SERVER-70854 Add telemetry infrastructure and generic memory size tools

12 files changed, 253 insertions, 122 deletions

diff --git a/src/mongo/db/query/SConscript b/src/mongo/db/query/SConscript
index 4db9f6b6920..a8e0d995716 100644
--- a/src/mongo/db/query/SConscript
+++ b/src/mongo/db/query/SConscript
@@ -100,6 +100,7 @@ env.Library(
     LIBDEPS=[
         "$BUILD_DIR/mongo/base",
         "$BUILD_DIR/mongo/db/exec/sbe/query_sbe",
+        '$BUILD_DIR/mongo/util/memory_util',
         "canonical_query",
     ],
 )
@@ -257,14 +258,15 @@ env.Library(
     source=[
         'ce_mode_parameter.cpp',
         'framework_control.cpp',
-        'plan_cache_size_parameter.cpp',
         'query_feature_flags.idl',
         'query_knobs.idl',
         'sbe_plan_cache_on_parameter_change.cpp',
+        'telemetry_util.cpp',
     ],
     LIBDEPS_PRIVATE=[
         '$BUILD_DIR/mongo/db/server_base',
         '$BUILD_DIR/mongo/db/service_context',
+        '$BUILD_DIR/mongo/util/memory_util',
         '$BUILD_DIR/mongo/util/pcre_wrapper',
     ],
 )
@@ -372,7 +374,6 @@ env.CppUnitTest(
         'map_reduce_output_format_test.cpp',
         "parsed_distinct_test.cpp",
         "plan_cache_indexability_test.cpp",
-        "plan_cache_size_parameter_test.cpp",
         "plan_cache_key_info_test.cpp",
         "plan_cache_test.cpp",
         "plan_ranker_test.cpp",
diff --git a/src/mongo/db/query/plan_cache_size_parameter_test.cpp b/src/mongo/db/query/plan_cache_size_parameter_test.cpp
deleted file mode 100644
index 1f0fbf76a27..00000000000
--- a/src/mongo/db/query/plan_cache_size_parameter_test.cpp
+++ /dev/null
@@ -1,79 +0,0 @@
-/**
- *    Copyright (C) 2021-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/plan_cache_size_parameter.h"
-
-#include "mongo/unittest/unittest.h"
-
-namespace mongo::plan_cache_util {
-
-bool operator==(const PlanCacheSizeParameter& lhs, const PlanCacheSizeParameter& rhs) {
-    constexpr double kEpsilon = 1e-10;
-    return std::abs(lhs.size - rhs.size) < kEpsilon && lhs.units == rhs.units;
-}
-
-TEST(PlanCacheParameterTest, ParseUnitStringPercent) {
-    ASSERT_TRUE(PlanCacheSizeUnits::kPercent == parseUnitString("%"));
-}
-
-TEST(PlanCacheParameterTest, ParseUnitStringMB) {
-    ASSERT_TRUE(PlanCacheSizeUnits::kMB == parseUnitString("MB"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kMB == parseUnitString("mb"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kMB == parseUnitString("mB"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kMB == parseUnitString("Mb"));
-}
-
-TEST(PlanCacheParameterTest, ParseUnitStringGB) {
-    ASSERT_TRUE(PlanCacheSizeUnits::kGB == parseUnitString("GB"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kGB == parseUnitString("gb"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kGB == parseUnitString("gB"));
-    ASSERT_TRUE(PlanCacheSizeUnits::kGB == parseUnitString("Gb"));
-}
-
-TEST(PlanCacheParameterTest, ParseUnitStringIncorrectValue) {
-    ASSERT_NOT_OK(parseUnitString("").getStatus());
-    ASSERT_NOT_OK(parseUnitString(" ").getStatus());
-    ASSERT_NOT_OK(parseUnitString("KB").getStatus());
-}
-
-TEST(PlanCacheParameterTest, ParsePlanCacheSizeParameter) {
-    ASSERT_TRUE((PlanCacheSizeParameter{10.0, PlanCacheSizeUnits::kPercent}) ==
-                PlanCacheSizeParameter::parse("10%"));
-    ASSERT_TRUE((PlanCacheSizeParameter{300.0, PlanCacheSizeUnits::kMB}) ==
-                PlanCacheSizeParameter::parse("300MB"));
-    ASSERT_TRUE((PlanCacheSizeParameter{4.0, PlanCacheSizeUnits::kGB}) ==
-                PlanCacheSizeParameter::parse("4GB"));
-    ASSERT_TRUE((PlanCacheSizeParameter{5.1, PlanCacheSizeUnits::kPercent}) ==
-                PlanCacheSizeParameter::parse(" 5.1%"));
-    ASSERT_TRUE((PlanCacheSizeParameter{11.1, PlanCacheSizeUnits::kMB}) ==
-                PlanCacheSizeParameter::parse("11.1 mb"));
-    ASSERT_TRUE((PlanCacheSizeParameter{12.1, PlanCacheSizeUnits::kGB}) ==
-                PlanCacheSizeParameter::parse("  12.1    Gb  "));
-}
-}  // namespace mongo::plan_cache_util
diff --git a/src/mongo/db/query/query_knobs.idl b/src/mongo/db/query/query_knobs.idl
index 1a7423a9a12..0584ec15b69 100644
--- a/src/mongo/db/query/query_knobs.idl
+++ b/src/mongo/db/query/query_knobs.idl
@@ -30,8 +30,8 @@ global:
   cpp_namespace: "mongo"
   cpp_includes:
     - "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"
 
