Add histograms for HintCacheLevelDBStore

UMA histograms have been added to HintCacheLevelDBStore for tracking the result
of loading the metadata and for tracking status changes within the store.

Change-Id: Iac6cbb37284e48a557469c0fcb13e57f33f97599
Reviewed-on: https://chromium-review.googlesource.com/c/1432893Reviewed-by: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Commit-Queue: Jered Gray <jegray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625842}

components/previews/content/hint_cache_leveldb_store.cc

@@ -4,6 +4,7 @@
 
 #include "components/previews/content/hint_cache_leveldb_store.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "components/leveldb_proto/public/proto_database_provider.h"
 
 namespace previews {
@@ -28,6 +29,43 @@ constexpr size_t kDatabaseWriteBufferSizeBytes = 128 * 1024;
 //    "[EntryType::kComponentHint]_[component_version]_[host]"
 constexpr char kKeySectionDelimiter = '_';
 
+// Enumerates the possible outcomes of loading metadata. Used in UMA histograms,
+// so the order of enumerators should not be changed.
+//
+// Keep in sync with PreviewsHintCacheLevelDBStoreProcessMetadataResult in
+// tools/metrics/histograms/enums.xml.
+enum class PreviewsHintCacheLevelDBStoreLoadMetadataResult {
+  kSuccess = 0,
+  kLoadMetadataFailed = 1,
+  kSchemaMetadataMissing = 2,
+  kSchemaMetadataWrongVersion = 3,
+  kComponentMetadataMissing = 4,
+  kMaxValue = kComponentMetadataMissing,
+};
+
+// Util class for recording the result of loading the metadata. The result is
+// recorded when it goes out of scope and its destructor is called.
+class ScopedLoadMetadataResultRecorder {
+ public:
+  ScopedLoadMetadataResultRecorder()
+      : result_(PreviewsHintCacheLevelDBStoreLoadMetadataResult::kSuccess) {}
+  ~ScopedLoadMetadataResultRecorder() {
+    UMA_HISTOGRAM_ENUMERATION(
+        "Previews.HintCacheLevelDBStore.LoadMetadataResult", result_);
+  }
+
+  void set_result(PreviewsHintCacheLevelDBStoreLoadMetadataResult result) {
+    result_ = result;
+  }
+
+ private:
+  PreviewsHintCacheLevelDBStoreLoadMetadataResult result_;
+};
+
+void RecordStatusChange(HintCacheLevelDBStore::Status status) {
+  UMA_HISTOGRAM_ENUMERATION("Previews.HintCacheLevelDBStore.Status", status);
+}
+
 }  // namespace
 
 HintCacheLevelDBStore::HintCacheLevelDBStore(
@@ -46,7 +84,9 @@ HintCacheLevelDBStore::HintCacheLevelDBStore(
       database_(std::move(database)),
       status_(Status::kUninitialized),
       component_data_update_in_flight_(false),
-      weak_ptr_factory_(this) {}
+      weak_ptr_factory_(this) {
+  RecordStatusChange(status_);
+}
 
 HintCacheLevelDBStore::~HintCacheLevelDBStore() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
@@ -268,15 +308,16 @@ void HintCacheLevelDBStore::UpdateStatus(Status new_status) {
   // The status can never transition from Status::kFailed.
   DCHECK(status_ != Status::kFailed || new_status == Status::kFailed);
 
-  // If the database transitions into a failed state from a non-failed state,
-  // then fully destroy it. This ensures that it'll have a clean state the next
-  // time it is created.
-  bool destroy_database =
-      status_ != Status::kFailed && new_status == Status::kFailed;
+  // If the status is not changing, simply return; the remaining logic handles
+  // status changes.
+  if (status_ == new_status) {
+    return;
+  }
 
   status_ = new_status;
+  RecordStatusChange(status_);
 
-  if (destroy_database) {
+  if (status_ == Status::kFailed) {
     database_->Destroy(
         base::BindOnce(&HintCacheLevelDBStore::OnDatabaseDestroyed,
                        weak_ptr_factory_.GetWeakPtr()));
@@ -401,7 +442,14 @@ void HintCacheLevelDBStore::OnLoadMetadata(
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   DCHECK(metadata_entries);
 
