Tweak DB and mining defaults (#2598)

* Increase WAL size

* Decreased default work queue size

ethcore/src/miner/miner.rs

@@ -100,7 +100,7 @@ impl Default for MinerOptions {
 			tx_queue_strategy: PrioritizationStrategy::GasFactorAndGasPrice,
 			pending_set: PendingSet::AlwaysQueue,
 			reseal_min_period: Duration::from_secs(2),
-			work_queue_size: 20,
+			work_queue_size: 5,
 			enable_resubmission: true,
 			tx_queue_gas_limit: GasLimit::Auto,
 		}

parity/cli.rs

@@ -164,7 +164,7 @@ Sealing/Mining Options:
   --work-queue-size ITEMS  Specify the number of historical work packages
                            which are kept cached lest a solution is found for
                            them later. High values take more memory but result
-                           in fewer unusable solutions [default: 20].
+                           in fewer unusable solutions [default: 5].
   --tx-gas-limit GAS       Apply a limit of GAS as the maximum amount of gas
                            a single transaction may have for it to be mined.
   --relay-set SET          Set of transactions to relay. SET may be:

util/src/kvdb.rs

@@ -213,7 +213,7 @@ impl Database {
 		if let Some(rate_limit) = config.compaction.write_rate_limit {
 			try!(opts.set_parsed_options(&format!("rate_limiter_bytes_per_sec={}", rate_limit)));
 		}
-		try!(opts.set_parsed_options(&format!("max_total_wal_size={}", 64 * 1024 * 1024)));
+		try!(opts.set_parsed_options(&format!("max_total_wal_size={}", 256 * 1024 * 1024)));
 		opts.set_max_open_files(config.max_open_files);
 		opts.create_if_missing(true);
 		opts.set_use_fsync(false);