@@ -948,6 +948,31 @@ server_parameters:
     default: false
     test_only: true
 
+  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: "queryTelemetrySamplingRate"
+    cpp_vartype: AtomicWord<int>
+    default: 2147483647
+
+  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: "queryTelemetryCacheSize"
+    cpp_vartype: synchronized_value<std::string>
+    default: "5%"
+    on_update: telemetry_util::onTelemetryCacheSizeUpdate
+    validator:
+      callback: telemetry_util::validateTelemetryCacheSize
+
+
 # Note for adding additional query knobs:
 #
 # When adding a new query knob, you should consider whether or not you need to add an 'on_update'
diff --git a/src/mongo/db/query/sbe_plan_cache.cpp b/src/mongo/db/query/sbe_plan_cache.cpp
index fc267726f64..18d8b9fc5c9 100644
--- a/src/mongo/db/query/sbe_plan_cache.cpp
+++ b/src/mongo/db/query/sbe_plan_cache.cpp
@@ -30,9 +30,9 @@
 
 #include "mongo/db/query/sbe_plan_cache.h"
 
-#include "mongo/db/query/plan_cache_size_parameter.h"
 #include "mongo/db/server_options.h"
 #include "mongo/logv2/log.h"
+#include "mongo/util/memory_util.h"
 #include "mongo/util/processinfo.h"
 
 #define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kQuery
@@ -44,19 +44,19 @@ namespace {
 const auto sbePlanCacheDecoration =
     ServiceContext::declareDecoration<std::unique_ptr<sbe::PlanCache>>();
 
-size_t convertToSizeInBytes(const plan_cache_util::PlanCacheSizeParameter& param) {
+size_t convertToSizeInBytes(const memory_util::MemorySize& memSize) {
     constexpr size_t kBytesInMB = 1024 * 1024;
     constexpr size_t kMBytesInGB = 1024;
 
-    double sizeInMB = param.size;
+    double sizeInMB = memSize.size;
 
