From 22824fd83c867cf2c6bd07d4d7124b40771a237f Mon Sep 17 00:00:00 2001
From: Matej Ferencevic <matej.ferencevic@memgraph.io>
Date: Wed, 17 Oct 2018 14:03:54 +0200
Subject: [PATCH] Simplify snapshot and WAL filenames

Reviewers: teon.banek, msantl

Reviewed By: msantl

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1669
---
 src/durability/single_node/paths.cpp | 50 +++++++++++++++-------------
 src/utils/timestamp.hpp              |  8 ++---
 2 files changed, 30 insertions(+), 28 deletions(-)

diff --git a/src/durability/single_node/paths.cpp b/src/durability/single_node/paths.cpp
index 6a85cd40f..122b9c7c5 100644
--- a/src/durability/single_node/paths.cpp
+++ b/src/durability/single_node/paths.cpp
@@ -14,32 +14,34 @@ namespace durability {
 
 namespace fs = std::experimental::filesystem;
 
+// This is the prefix used for WAL and Snapshot filenames. It is a timestamp
+// format that equals to: YYYYmmddHHMMSSffffff
+const std::string kTimestampFormat =
+    "{:04d}{:02d}{:02d}{:02d}{:02d}{:02d}{:06d}";
+
+// TODO: This shouldn't be used to get the transaction ID from a WAL file,
+// instead the file should be parsed and the transaction ID should be read from
+// the file.
 std::experimental::optional<tx::TransactionId> TransactionIdFromWalFilename(
     const std::string &name) {
-  auto nullopt = std::experimental::nullopt;
+  if (utils::EndsWith(name, "current"))
+    return std::numeric_limits<tx::TransactionId>::max();
   // Get the max_transaction_id from the file name that has format
-  // "XXXXX__max_transaction_<MAX_TRANS_ID>"
-  auto file_name_split = utils::RSplit(name, "__", 1);
+  // "XXXXX_tx_<MAX_TRANS_ID>"
+  auto file_name_split = utils::RSplit(name, "_", 1);
   if (file_name_split.size() != 2) {
     LOG(WARNING) << "Unable to parse WAL file name: " << name;
-    return nullopt;
+    return std::experimental::nullopt;
   }
-  if (utils::StartsWith(file_name_split[1], "current"))
-    return std::numeric_limits<tx::TransactionId>::max();
-  file_name_split = utils::Split(file_name_split[1], "_");
-  if (file_name_split.size() != 3) {
-    LOG(WARNING) << "Unable to parse WAL file name: " << name;
-    return nullopt;
-  }
-  auto &tx_id_str = file_name_split[2];
+  auto &tx_id_str = file_name_split[1];
   try {
     return std::stoll(tx_id_str);
   } catch (std::invalid_argument &) {
     LOG(WARNING) << "Unable to parse WAL file name tx ID: " << tx_id_str;
-    return nullopt;
+    return std::experimental::nullopt;
   } catch (std::out_of_range &) {
     LOG(WARNING) << "WAL file name tx ID too large: " << tx_id_str;
-    return nullopt;
+    return std::experimental::nullopt;
   }
 }
 
@@ -49,42 +51,42 @@ std::experimental::optional<tx::TransactionId> TransactionIdFromWalFilename(
 fs::path WalFilenameForTransactionId(
     const std::experimental::filesystem::path &wal_dir,
     std::experimental::optional<tx::TransactionId> tx_id) {
-  auto file_name = utils::Timestamp::Now().ToIso8601();
+  auto file_name = utils::Timestamp::Now().ToString(kTimestampFormat);
   if (tx_id) {
-    file_name += "__max_transaction_" + std::to_string(*tx_id);
+    file_name += "_tx_" + std::to_string(*tx_id);
   } else {
-    file_name += "__current";
+    file_name += "_current";
   }
   return wal_dir / file_name;
 }
 
 fs::path MakeSnapshotPath(const fs::path &durability_dir,
                           tx::TransactionId tx_id) {
-  std::string date_str =
-      utils::Timestamp(utils::Timestamp::Now())
-          .ToString("{:04d}_{:02d}_{:02d}__{:02d}_{:02d}_{:02d}_{:05d}");
+  std::string date_str = utils::Timestamp::Now().ToString(kTimestampFormat);
   auto file_name = date_str + "_tx_" + std::to_string(tx_id);
   return durability_dir / kSnapshotDir / file_name;
 }
 
+// TODO: This shouldn't be used to get the transaction ID from a snapshot file,
+// instead the file should be parsed and the transaction ID should be read from
+// the file.
 std::experimental::optional<tx::TransactionId>
 TransactionIdFromSnapshotFilename(const std::string &name) {
-  auto nullopt = std::experimental::nullopt;
   auto file_name_split = utils::RSplit(name, "_tx_", 1);
   if (file_name_split.size() != 2) {
     LOG(WARNING) << "Unable to parse snapshot file name: " << name;
-    return nullopt;
+    return std::experimental::nullopt;
   }
   try {
     return std::stoll(file_name_split[1]);
   } catch (std::invalid_argument &) {
     LOG(WARNING) << "Unable to parse snapshot file name tx ID: "
                  << file_name_split[1];
-    return nullopt;
+    return std::experimental::nullopt;
   } catch (std::out_of_range &) {
     LOG(WARNING) << "Unable to parse snapshot file name tx ID: "
                  << file_name_split[1];
-    return nullopt;
+    return std::experimental::nullopt;
   }
 }
 }  // namespace durability
diff --git a/src/utils/timestamp.hpp b/src/utils/timestamp.hpp
index 29d0e8666..df42be256 100644
--- a/src/utils/timestamp.hpp
+++ b/src/utils/timestamp.hpp
@@ -58,16 +58,16 @@ class Timestamp : public TotalOrdering<Timestamp> {
 
   long Sec() const { return time.tm_sec; }
 
-  long Subsec() const { return nsec / 10000; }
+  long Usec() const { return nsec / 1000; }
 
   const std::string ToIso8601() const {
     return fmt::format(fiso8601, Year(), Month(), Day(), Hour(), Min(), Sec(),
-                       Subsec());
+                       Usec());
   }
 
   const std::string ToString(const std::string &format = fiso8601) const {
     return fmt::format(format, Year(), Month(), Day(), Hour(), Min(), Sec(),
-                       Subsec());
+                       Usec());
   }
 
   friend std::ostream &operator<<(std::ostream &stream, const Timestamp &ts) {
@@ -93,7 +93,7 @@ class Timestamp : public TotalOrdering<Timestamp> {
   long nsec;
 
   static constexpr auto fiso8601 =
-      "{:04d}-{:02d}-{:02d}T{:02d}:{:02d}:{:02d}.{:05d}Z";
+      "{:04d}-{:02d}-{:02d}T{:02d}:{:02d}:{:02d}.{:06d}Z";
 };
 
 }  // namespace utils