XRay Task Forwarding Milestone (#1785)

Summary:
Able to run 1000 tasks with object dependencies on a set of distributed Raylets.

Raylet Changes:

Finalized ClientConnection class.
Task forwarding.
NM-to-NM heartbeats.
NM resource accounting for tasks.
Simple scheduling policy with task forwarding.
Creating and maintaining NM 2 NM long-lived connections and reusing them for task forwarding.
LineageCache Changes:

LineageCache without cleanup of tasks committed by remote nodes.
Lineage cache writeback and cleanup implementation.
ObjectManager Changes:

Object manager event loop/ClientConnection refactor.
Multithreaded object manager (disabled in this PR).
Testing Changes:

Integration tests for task submission on multiple Raylets.
Stress tests for object manager (with GCS and object store integration).


Co-authored-by: Stephanie Wang <swang@cs.berkeley.edu>
Co-authored-by: Alexey Tumanov <atumanov@gmail.com>

src/common/redis_module/ray_redis_module.cc

@@ -50,7 +50,14 @@
   }
 
 static const char *table_prefixes[] = {
-    NULL, "TASK:", "TASK:", "CLIENT:", "OBJECT:", "FUNCTION:",
+    NULL,
+    "TASK:",
+    "TASK:",
+    "CLIENT:",
+    "OBJECT:",
+    "FUNCTION:",
+    "TASK_RECONSTRUCTION:",
+    "HEARTBEAT:",
 };
 
 /// Parse a Redis string into a TablePubsub channel.
@@ -811,8 +818,9 @@ int TableRequestNotifications_RedisCommand(RedisModuleCtx *ctx,
     // notifications.
     flatbuffers::FlatBufferBuilder fbb;
     TableEntryToFlatbuf(table_key, id, fbb);
-    RedisModule_Call(ctx, "PUBLISH", "sb", client_channel, reinterpret_cast<const char *>(fbb.GetBufferPointer()),
-        fbb.GetSize());
+    RedisModule_Call(ctx, "PUBLISH", "sb", client_channel,
+                     reinterpret_cast<const char *>(fbb.GetBufferPointer()),
+                     fbb.GetSize());
   }
   RedisModule_CloseKey(table_key);