+  // Create a scoped load metadata result recorder. It records the result when
+  // its destructor is called.
+  ScopedLoadMetadataResultRecorder result_recorder;
+
   if (!success) {
+    result_recorder.set_result(
+        PreviewsHintCacheLevelDBStoreLoadMetadataResult::kLoadMetadataFailed);
+
     UpdateStatus(Status::kFailed);
     std::move(callback).Run();
     return;
@@ -414,6 +462,16 @@ void HintCacheLevelDBStore::OnLoadMetadata(
   if (schema_entry == metadata_entries->end() ||
       !schema_entry->second.has_version() ||
       schema_entry->second.version() != kStoreSchemaVersion) {
+    if (schema_entry == metadata_entries->end()) {
+      result_recorder.set_result(
+          PreviewsHintCacheLevelDBStoreLoadMetadataResult::
+              kSchemaMetadataMissing);
+    } else {
+      result_recorder.set_result(
+          PreviewsHintCacheLevelDBStoreLoadMetadataResult::
+              kSchemaMetadataWrongVersion);
+    }
+
     PurgeDatabase(std::move(callback));
     return;
   }
@@ -425,6 +483,9 @@ void HintCacheLevelDBStore::OnLoadMetadata(
   if (component_entry != metadata_entries->end()) {
     DCHECK(component_entry->second.has_version());
     SetComponentVersion(base::Version(component_entry->second.version()));
+  } else {
+    result_recorder.set_result(PreviewsHintCacheLevelDBStoreLoadMetadataResult::
+                                   kComponentMetadataMissing);
   }
 
   UpdateStatus(Status::kAvailable);

components/previews/content/hint_cache_leveldb_store.h

@@ -33,6 +33,22 @@ class HintCacheLevelDBStore : public HintCacheStore {
   using StoreEntryProtoDatabase =
       leveldb_proto::ProtoDatabase<previews::proto::StoreEntry>;
 
+  // Status of the store. The store begins in kUninitialized, transitions to
+  // kInitializing after Initialize() is called, and transitions to kAvailable
+  // if initialization successfully completes. In the case where anything fails,
+  // the store transitions to kFailed, at which point it is fully purged and
+  // becomes unusable.
+  //
+  // Keep in sync with PreviewsHintCacheLevelDBStoreStatus in
+  // tools/metrics/histograms/enums.xml.
+  enum class Status {
+    kUninitialized = 0,
+    kInitializing = 1,
+    kAvailable = 2,
+    kFailed = 3,
+    kMaxValue = kFailed,
+  };
+
   HintCacheLevelDBStore(
       const base::FilePath& database_dir,
       scoped_refptr<base::SequencedTaskRunner> store_task_runner);
@@ -66,18 +82,6 @@ class HintCacheLevelDBStore : public HintCacheStore {
       leveldb_proto::ProtoDatabase<previews::proto::StoreEntry>::KeyEntryVector;
   using EntryMap = std::map<EntryKey, previews::proto::StoreEntry>;
 
-  // Status of the store. The store begins in kUninitialized, transitions to
-  // kInitializing after Initialize() is called, and transitions to kAvailable
-  // if initialization successfully completes. In the case where anything fails,
-  // the store transitions to kFailed, at which point it is fully purged and
-  // becomes unusable.
-  enum class Status {
-    kUninitialized,
-    kInitializing,
-    kAvailable,
-    kFailed,
-  };
-
   // Entry types within the store appear at the start of the keys of entries.
   // These values are converted into strings within the key: a key starting with
   // "1_" signifies a metadata entry and one starting with "2_" signifies a

tools/metrics/histograms/enums.xml

@@ -43377,6 +43377,21 @@ Called by update_net_trust_anchors.py.-->
   <int value="15" label="Device was reported as offline."/>
 </enum>
 
+<enum name="PreviewsHintCacheLevelDBStoreLoadMetadataResult">
+  <int value="0" label="Success"/>
+  <int value="1" label="LoadMetadataFailed"/>
+  <int value="2" label="SchemaMetadataMissing"/>
+  <int value="3" label="SchemaMetadataWrongVersion"/>
+  <int value="4" label="ComponentMetadataMissing"/>
+</enum>
+
+<enum name="PreviewsHintCacheLevelDBStoreStatus">
+  <int value="0" label="Unitialized"/>
+  <int value="1" label="Initializing"/>
+  <int value="2" label="Available"/>
+  <int value="3" label="Failed"/>
+</enum>
+
 <enum name="PreviewsInfoBarAction">
   <int value="0" label="Infobar shown"/>
   <int value="1" label="Infobar 'Load original' clicked"/>

tools/metrics/histograms/histograms.xml

@@ -88146,6 +88146,23 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Previews.HintCacheLevelDBStore.LoadMetadataResult"
+    enum="PreviewsHintCacheLevelDBStoreLoadMetadataResult">
+  <owner>jegray@chromium.org</owner>
+  <summary>
+    Records the result of loading the metadata while initializing the
+    HintCacheLevelDBStore.
+  </summary>
+</histogram>
+
+<histogram name="Previews.HintCacheLevelDBStore.Status"
+    enum="PreviewsHintCacheLevelDBStoreStatus">
+  <owner>jegray@chromium.org</owner>
+  <summary>
+    Records each status change within the HintCacheLevelDBStore.
+  </summary>
+</histogram>
+
 <histogram name="Previews.InfoBarAction" enum="PreviewsInfoBarAction">
   <owner>bengr@chromium.org</owner>
   <owner>tbansal@chromium.org</owner>