[xray] Implement task lease table, logic for deciding when to reconstruct a task (#2497)

src/common/state/ray_config.h

@@ -18,6 +18,10 @@ class RayConfig {
 
   int64_t num_heartbeats_timeout() const { return num_heartbeats_timeout_; }
 
+  int64_t initial_reconstruction_timeout_milliseconds() const {
+    return initial_reconstruction_timeout_milliseconds_;
+  }
+
   int64_t get_timeout_milliseconds() const { return get_timeout_milliseconds_; }
 
   uint64_t max_lineage_size() const { return max_lineage_size_; }
@@ -111,6 +115,7 @@ class RayConfig {
       : ray_protocol_version_(0x0000000000000000),
         heartbeat_timeout_milliseconds_(100),
         num_heartbeats_timeout_(100),
+        initial_reconstruction_timeout_milliseconds_(200),
         get_timeout_milliseconds_(1000),
         worker_get_request_size_(10000),
         worker_fetch_request_size_(10000),
@@ -157,6 +162,12 @@ class RayConfig {
   /// it as dead to the db_client table.
   int64_t num_heartbeats_timeout_;
 
+  /// The initial period for a task execution lease. The lease will expire this
+  /// many milliseconds after the first acquisition of the lease. Nodes that
+  /// require an object will not try to reconstruct the task until at least
+  /// this many milliseconds.
+  int64_t initial_reconstruction_timeout_milliseconds_;
+
   /// These are used by the worker to set timeouts and to batch requests when
   /// getting objects.
   int64_t get_timeout_milliseconds_;