Feature/turn on unique log ids (#8572)

* turn on unique log message IDs by default

* add missing feature documentation

* update CHANGELOG

CHANGELOG

@@ -3,12 +3,12 @@ devel
 
 * added "--log.ids" option to arangod
 
-  The default value for this option is `false`. Setting the option to `true`
+  The default value for this option is `true`. Setting the option to `false`
-  will embed unique ids into all log messages generated in arangod code. This
+  will prevent embedding unique log ids into all log messages generated by
-  allows for easy access to the location in the source code from which the
+  ArangoDB C++ code. The unique ids allow for easy access to the location in
-  message originates. This should help customers to configure custom
+  the source code from which a message originates. This should help customers
-  monitoring/alerting based on specific log id occurrences and will also be
+  to configure custom monitoring/alerting based on specific log id occurrences
-  helpful for support and development in identifying problems.
+  and will also be helpful for support and development in identifying problems.
 
 * fixed issue #8294: wrong equals behaviour on arrays with ArangoSearch
 

Documentation/Books/Manual/ReleaseNotes/NewFeatures35.md

@@ -20,6 +20,13 @@ reduce memory usage and, for some queries, also execution time for the sorting.
 If the optimization is applied, it will show as "sort-limit" rule in the query execution
 plan.
 
+### Index Hints in AQL
+
+Users may now take advantage of the `indexHint` inline query option to override
+the internal optimizer decision regarding which index to use to serve content
+from a given collection. The index hint works with the named indices feature
+above, making it easy to specify which index to use.
+
 ### Sorted primary index (RocksDB engine)
 
 The query optimizer can now make use of the sortedness of primary indexes if the
@@ -280,12 +287,37 @@ name _cannot_ be changed after index creation. No two indices on the same
 collection may share the same name, but two indices on different collections 
 may.
 
-### Index Hints in AQL
+### ID values in log messages
+
+By default, ArangoDB and its client tools now show a 5 digit unique ID value in
+any of their log messages, e.g.
+
+    2019-03-25T21:23:19Z [8144] INFO [cf3f4] ArangoDB (version 3.5.0 enterprise [linux]) is ready for business. Have fun!.
+
+In this message, the `cf3f4` is the message's unique ID value. ArangoDB users can
+use this ID to build custom monitoring or alerting based on specific log ID values.
+Existing log ID values are supposed to stay constant in future releases of arangod.
+
+Additionally the unique log ID values can be used by the ArangoDB support to find
+out which component of the product exactly generated a log message. The IDs also
+make disambiguation of identical log messages easier.
+
+The presence of these ID values in log messages may confuse custom log message filtering 
+or routing mechanisms that parse log messages and that rely on the old log message
+format.
+
+This can be fixed adjusting any existing log message parsers and making them aware
+of the ID values. The ID values are always 5 byte strings, consisting of the characters
+`[0-9a-f]`. ID values are placed directly behind the log level (e.g. `INFO`) for
+general log messages that do not contain a log topic, and directly behind the log
+topic for messages that contain a topic, e.g. 
+
+    2019-03-25T21:23:19Z [8144] INFO [cf3f4] ArangoDB (version 3.5.0 enterprise [linux]) is ready for business. Have fun!.
+    2019-03-25T21:23:16Z [8144] INFO {authentication} [3844e] Authentication is turned on (system only), authentication for unix sockets is turned on
+
+Alternatively, the log IDs can be suppressed in all log messages by setting the startup
+option `--log.ids false` when starting arangod or any of the client tools.
 
-Users may now take advantage of the `indexHint` inline query option to override
-the internal optimizer decision regarding which index to use to serve content
-from a given collection. The index hint works with the named indices feature
-above, making it easy to specify which index to use.
 
 Internal
 --------

Documentation/Books/Manual/ReleaseNotes/UpgradingChanges35.md

@@ -6,6 +6,34 @@ upgrading to ArangoDB 3.5, and adjust any client programs if necessary.
 
 The following incompatible changes have been made in ArangoDB 3.5:
 
+ID values in log messages
+-------------------------
+
+By default, ArangoDB and its client tools now show a 5 digit unique ID value in
+any of their log messages, e.g.
+
+    2019-03-25T21:23:19Z [8144] INFO [cf3f4] ArangoDB (version 3.5.0 enterprise [linux]) is ready for business. Have fun!.
+
+In this message, the `cf3f4` is the message's unique ID value. ArangoDB users can
+use this ID to build custom monitoring or alerting based on specific log ID values.
+
+The presence of these ID values in log messages may confuse custom log message filtering 
+or routing mechanisms that parse log messages and that rely on the old log message
+format.
+
+This can be fixed adjusting any existing log message parsers and making them aware
+of the ID values. The ID values are always 5 byte strings, consisting of the characters
+`[0-9a-f]`. ID values are placed directly behind the log level (e.g. `INFO`) for
+general log messages that do not contain a log topic, and directly behind the log
+topic for messages that contain a topic, e.g. 
+
+    2019-03-25T21:23:19Z [8144] INFO [cf3f4] ArangoDB (version 3.5.0 enterprise [linux]) is ready for business. Have fun!.
+    2019-03-25T21:23:16Z [8144] INFO {authentication} [3844e] Authentication is turned on (system only), authentication for unix sockets is turned on
+
+Alternatively, the log IDs can be suppressed in all log messages by setting the startup
+option `--log.ids false` when starting arangod or any of the client tools.
+
+
 Startup options
 ---------------
 

lib/Logger/LoggerFeature.cpp

@@ -89,7 +89,9 @@ void LoggerFeature::collectOptions(std::shared_ptr<ProgramOptions> options) {
   options->addOption("--log.use-microtime", "use microtime instead",
                      new BooleanParameter(&_useMicrotime));
 
-  options->addOption("--log.ids", "log unique message ids", new BooleanParameter(&_showIds));
+  options->addOption("--log.ids", "log unique message ids", 
+                     new BooleanParameter(&_showIds))
+                     .setIntroducedIn(30500);
 
   options->addOption("--log.role", "log server role", new BooleanParameter(&_showRole));
 

lib/Logger/LoggerFeature.h

@@ -62,7 +62,7 @@ class LoggerFeature final : public application_features::ApplicationFeature {
   bool _foregroundTty = false;
   bool _forceDirect = false;
   bool _useMicrotime = false;
-  bool _showIds = false;
+  bool _showIds = true;
   bool _showRole = false;
   bool _logRequestParameters = true;
   bool _supervisor = false;