Mandate flow control in bytes (#4353)

Resolves #3781 and #4374.

This change removes the `ENABLE_FLOW_CONTROL_BYTES` config option and
always uses flow control in bytes.

# Checklist
- [x] Reviewed the
[contributing](https://github.com/stellar/stellar-core/blob/master/CONTRIBUTING.md#submitting-changes)
document
- [x] Rebased on top of master (no merge commits)
- [x] Ran `clang-format` v8.0.0 (via `make format` or the Visual Studio
extension)
- [x] Compiles
- [x] Ran all tests
- [ ] If change impacts performance, include supporting evidence per the
[performance
document](https://github.com/stellar/stellar-core/blob/master/performance-eval/performance-eval.md)

docs/stellar-core_example.cfg

@@ -530,11 +530,6 @@ PEER_FLOOD_READING_CAPACITY_BYTES=300000
 # processes `FLOW_CONTROL_SEND_MORE_BATCH_SIZE_BYTES` bytes
 FLOW_CONTROL_SEND_MORE_BATCH_SIZE_BYTES=100000
 
-# Enable flow control in bytes. This config allows core to process large
-# transactions on the network more efficiently and apply back pressure if
-# needed.
-ENABLE_FLOW_CONTROL_BYTES=true
-
 # Byte limit for outbound transaction queue.
 OUTBOUND_TX_QUEUE_BYTE_LIMIT=3145728
 

src/herder/Herder.h

@@ -153,6 +153,7 @@ class Herder
 
     virtual VirtualTimer const& getTriggerTimer() const = 0;
     virtual void setMaxClassicTxSize(uint32 bytes) = 0;
+    virtual void setMaxTxSize(uint32 bytes) = 0;
     virtual void setFlowControlExtraBufferSize(uint32 bytes) = 0;
 
     virtual ClassicTransactionQueue& getTransactionQueue() = 0;

src/herder/HerderImpl.h

@@ -126,6 +126,11 @@ class HerderImpl : public Herder
     {
         mMaxClassicTxSize = std::make_optional<uint32_t>(bytes);
     }
+    void
+    setMaxTxSize(uint32 bytes) override
+    {
+        mMaxTxSize = bytes;
+    }
     std::optional<uint32_t> mFlowControlExtraBuffer;
     void
     setFlowControlExtraBufferSize(uint32 bytes) override

src/main/Config.cpp

@@ -151,8 +151,8 @@ Config::Config() : NODE_SEED(SecretKey::random())
     LEDGER_PROTOCOL_VERSION = CURRENT_LEDGER_PROTOCOL_VERSION;
     LEDGER_PROTOCOL_MIN_VERSION_INTERNAL_ERROR_REPORT = 18;
 
-    OVERLAY_PROTOCOL_MIN_VERSION = 32;
-    OVERLAY_PROTOCOL_VERSION = 34;
+    OVERLAY_PROTOCOL_MIN_VERSION = 33;
+    OVERLAY_PROTOCOL_VERSION = 35;
 
     VERSION_STR = STELLAR_CORE_VERSION;
 
@@ -261,7 +261,6 @@ Config::Config() : NODE_SEED(SecretKey::random())
     PEER_FLOOD_READING_CAPACITY_BYTES = 0;
     FLOW_CONTROL_SEND_MORE_BATCH_SIZE_BYTES = 0;
     OUTBOUND_TX_QUEUE_BYTE_LIMIT = 1024 * 1024 * 3;
-    ENABLE_FLOW_CONTROL_BYTES = true;
 
     // WORKER_THREADS: setting this too low risks a form of priority inversion
     // where a long-running background task occupies all worker threads and
@@ -1031,10 +1030,6 @@ Config::processConfig(std::shared_ptr<cpptoml::table> t)
                 FLOW_CONTROL_SEND_MORE_BATCH_SIZE_BYTES =
                     readInt<uint32_t>(item, 1);
             }
-            else if (item.first == "ENABLE_FLOW_CONTROL_BYTES")
-            {
-                ENABLE_FLOW_CONTROL_BYTES = readBool(item);
-            }
             else if (item.first == "OUTBOUND_TX_QUEUE_BYTE_LIMIT")
             {
                 OUTBOUND_TX_QUEUE_BYTE_LIMIT = readInt<uint32_t>(item, 1);

src/main/Config.h

@@ -324,11 +324,6 @@ class Config : public std::enable_shared_from_this<Config>
     uint32_t PEER_FLOOD_READING_CAPACITY_BYTES;
     uint32_t FLOW_CONTROL_SEND_MORE_BATCH_SIZE_BYTES;
 
-    // Enable flow control in bytes. This config allows core to process large
-    // transactions on the network more efficiently and apply back pressure if
-    // needed.
-    bool ENABLE_FLOW_CONTROL_BYTES;
-
     // Byte limit for outbound transaction queue.
     uint32_t OUTBOUND_TX_QUEUE_BYTE_LIMIT;