From 2c4accdf342dc2b49b4e293cccb9025a003b1e7c Mon Sep 17 00:00:00 2001
From: Jan <jsteemann@users.noreply.github.com>
Date: Tue, 19 Mar 2019 12:47:57 +0100
Subject: [PATCH] micro improvements for rocksdb options (#8433)

---
 CHANGELOG                                              |  9 +++++++++
 .../Books/Manual/ReleaseNotes/UpgradingChanges35.md    |  6 ++++++
 arangod/RocksDBEngine/RocksDBEngine.cpp                | 10 +++++++++-
 lib/ApplicationFeatures/ApplicationServer.h            |  3 +++
 lib/ApplicationFeatures/RocksDBOptionFeature.cpp       |  3 ++-
 5 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 24ac5b5da1..5a476a57ee 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,15 @@
 devel
 -----
 
+* renamed hidden startup option `--rocksdb.delayed_write_rate` to the more
+  consistent `--rocksdb.delayed-write-rate`. When the old option name is
+  used, the arangod startup will be aborted with a descriptive error message.
+
+* if not explicitly configured, make agency nodes start removing their unused 
+  WAL files a few seconds after the completed server startup already. This is
+  because on agency nodes, unused WAL files do not need to be retained for
+  potential replication clients to read them. 
+
 * added option `--all-databases` to arangodump and arangorestore
 
   When set to true, this makes arangodump dump all available databases
diff --git a/Documentation/Books/Manual/ReleaseNotes/UpgradingChanges35.md b/Documentation/Books/Manual/ReleaseNotes/UpgradingChanges35.md
index 5628e385e3..c0f6b8e915 100644
--- a/Documentation/Books/Manual/ReleaseNotes/UpgradingChanges35.md
+++ b/Documentation/Books/Manual/ReleaseNotes/UpgradingChanges35.md
@@ -6,6 +6,12 @@ upgrading to ArangoDB 3.5, and adjust any client programs if necessary.
 
 The following incompatible changes have been made in ArangoDB 3.5:
 
+Startup options
+---------------
+
+The hidden startup option `--rocksdb.delayed_write_rate` was renamed to the more
+consistent `--rocksdb.delayed-write-rate`. When the old option name is used, the 
+arangod startup will be aborted with a descriptive error message.
 
 Web interface
 -------------
diff --git a/arangod/RocksDBEngine/RocksDBEngine.cpp b/arangod/RocksDBEngine/RocksDBEngine.cpp
index 1c8972e6b1..35a82d3191 100644
--- a/arangod/RocksDBEngine/RocksDBEngine.cpp
+++ b/arangod/RocksDBEngine/RocksDBEngine.cpp
@@ -22,6 +22,7 @@
 /// @author Jan Christoph Uhde
 ////////////////////////////////////////////////////////////////////////////////
 
+#include "ApplicationFeatures/ApplicationServer.h"
 #include "ApplicationFeatures/RocksDBOptionFeature.h"
 #include "Basics/Exceptions.h"
 #include "Basics/FileUtils.h"
@@ -356,6 +357,13 @@ void RocksDBEngine::start() {
   if (!isEnabled()) {
     return;
   }
+  
+  if (ServerState::instance()->isAgent() &&
+      !application_features::ApplicationServer::server->options()->processingResult().touched("rocksdb.wal-file-timeout-initial")) {
+    // reduce --rocksb.wal-file-timeout-initial to 15 seconds for agency nodes
+    // as we probably won't need the WAL for WAL tailing and replication here
+    _pruneWaitTimeInitial = 15; 
+  }
 
   LOG_TOPIC(TRACE, arangodb::Logger::ENGINES)
       << "rocksdb version " << rest::Version::getRocksDBVersion()
@@ -2328,4 +2336,4 @@ void RocksDBEngine::releaseTick(TRI_voc_tick_t tick) {
 
 // -----------------------------------------------------------------------------
 // --SECTION--                                                       END-OF-FILE
-// -----------------------------------------------------------------------------
\ No newline at end of file
+// -----------------------------------------------------------------------------
diff --git a/lib/ApplicationFeatures/ApplicationServer.h b/lib/ApplicationFeatures/ApplicationServer.h
index c154bc4d11..ea61123b3c 100644
--- a/lib/ApplicationFeatures/ApplicationServer.h
+++ b/lib/ApplicationFeatures/ApplicationServer.h
@@ -230,6 +230,9 @@ class ApplicationServer {
 
   // return VPack options
   VPackBuilder options(std::unordered_set<std::string> const& excludes) const;
+  
+  // return the program options object
+  std::shared_ptr<options::ProgramOptions> options() const { return _options; }
 
   // return the server state
   ServerState state() const { return _state; }
diff --git a/lib/ApplicationFeatures/RocksDBOptionFeature.cpp b/lib/ApplicationFeatures/RocksDBOptionFeature.cpp
index e9a7a1efb2..b5a69a10fc 100644
--- a/lib/ApplicationFeatures/RocksDBOptionFeature.cpp
+++ b/lib/ApplicationFeatures/RocksDBOptionFeature.cpp
@@ -153,13 +153,14 @@ void RocksDBOptionFeature::collectOptions(std::shared_ptr<ProgramOptions> option
                      new UInt64Parameter(&_maxTotalWalSize));
 
   options->addOption(
-      "--rocksdb.delayed_write_rate",
+      "--rocksdb.delayed-write-rate",
       "limited write rate to DB (in bytes per second) if we are writing to the "
       "last mem-table allowed and we allow more than 3 mem-tables, or if we "
       "have surpassed a certain number of level-0 files and need to slowdown "
       "writes",
       new UInt64Parameter(&_delayedWriteRate),
       arangodb::options::makeFlags(arangodb::options::Flags::Hidden));
+  options->addOldOption("rocksdb.delayed_write_rate", "rocksdb.delayed-write-rate");
 
   options->addOption("--rocksdb.min-write-buffer-number-to-merge",
                      "minimum number of write buffers that will be merged "