Grow the open ledger expected transactions quickly (RIPD-1630):

* When increasing the expected ledger size, add on an extra 20%.
* When decreasing the expected ledger size, take the minimum of the
  validated ledger size or the old expected size, and subract another 50%.
* Update fee escalation documentation.
* Refactor the FeeMetrics object to use values from Setup

src/test/app/TxQ_test.cpp

@@ -108,6 +108,7 @@ class TxQ_test : public beast::unit_test::suite
         section.set("max_ledger_counts_to_store", "100");
         section.set("retry_sequence_percent", "25");
         section.set("zero_basefee_transaction_feelevel", "100000000000");
+        section.set("normal_consensus_increase_percent", "0");
 
         for (auto const& value : extraTxQ)
             section.set(value.first, value.second);
@@ -2811,6 +2812,141 @@ public:
         }
     }
 
+    void
+    testScaling()
+    {
+        using namespace jtx;
+        using namespace std::chrono_literals;
+
+        {
+            Env env(*this,
+                makeConfig({ { "minimum_txn_in_ledger_standalone", "3" },
+                    { "normal_consensus_increase_percent", "25" },
+                    { "slow_consensus_decrease_percent", "50" },
+                    { "target_txn_in_ledger", "10" },
+                    { "maximum_txn_per_account", "200" } }));
+            auto alice = Account("alice");
+
+            checkMetrics(env, 0, boost::none, 0, 3, 256);
+            env.fund(XRP(50000000), alice);
+
+            fillQueue(env, alice);
+            checkMetrics(env, 0, boost::none, 4, 3, 256);
+            auto seqAlice = env.seq(alice);
+            auto txCount = 140;
+            for (int i = 0; i < txCount; ++i)
+                env(noop(alice), seq(seqAlice++), ter(terQUEUED));
+            checkMetrics(env, txCount, boost::none, 4, 3, 256);
+
+            // Close a few ledgers successfully, so the limit grows
+
+            env.close();
+            // 4 + 25% = 5
+            txCount -= 6;
+            checkMetrics(env, txCount, 10, 6, 5, 257);
+
+            env.close();
+            // 6 + 25% = 7
+            txCount -= 8;
+            checkMetrics(env, txCount, 14, 8, 7, 257);
+
+            env.close();
+            // 8 + 25% = 10
+            txCount -= 11;
+            checkMetrics(env, txCount, 20, 11, 10, 257);
+
+            env.close();
+            // 11 + 25% = 13
+            txCount -= 14;
+            checkMetrics(env, txCount, 26, 14, 13, 257);
+
+            env.close();
+            // 14 + 25% = 17
+            txCount -= 18;
+            checkMetrics(env, txCount, 34, 18, 17, 257);
+
+            env.close();
+            // 18 + 25% = 22
+            txCount -= 23;
+            checkMetrics(env, txCount, 44, 23, 22, 257);
+
+            env.close();
+            // 23 + 25% = 28
+            txCount -= 29;
+            checkMetrics(env, txCount, 56, 29, 28, 256);
+
+            // From 3 expected to 28 in 7 "fast" ledgers.
+
+            // Close the ledger with a delay.
+            env.close(env.now() + 5s, 10000ms);
+            txCount -= 15;
+            checkMetrics(env, txCount, 56, 15, 14, 256);
+
+            // Close the ledger with a delay.
+            env.close(env.now() + 5s, 10000ms);
+            txCount -= 8;
+            checkMetrics(env, txCount, 56, 8, 7, 256);
+
+            // Close the ledger with a delay.
+            env.close(env.now() + 5s, 10000ms);
+            txCount -= 4;
+            checkMetrics(env, txCount, 56, 4, 3, 256);
+
+            // From 28 expected back down to 3 in 3 "slow" ledgers.
+
+            // Confirm the minimum sticks
+            env.close(env.now() + 5s, 10000ms);
+            txCount -= 4;
+            checkMetrics(env, txCount, 56, 4, 3, 256);
+
+            BEAST_EXPECT(!txCount);
+        }
+
+        {
+            Env env(*this,
+                makeConfig({ { "minimum_txn_in_ledger_standalone", "3" },
+                    { "normal_consensus_increase_percent", "150" },
+                    { "slow_consensus_decrease_percent", "150" },
+                    { "target_txn_in_ledger", "10" },
+                    { "maximum_txn_per_account", "200" } }));
+            auto alice = Account("alice");
+
+            checkMetrics(env, 0, boost::none, 0, 3, 256);
+            env.fund(XRP(50000000), alice);
+
+            fillQueue(env, alice);
+            checkMetrics(env, 0, boost::none, 4, 3, 256);
+            auto seqAlice = env.seq(alice);
+            auto txCount = 43;
+            for (int i = 0; i < txCount; ++i)
+                env(noop(alice), seq(seqAlice++), ter(terQUEUED));
+            checkMetrics(env, txCount, boost::none, 4, 3, 256);
+
+            // Close a few ledgers successfully, so the limit grows
+
+            env.close();
+            // 4 + 150% = 10
+            txCount -= 11;
+            checkMetrics(env, txCount, 20, 11, 10, 257);
+
+            env.close();
+            // 11 + 150% = 27
+            txCount -= 28;
+            checkMetrics(env, txCount, 54, 28, 27, 256);
+
+            // From 3 expected to 28 in 7 "fast" ledgers.
+
+            // Close the ledger with a delay.
+            env.close(env.now() + 5s, 10000ms);
+            txCount -= 4;
+            checkMetrics(env, txCount, 54, 4, 3, 256);
+
+            // From 28 expected back down to 3 in 3 "slow" ledgers.
+
+            BEAST_EXPECT(!txCount);
+        }
+    }
+    
     void run() override
     {
         testQueue();
@@ -2835,6 +2971,7 @@ public:
         testServerInfo();
         testServerSubscribe();
         testClearQueuedAccountTxs();
+        testScaling();
     }
 };