SERVER-70854 Code review comments

4 files changed, 123 insertions, 11 deletions

diff --git a/src/mongo/db/query/SConscript b/src/mongo/db/query/SConscript
index 4db9f6b6920..10dbd5ba849 100644
--- a/src/mongo/db/query/SConscript
+++ b/src/mongo/db/query/SConscript
@@ -261,6 +261,7 @@ env.Library(
         'query_feature_flags.idl',
         'query_knobs.idl',
         'sbe_plan_cache_on_parameter_change.cpp',
+        'telemetry_util.cpp',
     ],
     LIBDEPS_PRIVATE=[
         '$BUILD_DIR/mongo/db/server_base',
diff --git a/src/mongo/db/query/query_knobs.idl b/src/mongo/db/query/query_knobs.idl
index 171accf9c06..899dddc41c9 100644
--- a/src/mongo/db/query/query_knobs.idl
+++ b/src/mongo/db/query/query_knobs.idl
@@ -32,6 +32,7 @@ global:
     - "mongo/db/query/ce_mode_parameter.h"
     - "mongo/db/query/plan_cache_size_parameter.h"
     - "mongo/db/query/sbe_plan_cache_on_parameter_change.h"
+    - "mongo/db/query/telemetry_util.h"
     - "mongo/platform/atomic_proxy.h"
     - "mongo/platform/atomic_word.h"
 
@@ -946,22 +947,30 @@ server_parameters:
     default:
       expr: false
 
-  internalQueryConfigureTelemetryCacheSize:
-    description: "Knob to configure the maximum cache size for telemetry collection."
+  internalQueryConfigureTelemetrySamplingRate:
+    description: "The maximum number of queries per second that are sampled for query telemetry.
+      If the rate of queries goes above this number, then rate limiting will kick in, and any
+      further queries will not be sampled. The default is INT_MAX, effectively meaning that all
+      queries will be sampled. This can be set to 0 to turn telemetry off completely."
     set_at: [ startup, runtime ]
-    cpp_varname: "queryTelemetryCacheSize"
+    cpp_varname: "queryTelemetrySamplingRate"
     cpp_vartype: AtomicWord<int>
-    default: 5000
+    default: 2147483647
 
-  internalQueryConfigureTelemetrySamplingPercentage:
-    description: "Knob to configure the percentage of queries that are sampled for telemetry."
+  internalQueryConfigureTelemetryCacheSize:
+    description: "The maximum amount of memory that the system will allocate for the query telemetry
+      cache. This will accept values in either of the following formats:
+      1. <number>% indicates a percentage of the physical memory available to the process. E.g.: 15%.
+      2. <number>(MB|GB), indicates the amount of memory in MB or GB. E.g.: 1.5GB, 100MB.
+      The default value is 5%, which means 5% of the physical memory available to the process."
     set_at: [ startup, runtime ]
-    cpp_varname: "queryTelemetrySamplingPercentage"
-    cpp_vartype: AtomicDouble
-    default: 0.7
+    cpp_varname: "queryTelemetryCacheSize"
+    cpp_vartype: synchronized_value<std::string>
+    default: "5%"
+    on_update: telemetry_util::onTelemetryCacheSizeUpdate
     validator:
-        gt: 0.0
-        lte: 1.0
+      callback: telemetry_util::validateTelemetryCacheSize
+
 
 # Note for adding additional query knobs:
 #
diff --git a/src/mongo/db/query/telemetry_util.cpp b/src/mongo/db/query/telemetry_util.cpp
new file mode 100644
index 00000000000..cb410cf63a2
--- /dev/null
+++ b/src/mongo/db/query/telemetry_util.cpp
@@ -0,0 +1,52 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/query/telemetry_util.h"
+#include "mongo/db/query/plan_cache_size_parameter.h"
+
+namespace mongo {
+namespace telemetry_util {
+
+Status onTelemetryCacheSizeUpdate(const std::string& str) {
+    auto newSize = plan_cache_util::PlanCacheSizeParameter::parse(str);
+    if (!newSize.isOK()) {
+        return newSize.getStatus();
+    }
+
+    // TODO update telemetry cache size wherever it is stored
+
+    return Status::OK();
+}
+
+Status validateTelemetryCacheSize(const std::string& str, const boost::optional<TenantId>&) {
+    return plan_cache_util::PlanCacheSizeParameter::parse(str).getStatus();
+}
+
+}  // namespace telemetry_util
+}  // namespace mongo
diff --git a/src/mongo/db/query/telemetry_util.h b/src/mongo/db/query/telemetry_util.h
new file mode 100644
index 00000000000..719174edd32
--- /dev/null
+++ b/src/mongo/db/query/telemetry_util.h
@@ -0,0 +1,50 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/base/status.h"
+#include "mongo/db/service_context.h"
+
+namespace mongo {
+
+namespace telemetry_util {
+
+/**
+ * Callback called on a change of telemetryCacheSize parameter.
+ */
+Status onTelemetryCacheSizeUpdate(const std::string& str);
+
+/**
+ * Callback called on validation of telemetryCacheSize parameter.
+ */
+Status validateTelemetryCacheSize(const std::string& str, const boost::optional<TenantId>&);
+
+}  // namespace telemetry_util
+}  // namespace mongo