diff --git a/db/flush_job.cc b/db/flush_job.cc
index 2190c45c2..23ca044c0 100644
--- a/db/flush_job.cc
+++ b/db/flush_job.cc
@@ -249,7 +249,8 @@ Status FlushJob::Run(LogsWithPrepTracker* prep_tracker,
   }
   RecordFlushIOStats();
 
-  auto stream = event_logger_->LogToBuffer(log_buffer_);
+  // When measure_io_stats_ is true, the default 512 bytes is not enough.
+  auto stream = event_logger_->LogToBuffer(log_buffer_, 1024);
   stream << "job" << job_context_->job_id << "event"
          << "flush_finished";
   stream << "output_compression"
diff --git a/logging/event_logger.cc b/logging/event_logger.cc
index 4ae9d2d66..5e07fd96f 100644
--- a/logging/event_logger.cc
+++ b/logging/event_logger.cc
@@ -15,12 +15,18 @@
 
 namespace rocksdb {
 
-
 EventLoggerStream::EventLoggerStream(Logger* logger)
-    : logger_(logger), log_buffer_(nullptr), json_writer_(nullptr) {}
+    : logger_(logger),
+      log_buffer_(nullptr),
+      max_log_size_(0),
+      json_writer_(nullptr) {}
 
-EventLoggerStream::EventLoggerStream(LogBuffer* log_buffer)
-    : logger_(nullptr), log_buffer_(log_buffer), json_writer_(nullptr) {}
+EventLoggerStream::EventLoggerStream(LogBuffer* log_buffer,
+                                     const size_t max_log_size)
+    : logger_(nullptr),
+      log_buffer_(log_buffer),
+      max_log_size_(max_log_size),
+      json_writer_(nullptr) {}
 
 EventLoggerStream::~EventLoggerStream() {
   if (json_writer_) {
@@ -31,7 +37,8 @@ EventLoggerStream::~EventLoggerStream() {
     if (logger_) {
       EventLogger::Log(logger_, *json_writer_);
     } else if (log_buffer_) {
-      EventLogger::LogToBuffer(log_buffer_, *json_writer_);
+      assert(max_log_size_);
+      EventLogger::LogToBuffer(log_buffer_, *json_writer_, max_log_size_);
     }
 #endif
     delete json_writer_;
@@ -50,13 +57,14 @@ void EventLogger::Log(Logger* logger, const JSONWriter& jwriter) {
 #endif
 }
 
-void EventLogger::LogToBuffer(
-    LogBuffer* log_buffer, const JSONWriter& jwriter) {
+void EventLogger::LogToBuffer(LogBuffer* log_buffer, const JSONWriter& jwriter,
+                              const size_t max_log_size) {
 #ifdef ROCKSDB_PRINT_EVENTS_TO_STDOUT
   printf("%s\n", jwriter.Get().c_str());
 #else
   assert(log_buffer);
-  rocksdb::LogToBuffer(log_buffer, "%s %s", Prefix(), jwriter.Get().c_str());
+  rocksdb::LogToBuffer(log_buffer, max_log_size, "%s %s", Prefix(),
+                       jwriter.Get().c_str());
 #endif
 }
 
diff --git a/logging/event_logger.h b/logging/event_logger.h
index c3a7c30c6..6206993c8 100644
--- a/logging/event_logger.h
+++ b/logging/event_logger.h
@@ -162,10 +162,11 @@ class EventLoggerStream {
   }
   friend class EventLogger;
   explicit EventLoggerStream(Logger* logger);
-  explicit EventLoggerStream(LogBuffer* log_buffer);
+  explicit EventLoggerStream(LogBuffer* log_buffer, const size_t max_log_size);
   // exactly one is non-nullptr
   Logger* const logger_;
   LogBuffer* const log_buffer_;
+  const size_t max_log_size_;  // used only for log_buffer_
   // ownership
   JSONWriter* json_writer_;
 };
@@ -183,11 +184,17 @@ class EventLogger {
   explicit EventLogger(Logger* logger) : logger_(logger) {}
   EventLoggerStream Log() { return EventLoggerStream(logger_); }
   EventLoggerStream LogToBuffer(LogBuffer* log_buffer) {
-    return EventLoggerStream(log_buffer);
+    return EventLoggerStream(log_buffer, LogBuffer::kDefaultMaxLogSize);
+  }
+  EventLoggerStream LogToBuffer(LogBuffer* log_buffer,
+                                const size_t max_log_size) {
+    return EventLoggerStream(log_buffer, max_log_size);
   }
   void Log(const JSONWriter& jwriter);
   static void Log(Logger* logger, const JSONWriter& jwriter);
-  static void LogToBuffer(LogBuffer* log_buffer, const JSONWriter& jwriter);
+  static void LogToBuffer(
+      LogBuffer* log_buffer, const JSONWriter& jwriter,
+      const size_t max_log_size = LogBuffer::kDefaultMaxLogSize);
 
  private:
   Logger* logger_;
diff --git a/logging/log_buffer.cc b/logging/log_buffer.cc
index 74db11c66..5327c1814 100644
--- a/logging/log_buffer.cc
+++ b/logging/log_buffer.cc
@@ -81,11 +81,10 @@ void LogToBuffer(LogBuffer* log_buffer, size_t max_log_size, const char* format,
 }
 
 void LogToBuffer(LogBuffer* log_buffer, const char* format, ...) {
-  const size_t kDefaultMaxLogSize = 512;
   if (log_buffer != nullptr) {
     va_list ap;
     va_start(ap, format);
-    log_buffer->AddLogToBuffer(kDefaultMaxLogSize, format, ap);
+    log_buffer->AddLogToBuffer(LogBuffer::kDefaultMaxLogSize, format, ap);
     va_end(ap);
   }
 }
diff --git a/logging/log_buffer.h b/logging/log_buffer.h
index 16fb24311..b54bf4d49 100644
--- a/logging/log_buffer.h
+++ b/logging/log_buffer.h
@@ -30,6 +30,7 @@ class LogBuffer {
 
   // Flush all buffered log to the info log.
   void FlushBufferToLog();
+  static const size_t kDefaultMaxLogSize = 512;
 
  private:
   // One log entry with its timestamp