graph/db: remove ChannelGraph cacheMu

We remove the mutex that was previously held between DB calls and calls
that update the graphCache. This is done so that the underlying DB calls
can make use of any batch requests which they currently cannot since the
mutex prevents multiple requests from calling the methods at once.

The reason the cacheMu was originally added here was during a code
refactor that moved the `graphCache` out of the `KVStore` and into the
`ChannelGraph` and the aim was then to have a best effort way of
ensuring that updates to the DB and updates to the graphCache were as
consistent/atomic as possible.

Author: ellemouton

graph/db/graph.go

@@ -41,11 +41,6 @@ type ChannelGraph struct {
 	started atomic.Bool
 	stopped atomic.Bool
 
-	// cacheMu guards any writes to the graphCache. It should be held
-	// across the DB write call and the graphCache update to make the
-	// two updates as atomic as possible.
-	cacheMu sync.Mutex
-
 	graphCache *GraphCache
 
 	*KVStore
@@ -283,9 +278,6 @@ func (c *ChannelGraph) ForEachNodeCached(cb func(node route.Vertex,
 func (c *ChannelGraph) AddLightningNode(node *models.LightningNode,
 	op ...batch.SchedulerOption) error {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	err := c.KVStore.AddLightningNode(node, op...)
 	if err != nil {
 		return err
@@ -309,9 +301,6 @@ func (c *ChannelGraph) AddLightningNode(node *models.LightningNode,
 // DeleteLightningNode starts a new database transaction to remove a vertex/node
 // from the database according to the node's public key.
 func (c *ChannelGraph) DeleteLightningNode(nodePub route.Vertex) error {
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	err := c.KVStore.DeleteLightningNode(nodePub)
 	if err != nil {
 		return err
@@ -333,9 +322,6 @@ func (c *ChannelGraph) DeleteLightningNode(nodePub route.Vertex) error {
 func (c *ChannelGraph) AddChannelEdge(edge *models.ChannelEdgeInfo,
 	op ...batch.SchedulerOption) error {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	err := c.KVStore.AddChannelEdge(edge, op...)
 	if err != nil {
 		return err
@@ -358,9 +344,6 @@ func (c *ChannelGraph) AddChannelEdge(edge *models.ChannelEdgeInfo,
 // If the cache is enabled, the edge will be added back to the graph cache if
 // we still have a record of this channel in the DB.
 func (c *ChannelGraph) MarkEdgeLive(chanID uint64) error {
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	err := c.KVStore.MarkEdgeLive(chanID)
 	if err != nil {
 		return err
@@ -397,9 +380,6 @@ func (c *ChannelGraph) MarkEdgeLive(chanID uint64) error {
 func (c *ChannelGraph) DeleteChannelEdges(strictZombiePruning, markZombie bool,
 	chanIDs ...uint64) error {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	infos, err := c.KVStore.DeleteChannelEdges(
 		strictZombiePruning, markZombie, chanIDs...,
 	)
@@ -429,9 +409,6 @@ func (c *ChannelGraph) DeleteChannelEdges(strictZombiePruning, markZombie bool,
 func (c *ChannelGraph) DisconnectBlockAtHeight(height uint32) (
 	[]*models.ChannelEdgeInfo, error) {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	edges, err := c.KVStore.DisconnectBlockAtHeight(height)
 	if err != nil {
 		return nil, err
@@ -460,9 +437,6 @@ func (c *ChannelGraph) PruneGraph(spentOutputs []*wire.OutPoint,
 	blockHash *chainhash.Hash, blockHeight uint32) (
 	[]*models.ChannelEdgeInfo, error) {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	edges, nodes, err := c.KVStore.PruneGraph(
 		spentOutputs, blockHash, blockHeight,
 	)
@@ -505,9 +479,6 @@ func (c *ChannelGraph) PruneGraph(spentOutputs []*wire.OutPoint,
 // that we only maintain a graph of reachable nodes. In the event that a pruned
 // node gains more channels, it will be re-added back to the graph.
 func (c *ChannelGraph) PruneGraphNodes() error {
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	nodes, err := c.KVStore.PruneGraphNodes()
 	if err != nil {
 		return err
@@ -580,9 +551,6 @@ func (c *ChannelGraph) FilterKnownChanIDs(chansInfo []ChannelUpdateInfo,
 func (c *ChannelGraph) MarkEdgeZombie(chanID uint64,
 	pubKey1, pubKey2 [33]byte) error {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	err := c.KVStore.MarkEdgeZombie(chanID, pubKey1, pubKey2)
 	if err != nil {
 		return err
@@ -605,9 +573,6 @@ func (c *ChannelGraph) MarkEdgeZombie(chanID uint64,
 func (c *ChannelGraph) UpdateEdgePolicy(edge *models.ChannelEdgePolicy,
 	op ...batch.SchedulerOption) error {
 
-	c.cacheMu.Lock()
-	defer c.cacheMu.Unlock()
-
 	from, to, err := c.KVStore.UpdateEdgePolicy(edge, op...)
 	if err != nil {
 		return err