Track first recorded height

Track the first time we seen txs in a block that we have been tracking in our mempool. Used to evaluate validity of fee estimates for different targets.

src/policy/fees.cpp

@@ -477,7 +477,7 @@ bool CBlockPolicyEstimator::removeTx(uint256 hash, bool inBlock)
 }
 
 CBlockPolicyEstimator::CBlockPolicyEstimator()
-    : nBestSeenHeight(0), trackedTxs(0), untrackedTxs(0)
+    : nBestSeenHeight(0), firstRecordedHeight(0), trackedTxs(0), untrackedTxs(0)
 {
     static_assert(MIN_BUCKET_FEERATE > 0, "Min feerate must be nonzero");
     minTrackedFee = CFeeRate(MIN_BUCKET_FEERATE);
@@ -603,6 +603,11 @@ void CBlockPolicyEstimator::processBlock(unsigned int nBlockHeight,
             countedTxs++;
     }
 
+    if (firstRecordedHeight == 0 && countedTxs > 0) {
+        firstRecordedHeight = nBestSeenHeight;
+        LogPrint(BCLog::ESTIMATEFEE, "Blockpolicy first recorded height %u\n", firstRecordedHeight);
+    }
+
 
     LogPrint(BCLog::ESTIMATEFEE, "Blockpolicy after updating estimates for %u of %u txs in block, since last block %u of %u tracked, new mempool map size %u\n",
              countedTxs, entries.size(), trackedTxs, trackedTxs + untrackedTxs, mapMemPoolTxs.size());

src/policy/fees.h

@@ -173,6 +173,10 @@ public:
 private:
     CFeeRate minTrackedFee;    //!< Passed to constructor to avoid dependency on main
     unsigned int nBestSeenHeight;
+    unsigned int firstRecordedHeight;
+    unsigned int historicalFirst;
+    unsigned int historicalBest;
+
     struct TxStatsInfo
     {
         unsigned int blockHeight;