-    switch (param.units) {
-        case plan_cache_util::PlanCacheSizeUnits::kPercent:
+    switch (memSize.units) {
+        case memory_util::MemoryUnits::kPercent:
             sizeInMB *= ProcessInfo::getMemSizeMB() / 100.0;
             break;
-        case plan_cache_util::PlanCacheSizeUnits::kMB:
+        case memory_util::MemoryUnits::kMB:
             break;
-        case plan_cache_util::PlanCacheSizeUnits::kGB:
+        case memory_util::MemoryUnits::kGB:
             sizeInMB *= kMBytesInGB;
             break;
     }
@@ -75,8 +75,7 @@ size_t capPlanCacheSize(size_t planCacheSize) {
     constexpr size_t kMaximumPlanCacheSize = 500 * kBytesInGB;
 
     // Maximum size of the plan cache expressed as a share of the memory available to the process.
-    const plan_cache_util::PlanCacheSizeParameter limitToProcessSize{
-        25, plan_cache_util::PlanCacheSizeUnits::kPercent};
+    const memory_util::MemorySize limitToProcessSize{25, memory_util::MemoryUnits::kPercent};
     const size_t limitToProcessSizeInBytes = convertToSizeInBytes(limitToProcessSize);
 
     // The size will be capped by the minimum of the two values defined above.
@@ -93,8 +92,8 @@ size_t capPlanCacheSize(size_t planCacheSize) {
     return planCacheSize;
 }
 
-size_t getPlanCacheSizeInBytes(const plan_cache_util::PlanCacheSizeParameter& param) {
-    size_t planCacheSize = convertToSizeInBytes(param);
+size_t getPlanCacheSizeInBytes(const memory_util::MemorySize& memSize) {
+    size_t planCacheSize = convertToSizeInBytes(memSize);
     uassert(5968001,
             "Cache size must be at least 1KB * number of cores",
             planCacheSize >= 1024 * ProcessInfo::getNumCores());
@@ -103,10 +102,9 @@ size_t getPlanCacheSizeInBytes(const plan_cache_util::PlanCacheSizeParameter& pa
 
 class PlanCacheOnParamChangeUpdaterImpl final : public plan_cache_util::OnParamChangeUpdater {
 public:
-    void updateCacheSize(ServiceContext* serviceCtx,
-                         plan_cache_util::PlanCacheSizeParameter parameter) final {
+    void updateCacheSize(ServiceContext* serviceCtx, memory_util::MemorySize memSize) final {
         if (feature_flags::gFeatureFlagSbeFull.isEnabledAndIgnoreFCV()) {
-            auto size = getPlanCacheSizeInBytes(parameter);
+            auto size = getPlanCacheSizeInBytes(memSize);
             auto& globalPlanCache = sbePlanCacheDecoration(serviceCtx);
             globalPlanCache->reset(size);
         }
@@ -126,7 +124,7 @@ ServiceContext::ConstructorActionRegisterer planCacheRegisterer{
             std::make_unique<PlanCacheOnParamChangeUpdaterImpl>();
 
         if (feature_flags::gFeatureFlagSbeFull.isEnabledAndIgnoreFCV()) {
-            auto status = plan_cache_util::PlanCacheSizeParameter::parse(planCacheSize.get());
+            auto status = memory_util::MemorySize::parse(planCacheSize.get());
             uassertStatusOK(status);
 
             auto size = getPlanCacheSizeInBytes(status.getValue());
diff --git a/src/mongo/db/query/sbe_plan_cache_on_parameter_change.cpp b/src/mongo/db/query/sbe_plan_cache_on_parameter_change.cpp
index b7ea17858d8..5854cea3c57 100644
--- a/src/mongo/db/query/sbe_plan_cache_on_parameter_change.cpp
+++ b/src/mongo/db/query/sbe_plan_cache_on_parameter_change.cpp
@@ -56,7 +56,7 @@ Status clearSbeCacheOnParameterChangeHelper() {
 }
 
