refactor: move graph related DB code to graph/db from channeldb

This is a pure refactor commit. It moves over all the graph related CRUD
code from `channeldb` to `graph/db`.

graph/db/options.go

@@ -0,0 +1,93 @@
+package graphdb
+
+import "time"
+
+const (
+	// DefaultRejectCacheSize is the default number of rejectCacheEntries to
+	// cache for use in the rejection cache of incoming gossip traffic. This
+	// produces a cache size of around 1MB.
+	DefaultRejectCacheSize = 50000
+
+	// DefaultChannelCacheSize is the default number of ChannelEdges cached
+	// in order to reply to gossip queries. This produces a cache size of
+	// around 40MB.
+	DefaultChannelCacheSize = 20000
+
+	// DefaultPreAllocCacheNumNodes is the default number of channels we
+	// assume for mainnet for pre-allocating the graph cache. As of
+	// September 2021, there currently are 14k nodes in a strictly pruned
+	// graph, so we choose a number that is slightly higher.
+	DefaultPreAllocCacheNumNodes = 15000
+)
+
+// Options holds parameters for tuning and customizing a graph.DB.
+type Options struct {
+	// RejectCacheSize is the maximum number of rejectCacheEntries to hold
+	// in the rejection cache.
+	RejectCacheSize int
+
+	// ChannelCacheSize is the maximum number of ChannelEdges to hold in the
+	// channel cache.
+	ChannelCacheSize int
+
+	// BatchCommitInterval is the maximum duration the batch schedulers will
+	// wait before attempting to commit a pending set of updates.
+	BatchCommitInterval time.Duration
+
+	// PreAllocCacheNumNodes is the number of nodes we expect to be in the
+	// graph cache, so we can pre-allocate the map accordingly.
+	PreAllocCacheNumNodes int
+
+	// UseGraphCache denotes whether the in-memory graph cache should be
+	// used or a fallback version that uses the underlying database for
+	// path finding.
+	UseGraphCache bool
+
+	// NoMigration specifies that underlying backend was opened in read-only
+	// mode and migrations shouldn't be performed. This can be useful for
+	// applications that use the channeldb package as a library.
+	NoMigration bool
+}
+
+// DefaultOptions returns an Options populated with default values.
+func DefaultOptions() *Options {
+	return &Options{
+		RejectCacheSize:       DefaultRejectCacheSize,
+		ChannelCacheSize:      DefaultChannelCacheSize,
+		PreAllocCacheNumNodes: DefaultPreAllocCacheNumNodes,
+		UseGraphCache:         true,
+		NoMigration:           false,
+	}
+}
+
+// OptionModifier is a function signature for modifying the default Options.
+type OptionModifier func(*Options)
+
+// WithChannelCacheSize sets the ChannelCacheSize to n.
+func WithChannelCacheSize(n int) OptionModifier {
+	return func(o *Options) {
+		o.ChannelCacheSize = n
+	}
+}
+
+// WithPreAllocCacheNumNodes sets the PreAllocCacheNumNodes to n.
+func WithPreAllocCacheNumNodes(n int) OptionModifier {
+	return func(o *Options) {
+		o.PreAllocCacheNumNodes = n
+	}
+}
+
+// WithBatchCommitInterval sets the batch commit interval for the interval batch
+// schedulers.
+func WithBatchCommitInterval(interval time.Duration) OptionModifier {
+	return func(o *Options) {
+		o.BatchCommitInterval = interval
+	}
+}
+
+// WithUseGraphCache sets the UseGraphCache option to the given value.
+func WithUseGraphCache(use bool) OptionModifier {
+	return func(o *Options) {
+		o.UseGraphCache = use
+	}
+}