Precache tracking database

components/precache/core/precache_database.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/precache/core/precache_database.h"
+
+#include "base/metrics/histogram.h"
+#include "base/time/time.h"
+#include "components/precache/core/precache_statistics_table.h"
+#include "components/precache/core/precache_url_table.h"
+#include "sql/connection.h"
+#include "url/gurl.h"
+
+namespace {
+
+// The number of days old that an entry in the precache URL table can be before
+// it is considered "old" and is removed from the table.
+const int64 kPrecacheHistoryExpiryPeriodDays = 60;
+
+void RecordSingleDayPrecacheUMA(
+    const precache::PrecacheStatisticsTable::PrecacheStatistics& stats) {
+  UMA_HISTOGRAM_COUNTS("Precache.DailyDownloadedPrecacheMotivatedKB",
+                       stats.downloaded_precache_motivated_bytes / 1024);
+  UMA_HISTOGRAM_COUNTS("Precache.DailyDownloadedNonPrecacheKB",
+                       stats.downloaded_non_precache_bytes / 1024);
+  UMA_HISTOGRAM_COUNTS("Precache.DailyDownloadedNonPrecacheKB.Cellular",
+                       stats.downloaded_non_precache_bytes_cellular / 1024);
+  UMA_HISTOGRAM_COUNTS("Precache.DailySavedKB", stats.saved_bytes / 1024);
+  UMA_HISTOGRAM_COUNTS("Precache.DailySavedKB.Cellular",
+                       stats.saved_bytes_cellular / 1024);
+
+  if (stats.saved_bytes + stats.downloaded_non_precache_bytes > 0) {
+    UMA_HISTOGRAM_PERCENTAGE(
+        "Precache.DailySavingsPercentage",
+        stats.saved_bytes * 100.0 /
+            (stats.saved_bytes + stats.downloaded_non_precache_bytes));
+  }
+
+  if (stats.saved_bytes_cellular +
+          stats.downloaded_non_precache_bytes_cellular > 0) {
+    UMA_HISTOGRAM_PERCENTAGE(
+        "Precache.DailySavingsPercentage.Cellular",
+        stats.saved_bytes_cellular * 100.0 /
+            (stats.saved_bytes_cellular +
+             stats.downloaded_non_precache_bytes_cellular));
+  }
+}
+
+}  // namespace
+
+namespace precache {
+
+PrecacheDatabase::PrecacheDatabase()
+    : precache_url_table_(new PrecacheURLTable()),
+      precache_statistics_table_(new PrecacheStatisticsTable()) {
+  // A PrecacheDatabase can be constructed on any thread.
+  DetachFromThread();
+}
+
+PrecacheDatabase::~PrecacheDatabase() {
+  // Since the PrecacheDatabase is refcounted, it will only be deleted if there
+  // are no references remaining to it, meaning that it is not in use. Thus, it
+  // is safe to delete it, regardless of what thread we are on.
+  DetachFromThread();
+}
+
+void PrecacheDatabase::Init(scoped_ptr<sql::Connection> db) {

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

I'm not seeing where this database is coming from originally?

[sclittle, 2013/11/19 23:27:10]

There will be a PrecacheManager BrowserContextKeyedService that will pass in the
database as a scoped pointer. The reason we don't create the database here is
because we want the database file to be stored on the BrowserContext's path,
which only the PrecacheManager will have access to.

[Scott Hess - ex-Googler, 2013/11/27 01:32:33]

But why does the caller create the database, as opposed to passing in the path?

[sclittle, 2013/12/02 21:12:52]

Good point. Changed this to take in a path instead.

+  DCHECK(CalledOnValidThread());
+  DCHECK(!db_);  // Init must only be called once.
+  DCHECK(db);    // |db| must not be NULL.
+

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

sql::Connection has a set_histogram_tag() which interfaces with
"SqliteDatabases" fieldtrial in histograms.xml to provide error and size
tracking.  This would be a reasonable place to set that up.

[sclittle, 2013/11/19 23:27:10]

Done.

+  db_ = db.Pass();
+  if (!IsDatabaseAccessible()) {
+    // Don't initialize the URL table or statistics table if unable to access
+    // the database.
+    return;
+  }
+
+  precache_url_table_->Init(db_.get());
+  precache_statistics_table_->Init(db_.get());

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

These should probably be in a transaction.

[sclittle, 2013/11/19 23:27:10]

Done.

+}
+
+void PrecacheDatabase::ReportAndDeleteOldStats(const base::Time& current_time) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(db_);

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

These are implicit in IsDatabaseAccessible().

[sclittle, 2013/11/19 23:27:10]

Done.

