaf:
if 0 < hike.tail.len: # `Leaf` vertex problem?
return Hike(error: MergeLeafGarbledHike)
result = db.updatePayload(hike, leaf)
of Extension:
result = db.topIsExtAddLeaf(hike, leaf.payload)
else:
# Empty hike
let rootVtx = db.getVtx hike.root
if rootVtx.isValid:
result = db.topIsEmptyAddLeaf(hike,rootVtx,leaf.payload)
else:
# Bootstrap for existing root ID
let wp = VidVtxPair(
vid: hike.root,
vtx: VertexRef(
vType: Leaf,
lPfx: leaf.leafTie.path.to(NibblesSeq),
lData: leaf.payload))
db.top.sTab[wp.vid] = wp.vtx
result = Hike(root: wp.vid, legs: @[Leg(wp: wp, nibble: -1)])
# Double check the result until the code is more reliable
block:
let rc = result.to(NibblesSeq).pathToKey
if rc.isErr or rc.value != leaf.leafTie.path.to(HashKey):
result.error = MergeAssemblyFailed # Ooops
# Update leaf acccess cache
if result.error == AristoError(0):
db.top.lTab[leaf.leafTie] = result.legs[^1].wp.vid
# End else (1st level)
proc merge*(
db: AristoDbRef; # Database, top layer
leafs: openArray[LeafTiePayload]; # Leaf items to add to the database
): tuple[merged: int, dups: int, error: AristoError] =
## Variant of `merge()` for leaf lists.
var (merged, dups) = (0, 0)
for n,w in leafs:
let hike = db.merge w
if hike.error == AristoError(0):
merged.inc
elif hike.error == MergeLeafPathCachedAlready:
dups.inc
else:
return (n,dups,hike.error)
(merged, dups, AristoError(0))
# ---------------------
proc merge*(
db: AristoDbRef; # Database, top layer
proof: openArray[SnapProof]; # RLP encoded node records
rootVid: VertexID; # Current sub-trie
): tuple[merged: int, dups: int, error: AristoError]
{.gcsafe, raises: [RlpError].} =
## The function merges the argument `proof` list of RLP encoded node records
## into the `Aristo Trie` database. This function is intended to be used with
## the proof nodes as returened by `snap/1` messages.
##
if not rootVid.isValid:
return (0,0,MergeRootVidInvalid)
let rootKey = db.getKey rootVid
if not rootKey.isValid:
return (0,0,MergeRootKeyInvalid)
# Expand and collect hash keys and nodes
var nodeTab: Table[HashKey,NodeRef]
for w in proof:
let
key = w.Blob.digestTo(HashKey)
node = w.Blob.decode(NodeRef)
nodeTab[key] = node
# Create a table with back links
var
backLink: Table[HashKey,HashKey]
blindNodes: HashSet[HashKey]
for (key,node) in nodeTab.pairs:
case node.vType:
of Leaf:
blindNodes.incl key
of Extension:
if nodeTab.hasKey node.key[0]:
backLink[node.key[0]] = key
else:
blindNodes.incl key
of Branch:
var isBlind = true
for n in 0 .. 15:
if nodeTab.hasKey node.key[n]:
isBlind = false
backLink[node.key[n]] = key
if isBlind:
blindNodes.incl key
# Run over blind nodes and build chains from a blind/bottom level node up
# to the root node. Select only chains that end up at the pre-defined root
# node.
var chains: seq[seq[HashKey]]
for w in blindNodes:
# Build a chain of nodes up to the root node
var
chain: seq[HashKey]
nodeKey = w
while nodeKey.isValid and nodeTab.hasKey nodeKey:
chain.add nodeKey
nodeKey = backLink.getOrDefault(nodeKey, VOID_HASH_KEY)
if 0 < chain.len and chain[^1] == rootKey:
chains.add chain
# Make sure that the reverse lookup for the root vertex label is available.
block:
let
lbl = HashLabel(root: rootVid, key: rootKey)
vid = db.top.pAmk.getOrVoid lbl
if not vid.isvalid:
db.top.pAmk[lbl] = rootVid
# Process over chains in reverse mode starting with the root node. This
# allows the algorithm to find existing nodes on the backend.
var
seen: HashSet[HashKey]
(merged, dups) = (0, 0)
# Process the root ID which is common to all chains
for chain in chains:
for key in chain.reversed:
if key in seen:
discard
else:
seen.incl key
let
node = nodeTab.getOrDefault(key, NodeRef(nil))
rc = db.mergeNodeImpl(key, node, rootVid)
if rc.isOK:
merged.inc
elif rc.error == MergeHashKeyCachedAlready:
dups.inc
else:
return (merged, dups, rc.error)
(merged, dups, AristoError(0))
proc merge*(
db: AristoDbRef; # Database, top layer
rootKey: HashKey; # Merkle hash for root
rootVid = VertexID(0) # Optionally, force root vertex ID
): Result[VertexID,AristoError] =
## Set up a `rootKey` associated with a vertex ID.
##
## If argument `rootVid` is unset (defaults to `VertexID(0)`) then the main
## trie is tested for `VertexID(1)`. If assigned with a different Merkle key
## already, a new vertex ID is created and the argument root key is assigned
## to this vertex ID.
##
## If the argument `rootVid` is set (to a value different from `VertexID(0)`),
## then a sub-trie with root `rootVid` is checked for. If it exists with a
## diffent root key assigned, then an error is returned. Otherwise a new
## vertex ID is created and the argument root key is assigned.
##
## Upon successful return, the vertex ID assigned to the root key is returned.
##
if not rootKey.isValid:
return err(MergeRootKeyInvalid)
if rootVid.isValid and rootVid != VertexID(1):
let key = db.getKey rootVid
if key == rootKey:
return ok rootVid
if not key.isValid:
db.vidAttach(HashLabel(root: rootVid, key: rootKey), rootVid)
return ok rootVid
else:
let key = db.getKey VertexID(1)
if key == rootKey:
return ok VertexID(1)
# Otherwise assign unless valid
if not key.isValid:
db.vidAttach(HashLabel(root: VertexID(1), key: rootKey), VertexID(1))
return ok VertexID(1)
# Create and assign a new root key
if not rootVid.isValid:
return ok db.vidRoot(rootKey)
err(MergeRootKeyDiffersForVid)
# ------------------------------------------------------------------------------
# End
# ------------------------------------------------------------------------------