 Status onPlanCacheSizeUpdate(const std::string& str) {
-    auto newSize = PlanCacheSizeParameter::parse(str);
+    auto newSize = memory_util::MemorySize::parse(str);
     if (!newSize.isOK()) {
         return newSize.getStatus();
     }
@@ -73,7 +73,7 @@ Status onPlanCacheSizeUpdate(const std::string& str) {
 }
 
 Status validatePlanCacheSize(const std::string& str, const boost::optional<TenantId>&) {
-    return PlanCacheSizeParameter::parse(str).getStatus();
+    return memory_util::MemorySize::parse(str).getStatus();
 }
 
 const Decorable<ServiceContext>::Decoration<std::unique_ptr<OnParamChangeUpdater>>
diff --git a/src/mongo/db/query/sbe_plan_cache_on_parameter_change.h b/src/mongo/db/query/sbe_plan_cache_on_parameter_change.h
index fd7f090d766..4135bb7f2b9 100644
--- a/src/mongo/db/query/sbe_plan_cache_on_parameter_change.h
+++ b/src/mongo/db/query/sbe_plan_cache_on_parameter_change.h
@@ -32,8 +32,8 @@
 #include <string>
 
 #include "mongo/base/status.h"
-#include "mongo/db/query/plan_cache_size_parameter.h"
 #include "mongo/db/service_context.h"
+#include "mongo/util/memory_util.h"
 
 namespace mongo::plan_cache_util {
 
@@ -70,11 +70,11 @@ public:
     virtual ~OnParamChangeUpdater() = default;
 
     /**
-     * Resizes the SBE plan cache decorating 'serviceCtx' to the new size given by 'parameter'. If
+     * Resizes the SBE plan cache decorating 'serviceCtx' to the new size given by 'memSize'. If
      * the new cache size is smaller than the old, cache entries are evicted in order to ensure the
      * cache fits within the new size bound.
      */
-    virtual void updateCacheSize(ServiceContext* serviceCtx, PlanCacheSizeParameter parameter) = 0;
+    virtual void updateCacheSize(ServiceContext* serviceCtx, memory_util::MemorySize memSize) = 0;
 
     /**
      * Deletes all plans from the SBE plan cache decorating 'serviceCtx'.
diff --git a/src/mongo/db/query/telemetry_util.cpp b/src/mongo/db/query/telemetry_util.cpp
new file mode 100644
index 00000000000..8e3f6f6361d
--- /dev/null
+++ b/src/mongo/db/query/telemetry_util.cpp
@@ -0,0 +1,52 @@
+/**
+ *    Copyright (C) 2022-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/util/memory_util.h"
+
+namespace mongo {
+namespace telemetry_util {
+
+Status onTelemetryCacheSizeUpdate(const std::string& str) {
+    auto newSize = memory_util::MemorySize::parse(str);
+    if (!newSize.isOK()) {
+        return newSize.getStatus();
+    }
+
+    // TODO SERVER-71065 update telemetry cache size
+
+    return Status::OK();
+}
+
+Status validateTelemetryCacheSize(const std::string& str, const boost::optional<TenantId>&) {
+    return memory_util::MemorySize::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..a55ca035d74
--- /dev/null
+++ b/src/mongo/db/query/telemetry_util.h
@@ -0,0 +1,50 @@
+/**
+ *    Copyright (C) 2022-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
diff --git a/src/mongo/util/SConscript b/src/mongo/util/SConscript
index e90c9ffb348..1ba28162068 100644
--- a/src/mongo/util/SConscript
+++ b/src/mongo/util/SConscript
@@ -614,6 +614,16 @@ env.Library(
     ],
 )
 
