Database engine (#5282)

* Database engine prototype version 0

* Database engine initial integration with netdata POC

* Scalable database engine with file and memory management.

* Database engine integration with netdata

* Added MIN MAX definitions to fix alpine build of travis CI

* Bugfix for backends and new DB engine, remove useless rrdset_time2slot() calls and erroneous checks

* DB engine disk protocol correction

* Moved DB engine storage file location to /var/cache/netdata/{host}/dbengine

* Fix configure to require openSSL for DB engine

* Fix netdata daemon health not holding read lock when iterating chart dimensions

* Optimized query API for new DB engine and old netdata DB fallback code-path

* netdata database internal query API improvements and cleanup

* Bugfix for DB engine queries returning empty values

* Added netdata internal check for data queries for old and new DB

* Added statistics to DB engine and fixed memory corruption bug

* Added preliminary charts for DB engine statistics

* Changed DB engine ratio statistics to incremental

* Added netdata statistics charts for DB engine internal statistics

* Fix for netdata not compiling successfully when missing dbengine dependencies

* Added DB engine functional test to netdata unittest command parameter

* Implemented DB engine dataset generator based on example.random chart

* Fix build error in CI

* Support older versions of libuv1

* Fixes segmentation fault when using multiple DB engine instances concurrently

* Fix memory corruption bug

* Fixed createdataset advanced option not exiting

* Fix for DB engine not working on FreeBSD

* Support FreeBSD library paths of new dependencies

* Workaround for unsupported O_DIRECT in OS X

* Fix unittest crashing during cleanup

* Disable DB engine FS caching in Apple OS X since O_DIRECT is not available

* Fix segfault when unittest and DB engine dataset generator don't have permissions to create temporary host

* Modified DB engine dataset generator to create multiple files

* Toned down overzealous page cache prefetcher

* Reduce internal memory fragmentation for page-cache data pages

* Added documentation describing the DB engine

* Documentation bugfixes

* Fixed unit tests compilation errors since last rebase

* Added note to back-up the DB engine files in documentation

* Added codacy fix.

* Support old gcc versions for atomic counters in DB engine

1 files changed, 7 insertions, 0 deletions

diff --git a/web/api/formatters/json_wrapper.c b/web/api/formatters/json_wrapper.c
index 2538835680..4911d2f0ea 100644
--- a/web/api/formatters/json_wrapper.c
+++ b/web/api/formatters/json_wrapper.c
@@ -96,12 +96,19 @@ void rrdr_json_wrapper_begin(RRDR *r, BUFFER *wb, uint32_t format, RRDR_OPTIONS
         if(i) buffer_strcat(wb, ", ");
         i++;
 
+        calculated_number value = rd->last_stored_value;
+        if (NAN == value)
+            buffer_strcat(wb, "null");
+        else
+            buffer_rrd_value(wb, value);
+        /*
         storage_number n = rd->values[rrdset_last_slot(r->st)];
 
         if(!does_storage_number_exist(n))
             buffer_strcat(wb, "null");
         else
             buffer_rrd_value(wb, unpack_storage_number(n));
+        */
     }
     if(!i) {
         rows = 0;