SERVER-41006 Make replBatchLimitBytes configurable

(cherry picked from commit 887e13622f1e3ffecefbed4f42bae62666680ee4)

3 files changed, 26 insertions, 6 deletions

diff --git a/src/mongo/db/repl/data_replicator_external_state_impl.cpp b/src/mongo/db/repl/data_replicator_external_state_impl.cpp
index bd32ead02a5..599e635a4d6 100644
--- a/src/mongo/db/repl/data_replicator_external_state_impl.cpp
+++ b/src/mongo/db/repl/data_replicator_external_state_impl.cpp
@@ -154,7 +154,7 @@ StatusWith<OplogApplier::Operations> DataReplicatorExternalStateImpl::getNextApp
     OplogApplier oplogApplier(
         nullptr, oplogBuffer, nullptr, nullptr, nullptr, nullptr, {}, nullptr);
     OplogApplier::BatchLimits batchLimits;
-    batchLimits.bytes = SyncTail::replBatchLimitBytes;
+    batchLimits.bytes = std::size_t(SyncTail::replBatchLimitBytes.load());
     batchLimits.ops = std::size_t(SyncTail::replBatchLimitOperations.load());
     return oplogApplier.getNextApplierBatch(opCtx, batchLimits);
 }
diff --git a/src/mongo/db/repl/sync_tail.cpp b/src/mongo/db/repl/sync_tail.cpp
index e507a9338ab..90e7b7d23ce 100644
--- a/src/mongo/db/repl/sync_tail.cpp
+++ b/src/mongo/db/repl/sync_tail.cpp
@@ -91,6 +91,7 @@ using std::endl;
 namespace repl {
 
 AtomicInt32 SyncTail::replBatchLimitOperations{5 * 1000};
+AtomicInt32 SyncTail::replBatchLimitBytes{100 * 1024 * 1024};
 
 namespace {
 
@@ -139,6 +140,25 @@ public:
     }
 } exportedBatchLimitOperationsParam;
 
+class ExportedBatchLimitBytesParameter
+    : public ExportedServerParameter<int, ServerParameterType::kStartupAndRuntime> {
+public:
+    ExportedBatchLimitBytesParameter()
+        : ExportedServerParameter<int, ServerParameterType::kStartupAndRuntime>(
+              ServerParameterSet::getGlobal(),
+              "replBatchLimitBytes",
+              &SyncTail::replBatchLimitBytes) {}
+
+    virtual Status validate(const int& potentialNewValue) {
+        if (potentialNewValue < (16 * 1024 * 1024) || potentialNewValue > (100 * 1024 * 1024)) {
+            return Status(ErrorCodes::BadValue,
+                          "replBatchLimitBytes must be between 16MB and 100MB, inclusive");
+        }
+
+        return Status::OK();
+    }
+} exportedBatchLimitBytesParam;
+
 // The oplog entries applied
 Counter64 opsAppliedStats;
 ServerStatusMetricField<Counter64> displayOpsApplied("repl.apply.ops", &opsAppliedStats);
@@ -324,7 +344,7 @@ std::size_t SyncTail::calculateBatchLimitBytes(OperationContext* opCtx,
     auto oplogMaxSizeResult =
         storageInterface->getOplogMaxSize(opCtx, NamespaceString::kRsOplogNamespace);
     auto oplogMaxSize = fassert(40301, oplogMaxSizeResult);
-    return std::min(oplogMaxSize / 10, std::size_t(replBatchLimitBytes));
+    return std::min(oplogMaxSize / 10, std::size_t(replBatchLimitBytes.load()));
 }
 
 std::unique_ptr<ThreadPool> SyncTail::makeWriterPool() {
@@ -840,14 +860,14 @@ private:
         Client::initThread("ReplBatcher");
 
         BatchLimits batchLimits;
-        batchLimits.bytes =
-            calculateBatchLimitBytes(cc().makeOperationContext().get(), _storageInterface);
 
         while (true) {
             batchLimits.slaveDelayLatestTimestamp = _calculateSlaveDelayLatestTimestamp();
 
-            // Check this once per batch since users can change it at runtime.
+            // Check the limits once per batch since users can change them at runtime.
             batchLimits.ops = replBatchLimitOperations.load();
+            batchLimits.bytes =
+                calculateBatchLimitBytes(cc().makeOperationContext().get(), _storageInterface);
 
             OpQueue ops(batchLimits.ops);
             // tryPopAndWaitForMore adds to ops and returns true when we need to end a batch early.
diff --git a/src/mongo/db/repl/sync_tail.h b/src/mongo/db/repl/sync_tail.h
index af12ea68ef3..914252690df 100644
--- a/src/mongo/db/repl/sync_tail.h
+++ b/src/mongo/db/repl/sync_tail.h
@@ -80,7 +80,7 @@ public:
     /**
      * Lower bound of batch limit size (in bytes) returned by calculateBatchLimitBytes().
      */
-    static const unsigned int replBatchLimitBytes = 100 * 1024 * 1024;
+    static AtomicInt32 replBatchLimitBytes;
 
     /**
      * Calculates batch limit size (in bytes) using the maximum capped collection size of the oplog