Modernize mongodb docs

plugins/inputs/mongodb/README.md

-# Telegraf plugin: MongoDB
+# MongoDB Input Plugin
 
-#### Configuration
+### Configuration:
 
 ```toml
 [[inputs.mongodb]]
@@ -10,7 +10,9 @@
   ##   mongodb://user:auth_key@10.10.3.30:27017,
   ##   mongodb://10.10.3.33:18832,
   servers = ["mongodb://127.0.0.1:27017"]
-  gather_perdb_stats = false
+
+  ## When true, collect per database stats
+  # gather_perdb_stats = false
 
   ## Optional SSL Config
   # ssl_ca = "/etc/telegraf/ca.pem"
@@ -27,7 +29,58 @@ command the you will get this error on telegraf
 Error in input [mongodb]: not authorized on admin to execute command { serverStatus: 1, recordStats: 0 }
 ```
 
-#### Description
+### Metrics:
+
+- mongodb
+  - tags:
+    - hostname
+  - fields:
+    - active_reads (integer)
+    - active_writes (integer)
+    - commands_per_sec (integer)
+    - deletes_per_sec (integer)
+    - flushes_per_sec (integer)
+    - getmores_per_sec (integer)
+    - inserts_per_sec (integer)
+    - jumbo_chunks (integer)
+    - member_status (string)
+    - net_in_bytes (integer)
+    - net_out_bytes (integer)
+    - open_connections (integer)
+    - percent_cache_dirty (float)
+    - percent_cache_used (float)
+    - queries_per_sec (integer)
+    - queued_reads (integer)
+    - queued_writes (integer)
+    - repl_commands_per_sec (integer)
+    - repl_deletes_per_sec (integer)
+    - repl_getmores_per_sec (integer)
+    - repl_inserts_per_sec (integer)
+    - repl_lag (integer)
+    - repl_queries_per_sec (integer)
+    - repl_updates_per_sec (integer)
+    - resident_megabytes (integer)
+    - state (string)
+    - total_available (integer)
+    - total_created (integer)
+    - total_in_use (integer)
+    - total_refreshing (integer)
+    - ttl_deletes_per_sec (integer)
+    - ttl_passes_per_sec (integer)
+    - updates_per_sec (integer)
+    - vsize_megabytes (integer)
+    - wtcache_app_threads_page_read_count (integer)
+    - wtcache_app_threads_page_read_time (integer)
+    - wtcache_app_threads_page_write_count (integer)
+    - wtcache_bytes_read_into (integer)
+    - wtcache_bytes_written_from (integer)
+    - wtcache_current_bytes (integer)
+    - wtcache_max_bytes_configured (integer)
+    - wtcache_pages_evicted_by_app_thread (integer)
+    - wtcache_pages_queued_for_eviction (integer)
+    - wtcache_server_evicting_pages (integer)
+    - wtcache_tracked_dirty_bytes (integer)
+    - wtcache_worker_thread_evictingpages (integer)
 
 The telegraf plugin collects mongodb stats exposed by serverStatus and few more
 and create a single measurement containing values e.g.
@@ -58,15 +111,24 @@ and create a single measurement containing values e.g.
  * repl_lag
  * repl_oplog_window_s
  * jumbo_chunks (only if mongos or mongo config)
+- mongodb_db_stats
+  - tags:
+    - db_name
+    - hostname
+  - fields:
+    - avg_obj_size (float)
+    - collections (integer)
+    - data_size (integer)
+    - index_size (integer)
+    - indexes (integer)
+    - num_extents (integer)
+    - objects (integer)
+    - ok (integer)
+    - storage_size (integer)
+    - type (string)
 
-If gather_db_stats is set to true, it will also collect per database stats exposed by db.stats()
-creating another measurement called mongodb_db_stats and containing values:
- * collections
- * objects
- * avg_obj_size
- * data_size
- * storage_size
- * num_extents
- * indexes
- * index_size
- * ok
+### Example Output:
+```
+mongodb,hostname=127.0.0.1:27017 active_reads=0i,active_writes=0i,commands_per_sec=6i,deletes_per_sec=0i,flushes_per_sec=0i,getmores_per_sec=1i,inserts_per_sec=0i,jumbo_chunks=0i,member_status="PRI",net_in_bytes=851i,net_out_bytes=23904i,open_connections=6i,percent_cache_dirty=0,percent_cache_used=0,queries_per_sec=2i,queued_reads=0i,queued_writes=0i,repl_commands_per_sec=0i,repl_deletes_per_sec=0i,repl_getmores_per_sec=0i,repl_inserts_per_sec=0i,repl_lag=0i,repl_queries_per_sec=0i,repl_updates_per_sec=0i,resident_megabytes=67i,state="PRIMARY",total_available=0i,total_created=0i,total_in_use=0i,total_refreshing=0i,ttl_deletes_per_sec=0i,ttl_passes_per_sec=0i,updates_per_sec=0i,vsize_megabytes=729i,wtcache_app_threads_page_read_count=4i,wtcache_app_threads_page_read_time=18i,wtcache_app_threads_page_write_count=6i,wtcache_bytes_read_into=10075i,wtcache_bytes_written_from=115711i,wtcache_current_bytes=86038i,wtcache_max_bytes_configured=1073741824i,wtcache_pages_evicted_by_app_thread=0i,wtcache_pages_queued_for_eviction=0i,wtcache_server_evicting_pages=0i,wtcache_tracked_dirty_bytes=0i,wtcache_worker_thread_evictingpages=0i 1522798796000000000
+mongodb_db_stats,db_name=local,hostname=127.0.0.1:27017 avg_obj_size=818.625,collections=5i,data_size=6549i,index_size=86016i,indexes=4i,num_extents=0i,objects=8i,ok=1i,storage_size=118784i,type="db_stat" 1522799074000000000
+```

plugins/inputs/mongodb/mongodb.go

@@ -45,7 +45,9 @@ var sampleConfig = `
   ##   mongodb://user:auth_key@10.10.3.30:27017,
   ##   mongodb://10.10.3.33:18832,
   servers = ["mongodb://127.0.0.1:27017"]
-  gather_perdb_stats = false
+
+  ## When true, collect per database stats
+  # gather_perdb_stats = false
 
   ## Optional SSL Config
   # ssl_ca = "/etc/telegraf/ca.pem"