+
+  if (!IsDatabaseAccessible()) {
+    // Do nothing if unable to access the database.
+    return;
+  }
+

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

You should probably start a transaction here to encompass the following changes.

[sclittle, 2013/11/19 23:27:10]

Done.

+  // Delete old precache history that has expired.
+  precache_url_table_->DeleteAllPrecachedBefore(
+      current_time -
+      base::TimeDelta::FromDays(kPrecacheHistoryExpiryPeriodDays));
+
+  PrecacheStatisticsTable::PrecacheStatisticsMap stats_map;
+  precache_statistics_table_->GetOldStats(current_time, &stats_map);
+
+  // Report UMA for every row of old statistics in the statistics table. There
+  // won't be any rows in the statistics table for days when nothing was fetched
+  // or precached.
+  for (PrecacheStatisticsTable::PrecacheStatisticsMap::const_iterator it =
+           stats_map.begin();
+       it != stats_map.end(); ++it) {
+    RecordSingleDayPrecacheUMA(it->second);
+  }
+
+  precache_statistics_table_->DeleteOldStats(current_time);
+}
+
+void PrecacheDatabase::RecordURLPrecached(const GURL& url,
+                                          const base::Time& fetch_time,
+                                          int64 size, bool was_cached) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(db_);

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

These are implicit in IsDatabaseAccessible().

[sclittle, 2013/11/19 23:27:10]

Done.

+
+  if (!IsDatabaseAccessible()) {
+    // Don't track anything if unable to access the database.
+    return;
+  }
+
+  if (was_cached && !precache_url_table_->HasURL(url)) {
+    // Since the precache came from the cache, and there's no entry in the URL
+    // table for the URL, this means that the resource was already in the cache
+    // because of user browsing. Thus, this precache had no effect, so ignore
+    // it.
+    return;
+  }
+

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

Probably should start a transaction here.

[sclittle, 2013/11/19 23:27:10]

Done.

+  if (!was_cached) {
+    // The precache only counts as overhead if it was downloaded over the
+    // network.
+    PrecacheStatisticsTable::PrecacheStatistics stats;
+    stats.downloaded_precache_motivated_bytes = size;
+    precache_statistics_table_->IncreaseDailyStats(fetch_time, stats);
+  }
+
+  // Use the URL table to keep track of URLs that are in the cache thanks to
+  // precaching. If a row for the URL already exists, than update the timestamp
+  // to |fetch_time|.
+  precache_url_table_->AddURL(url, fetch_time);
+}
+
+void PrecacheDatabase::RecordURLFetched(const GURL& url,
+                                        const base::Time& fetch_time,
+                                        int64 size, bool was_cached,
+                                        bool is_connection_cellular) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(db_);

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

These are implicit in IsDatabaseAccessible().

[sclittle, 2013/11/19 23:27:10]

Done.

+
+  if (!IsDatabaseAccessible()) {
+    // Don't track anything if unable to access the database.
+    return;
+  }
+

[Scott Hess - ex-Googler, 2013/11/19 18:47:48]

Probably should open a transaction here.

[sclittle, 2013/11/19 23:27:10]

Done.

+  if (was_cached && !precache_url_table_->HasURL(url)) {
+    // Ignore cache hits that precache can't take credit for.
+    return;
+  }
+
+  PrecacheStatisticsTable::PrecacheStatistics stats;
+
+  if (!was_cached) {
+    // The fetch was served over the network during user browsing, so count it
+    // as downloaded non-precache bytes.
+    stats.downloaded_non_precache_bytes = size;
+    if (is_connection_cellular) {
+      stats.downloaded_non_precache_bytes_cellular = size;
+    }
+  } else {
+    // The fetch was served from the cache, and since there's an entry for this
+    // URL in the URL table, this means that the resource was served from the
+    // cache only because precaching put it there. Thus, precaching was helpful,
+    // so count the fetch as saved bytes.
+    stats.saved_bytes = size;
+    if (is_connection_cellular) {
+      stats.saved_bytes_cellular = size;
+    }
+  }
+  precache_statistics_table_->IncreaseDailyStats(fetch_time, stats);
+
+  // Since the resource has been fetched during user browsing, remove any record
+  // of that URL having been precached from the URL table, if any exists.
+  // The current fetch would have put this resource in the cache regardless of
+  // whether or not it was previously precached, so delete any record of that
+  // URL having been precached from the URL table.
+  precache_url_table_->DeleteURL(url);
+}
+
+bool PrecacheDatabase::IsDatabaseAccessible() const {
+  DCHECK(CalledOnValidThread());
+  DCHECK(db_);
+
+  return db_->is_open();
+}
+
+}  // namespace precache