[DOC] Restructure and expand best practices doc (#55)

* Increase the default number of threads to 16

Increase the default number of threads passed to the EventProcessorHost
to 16, to match the standard default.

Re-work docs to reflect the fact the change to defaults, and the fact
that event_hubs*partitions is not the maximum number of threads, and
more threads may yield better performance.

* Restructure best practices docs

* Remove rb file from pr

Co-authored-by: Rob Bavey <[email protected]>

docs/index.asciidoc

@@ -78,35 +78,57 @@ https://portal.azure.com[Azure Portal]`-> Blob Storage account -> Access keys`.
 Here are some guidelines to help you avoid data conflicts that can cause lost
 events.
 
-* **Create a Logstash consumer group.** 
+* <<plugins-{type}s-{plugin}-bp-group>>
+* <<plugins-{type}s-{plugin}-bp-multihub>> 
+* <<plugins-{type}s-{plugin}-bp-threads>> 
+
+[id="plugins-{type}s-{plugin}-bp-group"]
+====== Create a Logstash consumer group
 Create a new consumer group specifically for Logstash. Do not use the $default or
 any other consumer group that might already be in use. Reusing consumer groups
 among non-related consumers can cause unexpected behavior and possibly lost
 events. All Logstash instances should use the same consumer group so that they can
 work together for processing events.
-* **Avoid overwriting offset with multiple Event Hubs.** 
+
+[id="plugins-{type}s-{plugin}-bp-multihub"]
+====== Avoid overwriting offset with multiple Event Hubs
 The offsets (position) of the Event Hubs are stored in the configured Azure Blob
 store. The Azure Blob store uses paths like a file system to store the offsets.
 If the paths between multiple Event Hubs overlap, then the offsets may be stored
 incorrectly. 
+
 To avoid duplicate file paths, use the advanced configuration model and make
 sure that at least one of these options is different per Event Hub:
+
 ** storage_connection
 ** storage_container (defaults to Event Hub name if not defined)
 ** consumer_group
-* **Set number of threads correctly.** 
-The number of threads should equal the number of Event Hubs plus one (or more).
-Each Event Hub needs at least one thread. An additional thread is needed to help
-coordinate the other threads. The number of threads should not exceed the number
-of Event Hubs multiplied by the number of partitions per Event Hub plus one.
-Threads are currently available only as a global setting.  If you are using multiple 
-pipelines, the threads setting applies to each pipeline independently.  
-** Sample scenario: Event Hubs = 4. Partitions on each Event Hub = 3.
-Minimum threads is 5 (4 Event Hubs plus one). Maximum threads is 13 (4 Event
-Hubs times 3 partitions plus one). 
-** If you’re collecting activity logs from one event hub instance, 
+
+
+[id="plugins-{type}s-{plugin}-bp-threads"]
+====== Set number of threads correctly
+
+By default, the number of threads used to service all event hubs is `16`. And while this
+may be sufficient for most use cases, throughput may be improved by refining this number.
+When servicing a large number of partitions across one or more event hubs, setting a higher
+value may result in improved performance. The maximum number of threads is not strictly bound
+by the total number of partitions being serviced, but setting the value much higher than
+that may mean that some threads are idle.
+
+NOTE: The number of threads *must* be greater than or equal to the number of Event hubs plus one.
+
+NOTE: Threads are currently available only as a global setting across all event hubs in a single `azure_event_hubs`
+input definition. However if your configuration includes multiple `azure_event_hubs` inputs, the threads setting applies
+independently to each.
+
+**Sample scenarios** 
+
+* Event Hubs = 4. Partitions on each Event Hub = 3.
+Minimum threads is 5 (4 Event Hubs plus one).
+* If you’re collecting activity logs from one event hub instance, 
 then only 2 threads (1 Event Hub plus one) are required.
 
+
 [id="plugins-{type}s-{plugin}-eh_config_models"]
 ==== Configuration models
 
@@ -478,16 +500,16 @@ azure_event_hubs {
 ===== `threads`
 * Value type is <<number,number>>
 * Minimum value is `2`
-* Default value is `4`
-  
+* Default value is `16`
+
 Total number of threads used to process events. The value you set here applies
 to all Event Hubs. Even with advanced configuration, this value is a global
 setting, and can't be set per event hub. 
 
 [source,ruby]
 ----
 azure_event_hubs {
-   threads => 4
+   threads => 16
 }
 ----