+env.Library(
+    target='memory_util',
+    source=[
+        'memory_util.cpp',
+    ],
+    LIBDEPS=[
+        'pcre_wrapper',
+    ],
+)
+
 env.Benchmark(
     target='hash_table_bm',
     source='hash_table_bm.cpp',
@@ -748,6 +758,7 @@ icuEnv.CppUnitTest(
         'lru_cache_test.cpp',
         'md5_test.cpp',
         'md5main.cpp',
+        'memory_util_test.cpp',
         'optional_util_test.cpp',
         'out_of_line_executor_test.cpp',
         'overloaded_visitor_test.cpp',
@@ -795,6 +806,7 @@ icuEnv.CppUnitTest(
         'icu',
         'latch_analyzer' if get_option('use-diagnostic-latches') == 'on' else [],
         'md5',
+        'memory_util',
         'pcre_util',
         'pcre_wrapper',
         'periodic_runner_impl',
diff --git a/src/mongo/db/query/plan_cache_size_parameter.cpp b/src/mongo/util/memory_util.cpp
index 5f1f66bcaf8..28b5822c508 100644
--- a/src/mongo/db/query/plan_cache_size_parameter.cpp
+++ b/src/mongo/util/memory_util.cpp
@@ -27,35 +27,34 @@
  *    it in the license file.
  */
 
-#include "mongo/db/query/plan_cache_size_parameter.h"
+#include "mongo/util/memory_util.h"
 
-#include "mongo/db/query/query_knobs_gen.h"
 #include "mongo/util/pcre.h"
 
-namespace mongo::plan_cache_util {
+namespace mongo::memory_util {
 
-StatusWith<PlanCacheSizeUnits> parseUnitString(const std::string& strUnit) {
+StatusWith<MemoryUnits> parseUnitString(const std::string& strUnit) {
     if (strUnit.empty()) {
         return Status(ErrorCodes::Error{6007010}, "Unit value cannot be empty");
     }
 
     if (strUnit[0] == '%') {
-        return PlanCacheSizeUnits::kPercent;
+        return MemoryUnits::kPercent;
     } else if (strUnit[0] == 'M' || strUnit[0] == 'm') {
-        return PlanCacheSizeUnits::kMB;
+        return MemoryUnits::kMB;
     } else if (strUnit[0] == 'G' || strUnit[0] == 'g') {
-        return PlanCacheSizeUnits::kGB;
+        return MemoryUnits::kGB;
     }
 
     return Status(ErrorCodes::Error{6007011}, "Incorrect unit value");
 }
 
-StatusWith<PlanCacheSizeParameter> PlanCacheSizeParameter::parse(const std::string& str) {
+StatusWith<MemorySize> MemorySize::parse(const std::string& str) {
     // Looks for a floating point number with followed by a unit suffix (MB, GB, %).
     static auto& re = *new pcre::Regex(R"re((?i)^\s*(\d+\.?\d*)\s*(MB|GB|%)\s*$)re");
     auto m = re.matchView(str);
     if (!m) {
-        return {ErrorCodes::Error{6007012}, "Unable to parse plan cache size string"};
+        return {ErrorCodes::Error{6007012}, "Unable to parse memory size string"};
     }
     double size = std::stod(std::string{m[1]});
     std::string strUnit{m[2]};
@@ -65,7 +64,7 @@ StatusWith<PlanCacheSizeParameter> PlanCacheSizeParameter::parse(const std::stri
         return statusWithUnit.getStatus();
     }
 
-    return PlanCacheSizeParameter{size, statusWithUnit.getValue()};
+    return MemorySize{size, statusWithUnit.getValue()};
 }
 
-}  // namespace mongo::plan_cache_util
+}  // namespace mongo::memory_util
diff --git a/src/mongo/db/query/plan_cache_size_parameter.h b/src/mongo/util/memory_util.h
index 322a1fff564..d1452dbfee9 100644
--- a/src/mongo/db/query/plan_cache_size_parameter.h
+++ b/src/mongo/util/memory_util.h
@@ -33,27 +33,27 @@
 
 #include "mongo/base/status_with.h"
 
-namespace mongo::plan_cache_util {
+namespace mongo::memory_util {
 
 /**
- * Defines units of planCacheSize parameter.
+ * Defines units of memory.
  */
-enum class PlanCacheSizeUnits {
+enum class MemoryUnits {
     kPercent,
     kMB,
     kGB,
 };
 
