added JournalStats

Summary: Added JournalStats to start tracking basic stats on the Journal

Reviewed By: chadaustin

Differential Revision: D15565886

fbshipit-source-id: b7345df377303fc442ecf4c112afa7493bb2dc28

eden/fs/journal/Journal.cpp

@@ -87,5 +87,23 @@ bool Journal::isSubscriberValid(uint64_t id) const {
   return subscribers.find(id) != subscribers.end();
 }
 
+std::optional<JournalStats> Journal::getStats() {
+  JournalStats stats;
+  auto curr = getLatest();
+  if (curr == nullptr) {
+    // return None since this is an empty journal
+    return std::nullopt;
+  }
+  stats.latestTimestamp = curr->toTime;
+  stats.earliestTimestamp = curr->fromTime;
+  while (curr != nullptr) {
+    ++stats.entryCount;
+    stats.latestTimestamp = std::max(stats.latestTimestamp, curr->toTime);
+    stats.earliestTimestamp = std::min(stats.earliestTimestamp, curr->fromTime);
+    curr = curr->previous;
+  }
+  return stats;
+}
+
 } // namespace eden
 } // namespace facebook

eden/fs/journal/Journal.h

@@ -11,14 +11,23 @@
 
 #include <folly/Function.h>
 #include <folly/Synchronized.h>
+#include <algorithm>
 #include <cstdint>
 #include <memory>
+#include <optional>
 #include <unordered_map>
 #include "eden/fs/journal/JournalDelta.h"
 
 namespace facebook {
 namespace eden {
 
+/** Contains statistics about the current state of the journal */
+struct JournalStats {
+  uint64_t entryCount = 0;
+  std::chrono::steady_clock::time_point earliestTimestamp;
+  std::chrono::steady_clock::time_point latestTimestamp;
+};
+
 /** The Journal exists to answer questions about how files are changing
  * over time.
  *
@@ -79,6 +88,10 @@ class Journal {
   void cancelAllSubscribers();
   bool isSubscriberValid(SubscriberId id) const;
 
+  /** Returns an option that is nullopt if the Journal is empty or an option
+   * that contains valid JournalStats if the Journal is non-empty*/
+  std::optional<JournalStats> getStats();
+
  private:
   struct DeltaState {
     /** The sequence number that we'll use for the next entry

eden/fs/journal/test/JournalTest.cpp

@@ -171,3 +171,86 @@ TEST(Journal, destruction_does_not_overflow_stack_on_long_chain) {
     journal.addDelta(std::move(delta));
   }
 }
+
+TEST(Journal, empty_journal_returns_none_for_stats) {
+  // Empty journal returns None for stats
+  Journal journal;
+  auto stats = journal.getStats();
+  ASSERT_FALSE(stats.has_value());
+}
+
+TEST(Journal, basic_journal_stats) {
+  Journal journal;
+  // Journal with 1 entry
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::REMOVED));
+  auto from1 = journal.getLatest()->fromTime;
+  auto to1 = journal.getLatest()->toTime;
+  auto stats = journal.getStats();
+  ASSERT_TRUE(stats.has_value());
+  ASSERT_EQ(1, stats->entryCount);
+  ASSERT_EQ(from1, stats->earliestTimestamp);
+  ASSERT_EQ(to1, stats->latestTimestamp);
+
+  // Journal with 2 entries
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::CREATED));
+  stats = journal.getStats();
+  auto to2 = journal.getLatest()->toTime;
+  ASSERT_TRUE(stats.has_value());
+  ASSERT_EQ(2, stats->entryCount);
+  ASSERT_EQ(from1, stats->earliestTimestamp);
+  ASSERT_EQ(to2, stats->latestTimestamp);
+}
+
+TEST(Journal, merge_journal_stats) {
+  Journal journal;
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::REMOVED));
+  auto from1 = journal.getLatest()->fromTime;
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::CREATED));
+  auto stats = journal.getStats();
+  auto to2 = journal.getLatest()->toTime;
+
+  // Journal with 2 entries merged into 1 entry
+  auto latest = journal.getLatest();
+  journal.replaceJournal(latest->merge());
+  stats = journal.getStats();
+  ASSERT_TRUE(stats.has_value());
+  ASSERT_EQ(1, stats->entryCount);
+  ASSERT_EQ(from1, stats->earliestTimestamp);
+  ASSERT_EQ(to2, stats->latestTimestamp);
+}
+
+TEST(Journal, prune_journal_stats) {
+  Journal journal;
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::REMOVED));
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::CREATED));
+  auto stats = journal.getStats();
+  auto from2 = journal.getLatest()->fromTime;
+  auto to2 = journal.getLatest()->toTime;
+  auto latest = journal.getLatest();
+  // Journal with the first entry pruned
+  journal.replaceJournal(latest->merge(2, true));
+  stats = journal.getStats();
+  ASSERT_TRUE(stats.has_value());
+  ASSERT_EQ(1, stats->entryCount);
+  ASSERT_EQ(from2, stats->earliestTimestamp);
+  ASSERT_EQ(to2, stats->latestTimestamp);
+}
+
+TEST(Journal, fully_pruned_journal_stats) {
+  Journal journal;
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::REMOVED));
+  journal.addDelta(std::make_unique<JournalDelta>(
+      "test.txt"_relpath, JournalDelta::CREATED));
+  auto latest = journal.getLatest();
+  // Journal with all entries pruned
+  journal.replaceJournal(latest->merge(3, true));
+  auto stats = journal.getStats();
+  ASSERT_FALSE(stats.has_value());
+}