graph/db+sqldb: find best default query cfg values for sqlite & postgres

This commit adds a BenchmarkFindOptimalSQLQueryConfig test in the
graph/db package which runs ForEachNode and ForEachChannel queries
against a local backend using various different values for the sql
QueryConfig struct. This is done to determine good default values to
use for the config options for sqlite vs postgres.

sqldb/paginate.go

@@ -15,6 +15,20 @@ const (
 	// included in a batch query IN clause for Postgres. This was determined
 	// using the TestSQLSliceQueries test.
 	maxPostgresBatchSize = 65535
+
+	// defaultSQLitePageSize is the default page size for SQLite queries.
+	defaultSQLitePageSize = 100
+
+	// defaultPostgresPageSize is the default page size for Postgres
+	// queries.
+	defaultPostgresPageSize = 10500
+
+	// defaultSQLiteBatchSize is the default batch size for SQLite queries.
+	defaultSQLiteBatchSize = 250
+
+	// defaultPostgresBatchSize is the default batch size for Postgres
+	// queries.
+	defaultPostgresBatchSize = 5000
 )
 
 // QueryConfig holds configuration values for SQL queries.
@@ -66,6 +80,24 @@ func DefaultQueryConfig() *QueryConfig {
 	}
 }
 
+// DefaultSQLiteConfig returns a default configuration for SQL queries to a
+// SQLite backend.
+func DefaultSQLiteConfig() *QueryConfig {
+	return &QueryConfig{
+		MaxBatchSize: defaultSQLiteBatchSize,
+		MaxPageSize:  defaultSQLitePageSize,
+	}
+}
+
+// DefaultPostgresConfig returns a default configuration for SQL queries to a
+// Postgres backend.
+func DefaultPostgresConfig() *QueryConfig {
+	return &QueryConfig{
+		MaxBatchSize: defaultPostgresBatchSize,
+		MaxPageSize:  defaultPostgresPageSize,
+	}
+}
+
 // BatchQueryFunc represents a function that takes a batch of converted items
 // and returns results.
 type BatchQueryFunc[T any, R any] func(context.Context, []T) ([]R, error)