-StatusWith<PlanCacheSizeUnits> parseUnitString(const std::string& strUnit);
+StatusWith<MemoryUnits> parseUnitString(const std::string& strUnit);
 
 /**
- * Represents parsed planCacheSize parameter.
+ * Represents parsed memory size parameter.
  */
-struct PlanCacheSizeParameter {
-    static StatusWith<PlanCacheSizeParameter> parse(const std::string& str);
+struct MemorySize {
+    static StatusWith<MemorySize> parse(const std::string& str);
 
     const double size;
-    const PlanCacheSizeUnits units;
+    const MemoryUnits units;
 };
 
-}  // namespace mongo::plan_cache_util
+}  // namespace mongo::memory_util
diff --git a/src/mongo/util/memory_util_test.cpp b/src/mongo/util/memory_util_test.cpp
new file mode 100644
index 00000000000..d19ca82e89a
--- /dev/null
+++ b/src/mongo/util/memory_util_test.cpp
@@ -0,0 +1,73 @@
+/**
+ *    Copyright (C) 2021-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/util/memory_util.h"
+
+#include "mongo/unittest/unittest.h"
+
+namespace mongo::memory_util {
+
+bool operator==(const MemorySize& lhs, const MemorySize& rhs) {
+    constexpr double kEpsilon = 1e-10;
+    return std::abs(lhs.size - rhs.size) < kEpsilon && lhs.units == rhs.units;
+}
+
+TEST(MemorySizeTest, ParseUnitStringPercent) {
+    ASSERT_TRUE(MemoryUnits::kPercent == parseUnitString("%"));
+}
+
+TEST(MemorySizeTest, ParseUnitStringMB) {
+    ASSERT_TRUE(MemoryUnits::kMB == parseUnitString("MB"));
+    ASSERT_TRUE(MemoryUnits::kMB == parseUnitString("mb"));
+    ASSERT_TRUE(MemoryUnits::kMB == parseUnitString("mB"));
+    ASSERT_TRUE(MemoryUnits::kMB == parseUnitString("Mb"));
+}
+
+TEST(MemorySizeTest, ParseUnitStringGB) {
+    ASSERT_TRUE(MemoryUnits::kGB == parseUnitString("GB"));
+    ASSERT_TRUE(MemoryUnits::kGB == parseUnitString("gb"));
+    ASSERT_TRUE(MemoryUnits::kGB == parseUnitString("gB"));
+    ASSERT_TRUE(MemoryUnits::kGB == parseUnitString("Gb"));
+}
+
+TEST(MemorySizeTest, ParseUnitStringIncorrectValue) {
+    ASSERT_NOT_OK(parseUnitString("").getStatus());
+    ASSERT_NOT_OK(parseUnitString(" ").getStatus());
+    ASSERT_NOT_OK(parseUnitString("KB").getStatus());
+}
+
+TEST(MemorySizeTest, ParseMemorySize) {
+    ASSERT_TRUE((MemorySize{10.0, MemoryUnits::kPercent}) == MemorySize::parse("10%"));
+    ASSERT_TRUE((MemorySize{300.0, MemoryUnits::kMB}) == MemorySize::parse("300MB"));
+    ASSERT_TRUE((MemorySize{4.0, MemoryUnits::kGB}) == MemorySize::parse("4GB"));
+    ASSERT_TRUE((MemorySize{5.1, MemoryUnits::kPercent}) == MemorySize::parse(" 5.1%"));
+    ASSERT_TRUE((MemorySize{11.1, MemoryUnits::kMB}) == MemorySize::parse("11.1 mb"));
+    ASSERT_TRUE((MemorySize{12.1, MemoryUnits::kGB}) == MemorySize::parse("  12.1    Gb  "));
+}
+}  // namespace mongo::memory_util