Initial spec changes for query stats feature

spec/_attachments/ic.did

@@ -170,6 +170,12 @@ service ic : {
       memory_size: nat;
       cycles: nat;
       idle_cycles_burned_per_day: nat;
+      query_stats: vec record {
+          num_calls: nat;
+          num_instructions: nat;
+          num_request_payload_bytes: nat;
+          num_response_payload_bytes: nat;
+      };
   });
   canister_info : (record {
       canister_id : canister_id;

spec/index.md

@@ -2038,6 +2038,16 @@ Indicates various information about the canister. It contains:
 
 -   The cycle balance of the canister.
 
+-   Statistics regarding the query execution of the canister, i.e., a record containing the following fields:
+
+    * `num_queries`: the total number of query calls evaluated on the canister,
+
+    * `num_instructions`: the total number of WebAssembly instructions executed during the evaluation of query calls on the canister,
+
+    * `num_request_payload_bytes`: the total number of query call request payload (query argument) bytes, and
+
+    * `num_response_payload_bytes`: the total number of query call response payload (reply data or reject message) bytes.
+
 Only the controllers of the canister or the canister itself can request its status.
 
 ### IC method `canister_info` {#ic-canister-info}
@@ -2908,6 +2918,12 @@ Finally, we can describe the state of the IC as a record having the following fi
       total_num_changes : Nat;
       recent_changes : [Change];
     }
+    QueryStats = {
+      timestamp : Timestamp;
+      num_instructions : Nat;
+      num_request_payload_bytes : Nat;
+      num_response_payload_bytes : Nat;
+    }
     Subnet = {
       subnet_id : Principal;
       subnet_size : Nat;
@@ -2927,6 +2943,7 @@ Finally, we can describe the state of the IC as a record having the following fi
       balances: CanisterId ↦ Nat;
       certified_data: CanisterId ↦ Blob;
       canister_history: CanisterId ↦ CanisterHistory;
+      query_stats: CanisterId ↦ [QueryStats];
       system_time : Timestamp
       call_contexts : CallId ↦ CallCtxt;
       messages : List Message; // ordered!
@@ -2972,6 +2989,7 @@ The initial state of the IC is
       balances = ();
       certified_data = ();
       canister_history = ();
+      query_stats = ();
       system_time = T;
       call_contexts = ();
       messages = [];
@@ -3728,6 +3746,7 @@ S with
     freezing_threshold[CanisterId] = New_freezing_threshold
     balances[CanisterId] = M.transferred_cycles
     certified_data[CanisterId] = ""
+    query_stats[CanisterId] = []
     canister_history[CanisterId] = New_canister_history
     messages = Older_messages · Younger_messages ·
       ResponseMessage {
@@ -3893,12 +3912,18 @@ S with
             S.freezing_threshold[A.canister_id],
             S.canister_subnet[A.canister_id].subnet_size,
           );
+          query_stats = noise(SUM {(1, num_instructions, num_request_payload_bytes, num_response_payload_bytes) |
+                                   (t, num_instructions, num_request_payload_bytes, num_response_payload_bytes) <- S.query_stats[A.canister_id]
+                                   t <= S.time[A.canister_id] - T})
         })
         refunded_cycles = M.transferred_cycles
       }
 
 ```
 
+where `T` is an unspecified time delay of query statistics and `noise` is an unspecified probabilistic function
+modelling information loss due to aggregating query statistics in a distributed system.
+
 #### IC Management Canister: Canister information
 
 Every canister can retrieve the canister history, current module hash, and current controllers of every other canister (including itself).
@@ -4605,6 +4630,7 @@ S with
     balances[A.canister_id] = (deleted)
     certified_data[A.canister_id] = (deleted)
     canister_history[A.canister_id] = (deleted)
+    query_stats[A.canister_id] = (deleted)
     messages = Older_messages · Younger_messages ·
       ResponseMessage {
         origin = M.origin
@@ -4757,6 +4783,7 @@ S with
     balances[Canister_id] = New_balance
     certified_data[Canister_id] = ""
     canister_history[Canister_id] = New_canister_history
+    query_stats[CanisterId] = []
     messages = Older_messages · Younger_messages ·
       ResponseMessage {
         origin = M.origin
@@ -5226,6 +5253,25 @@ verify_response(Q, R, Cert') ∧ lookup(["time"], Cert') = Found S.system_time /
 
 ```
 
+State after
+
+```html
+
+S with
+    query_stats[Q.receiver] = S.query_stats[Q.receiver] · {
+        timestamp = S.time[Q.receiver]
+        num_instructions = NumInstructions
+        num_request_payload_bytes = |Q.Arg|
+        num_response_payload_bytes =
+          if composite_query_helper(S, MAX_CYCLES_PER_QUERY, 0, Q.canister_id, Q.sender, Q.canister_id, Q.method_name, Q.arg) = (Reject (RejectCode, RejectMsg), _) then |RejectMsg|
+          else if composite_query_helper(S, MAX_CYCLES_PER_QUERY, 0, Q.canister_id, Q.sender, Q.canister_id, Q.method_name, Q.arg) = (Reply Res, _) then |Res|
+    }
+
+```
+
+where `NumInstructions` is the unspecified number of WebAssembly instructions executed during the evaluation of the query call,
+i.e., the value of `ic0.performance_counter(0)` at the end of the query method execution.
+
 #### Certified state reads
 
 :::note