update estimatesmartfee

estimatesmartfee will now return the maximum of feeRate returned by
estimateSmartFee, mempoolMinFee and  minRelayTxFee.
The test has been changed such that when a the node is restarted with a
high mempoolMinFee, the estimatesmartfee still returns a feeRate greater
than or equal to the mempoolMinFee, minRelayTxFee.(which is closer to
what a user would have to pay in an actual transaction)

src/rpc/mining.cpp

@@ -1097,6 +1097,8 @@ static RPCHelpMan estimatesmartfee()
     RPCTypeCheckArgument(request.params[0], UniValue::VNUM);
 
     CBlockPolicyEstimator& fee_estimator = EnsureAnyFeeEstimator(request.context);
+    const NodeContext& node = EnsureAnyNodeContext(request.context);
+    const CTxMemPool& mempool = EnsureMemPool(node);
 
     unsigned int max_target = fee_estimator.HighestTargetTracked(FeeEstimateHorizon::LONG_HALFLIFE);
     unsigned int conf_target = ParseConfirmTarget(request.params[0], max_target);
@@ -1112,7 +1114,10 @@ static RPCHelpMan estimatesmartfee()
     UniValue result(UniValue::VOBJ);
     UniValue errors(UniValue::VARR);
     FeeCalculation feeCalc;
-    CFeeRate feeRate = fee_estimator.estimateSmartFee(conf_target, &feeCalc, conservative);
+    CFeeRate feeRate{fee_estimator.estimateSmartFee(conf_target, &feeCalc, conservative)};
+    CFeeRate min_mempool_feerate{mempool.GetMinFee(gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000)};
+    CFeeRate min_relay_feerate{::minRelayTxFee};
+    feeRate = std::max({feeRate, min_mempool_feerate, min_relay_feerate});
     if (feeRate != CFeeRate(0)) {
         result.pushKV("feerate", ValueFromAmount(feeRate.GetFeePerK()));
     } else {

test/functional/feature_fee_estimation.py

@@ -132,9 +132,13 @@ def check_smart_estimates(node, fees_seen):
     delta = 1.0e-6  # account for rounding error
     last_feerate = float(max(fees_seen))
     all_smart_estimates = [node.estimatesmartfee(i) for i in range(1, 26)]
+    mempoolMinFee = node.getmempoolinfo()['mempoolminfee']
+    minRelaytxFee = node.getmempoolinfo()['minrelaytxfee']
     for i, e in enumerate(all_smart_estimates):  # estimate is for i+1
         feerate = float(e["feerate"])
         assert_greater_than(feerate, 0)
+        assert_greater_than_or_equal(feerate, float(mempoolMinFee))
+        assert_greater_than_or_equal(feerate, float(minRelaytxFee))
 
         if feerate + delta < min(fees_seen) or feerate - delta > max(fees_seen):
             raise AssertionError(f"Estimated fee ({feerate}) out of range ({min(fees_seen)},{max(fees_seen)})")
@@ -275,6 +279,11 @@ def run_test(self):
         self.log.info("Final estimates after emptying mempools")
         check_estimates(self.nodes[1], self.fees_per_kb)
 
+        # check that the effective feerate is greater than or equal to the mempoolminfee even for high mempoolminfee
+        self.log.info("Test fee rate estimation after restarting node with high MempoolMinFee")
+        self.restart_node(1, extra_args=['-minrelaytxfee=0.0003'])
+        check_estimates(self.nodes[1], self.fees_per_kb)
+
         self.log.info("Testing that fee estimation is disabled in blocksonly.")
         self.restart_node(0, ["-blocksonly"])
         assert_raises_rpc_error(-32603, "Fee estimation disabled",