diff --git a/src/java/org/apache/cassandra/db/ColumnFamilyStore.java b/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
index 5e9e2ac520af..220d1ee081ef 100644
--- a/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
+++ b/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
@@ -206,6 +206,11 @@ public class ColumnFamilyStore implements ColumnFamilyStoreMBean, Memtable.Owner
                                                           ? executorFactory().withJmxInternal().sequential("MemtablePostFlush")
                                                           : null;
 
+    // Dedicated post-flush executor for local system keyspaces to ensure system/gossip tasks are never blocked by slow user table flushes (CASSANDRA-19597)
+    private static final ExecutorPlus systemPostFlushExecutor = DatabaseDescriptor.isDaemonInitialized()
+                                                                ? executorFactory().withJmxInternal().sequential("SystemMemtablePostFlush")
+                                                                : null;
+
     private static final ExecutorPlus reclaimExecutor = DatabaseDescriptor.isDaemonInitialized()
                                                         ? executorFactory().withJmxInternal().sequential("MemtableReclaimMemory")
                                                         : null;
@@ -364,14 +369,25 @@ TablePaxosRepairHistory get()
 
     public static void shutdownPostFlushExecutor() throws InterruptedException
     {
-        postFlushExecutor.shutdown();
-        postFlushExecutor.awaitTermination(60, TimeUnit.SECONDS);
+        try
+        {
+            if (systemPostFlushExecutor != null)
+                ExecutorUtils.shutdownAndWait(60, TimeUnit.SECONDS, postFlushExecutor, systemPostFlushExecutor);
+            else
+                ExecutorUtils.shutdownAndWait(60, TimeUnit.SECONDS, postFlushExecutor);
+        }
+        catch (TimeoutException e)
+        {
+            logger.warn("Timeout shutting down post-flush executor(s): {}", e.getMessage());
+        }
     }
 
     public static void shutdownExecutorsAndWait(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
     {
         List<ExecutorService> executors = new ArrayList<>();
         Collections.addAll(executors, reclaimExecutor, postFlushExecutor, flushExecutor);
+        if (systemPostFlushExecutor != null)
+            executors.add(systemPostFlushExecutor);
         perDiskflushExecutors.appendAllExecutors(executors);
         ExecutorUtils.shutdownAndWait(timeout, unit, executors);
     }
@@ -1080,7 +1096,7 @@ public Future<CommitLogPosition> switchMemtable(FlushReason reason)
             logFlush(reason);
             Flush flush = new Flush(false);
             flushExecutor.execute(flush);
-            postFlushExecutor.execute(flush.postFlushTask);
+            postFlushExecutor().execute(flush.postFlushTask);
             return flush.postFlushTask;
         }
     }
@@ -1151,12 +1167,12 @@ private Future<CommitLogPosition> waitForFlushes()
         // we grab the current memtable; once any preceding memtables have flushed, we know its
         // commitLogLowerBound has been set (as this it is set with the upper bound of the preceding memtable)
         final Memtable current = data.getView().getCurrentMemtable();
-        return postFlushExecutor.submit(current::getCommitLogLowerBound);
+        return postFlushExecutor().submit(current::getCommitLogLowerBound);
     }
 
     public Future<Void> waitForPriorFlushes()
     {
-        return postFlushExecutor.submit(() -> null);
+        return postFlushExecutor().submit(() -> null);
     }
 
     public CommitLogPosition forceBlockingFlush(FlushReason reason)
@@ -2704,11 +2720,18 @@ public Future<CommitLogPosition> dumpMemtable()
         {
             final Flush flush = new Flush(true);
             flushExecutor.execute(flush);
-            postFlushExecutor.execute(flush.postFlushTask);
+            postFlushExecutor().execute(flush.postFlushTask);
             return flush.postFlushTask;
         }
     }
 
+    private ExecutorPlus postFlushExecutor()
+    {
+        return SchemaConstants.isLocalSystemKeyspace(getKeyspaceName()) && systemPostFlushExecutor != null
+               ? systemPostFlushExecutor
+               : postFlushExecutor;
+    }
+
     public void unloadCf()
     {
         if (keyspace.getMetadata().params.durableWrites && !memtableWritesAreDurable())  // need to clear dirty regions