Improve eth_flush performance by disabling wait in Client::doWork

CHANGELOG.md

@@ -14,6 +14,7 @@
 - Fixed: [#5452](https://github.com/ethereum/aleth/pull/5452) Correctly handle Discovery messages when the peer changes public key.
 - Fixed: [#5519](https://github.com/ethereum/aleth/pull/5519) Correctly handle Discovery messages with known public key but unknown endpoint.
 - Fixed: [#5523](https://github.com/ethereum/aleth/pull/5523) [#5533](https://github.com/ethereum/aleth/pull/5533) Fix syncing terminating prematurely because of race condition.
-- Fixed: [#5539](https://github.com/ethereum/aleth/pull/5539) Fix logic for determining if dao hard fork block header should be requested
+- Fixed: [#5539](https://github.com/ethereum/aleth/pull/5539) Fix logic for determining if dao hard fork block header should be requested.
+- Fixed: [#5547](https://github.com/ethereum/aleth/pull/5547) Fix unnecessary slow-down of eth_flush RPC method.
 
 [1.6.0]: https://github.com/ethereum/aleth/compare/v1.6.0-alpha.1...master

libethereum/Client.cpp

@@ -791,7 +791,7 @@ Block Client::block(h256 const& _blockHash, PopulationStatistics* o_stats) const
 
 void Client::flushTransactions()
 {
-    doWork();
+    doWork(false);
 }
 
 Transactions Client::pending() const