Rewrite estimateSmartFee

Change the logic of estimateSmartFee to check a 60% threshold at half the target, a 85% threshold at the target and a 95% threshold at double the target. Always check the shortest time horizon possible and ensure that estimates are monotonically decreasing.  Add a conservative mode, which makes sure that the 95% threshold is also met at longer time horizons as well.

2 files changed, 15 insertions, 5 deletions

diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index afc1fa1c79..455d1dc722 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -106,6 +106,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "getrawmempool", 0, "verbose" },
     { "estimatefee", 0, "nblocks" },
     { "estimatesmartfee", 0, "nblocks" },
+    { "estimatesmartfee", 1, "conservative" },
     { "estimaterawfee", 0, "nblocks" },
     { "estimaterawfee", 1, "threshold" },
     { "estimaterawfee", 2, "horizon" },
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 74e5ba5f44..9f6cab861c 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -828,16 +828,20 @@ UniValue estimatefee(const JSONRPCRequest& request)
 
 UniValue estimatesmartfee(const JSONRPCRequest& request)
 {
-    if (request.fHelp || request.params.size() != 1)
+    if (request.fHelp || request.params.size() < 1 || request.params.size() > 2)
         throw std::runtime_error(
-            "estimatesmartfee nblocks\n"
+            "estimatesmartfee nblocks (conservative)\n"
             "\nWARNING: This interface is unstable and may disappear or change!\n"
             "\nEstimates the approximate fee per kilobyte needed for a transaction to begin\n"
             "confirmation within nblocks blocks if possible and return the number of blocks\n"
             "for which the estimate is valid. Uses virtual transaction size as defined\n"
             "in BIP 141 (witness data is discounted).\n"
             "\nArguments:\n"
-            "1. nblocks     (numeric)\n"
+            "1. nblocks       (numeric)\n"
+            "2. conservative  (bool, optional, default=true) Whether to return a more conservative estimate which\n"
+            "                 also satisfies a longer history. A conservative estimate potentially returns a higher\n"
+            "                 feerate and is more likely to be sufficient for the desired target, but is not as\n"
+            "                 responsive to short term drops in the prevailing fee market\n"
             "\nResult:\n"
             "{\n"
             "  \"feerate\" : x.x,     (numeric) estimate fee-per-kilobyte (in BTC)\n"
@@ -854,10 +858,15 @@ UniValue estimatesmartfee(const JSONRPCRequest& request)
     RPCTypeCheck(request.params, boost::assign::list_of(UniValue::VNUM));
 
     int nBlocks = request.params[0].get_int();
+    bool conservative = true;
+    if (request.params.size() > 1 && !request.params[1].isNull()) {
+        RPCTypeCheckArgument(request.params[1], UniValue::VBOOL);
+        conservative = request.params[1].get_bool();
+    }
 
     UniValue result(UniValue::VOBJ);
     int answerFound;
-    CFeeRate feeRate = ::feeEstimator.estimateSmartFee(nBlocks, &answerFound, ::mempool);
+    CFeeRate feeRate = ::feeEstimator.estimateSmartFee(nBlocks, &answerFound, ::mempool, conservative);
     result.push_back(Pair("feerate", feeRate == CFeeRate(0) ? -1.0 : ValueFromAmount(feeRate.GetFeePerK())));
     result.push_back(Pair("blocks", answerFound));
     return result;
@@ -951,7 +960,7 @@ static const CRPCCommand commands[] =
     { "generating",         "generatetoaddress",      &generatetoaddress,      true,  {"nblocks","address","maxtries"} },
 
     { "util",               "estimatefee",            &estimatefee,            true,  {"nblocks"} },
-    { "util",               "estimatesmartfee",       &estimatesmartfee,       true,  {"nblocks"} },
+    { "util",               "estimatesmartfee",       &estimatesmartfee,       true,  {"nblocks", "conservative"} },
 
     { "hidden",             "estimaterawfee",         &estimaterawfee,         true,  {"nblocks", "threshold", "horizon"} },
 };