HSEARCH-3879 Clarify the indexing queue settings

documentation/src/main/asciidoc/backend-elasticsearch.asciidoc

@@ -799,20 +799,25 @@ hibernate.search.backends.<backend name>.index_defaults.indexing.max_bulk_size 1
 * `indexing.queue_count` defines the number of queues.
 Expects a strictly positive integer value.
 +
-Higher values may lead to higher indexing throughput,
-but incur a risk of <<backend-elasticsearch-indexing-queues-circuit-breaker,overloading Elasticsearch>>.
+Higher values will lead to more connections being used in parallel,
+which may lead to higher indexing throughput,
+but incurs a risk of <<backend-elasticsearch-indexing-queues-circuit-breaker,overloading Elasticsearch>>,
+leading to Elasticsearch giving up on some requests and resulting in indexing failures.
 * `indexing.queue_size` defines the maximum number of elements each queue can hold.
 Expects a strictly positive integer value.
 +
 Lower values may lead to lower memory usage, especially if there are many queues,
 but values that are too low will reduce the likeliness of reaching the max bulk size
-and increase the likeliness of <<backend-elasticsearch-indexing-queues-blocking,application threads blocking>>,
-potentially leading to lower indexing throughput.
+and increase the likeliness of <<backend-elasticsearch-indexing-queues-blocking,application threads blocking>>
+because the queue is full,
+which may lead to lower indexing throughput.
 * `indexing.max_bulk_size` defines the maximum number of indexing requests in each bulk request.
 Expects a strictly positive integer value.
 +
-Higher values may lead to higher indexing throughput,
-but incur a risk of <<backend-elasticsearch-indexing-queues-circuit-breaker,overloading Elasticsearch>>.
+Higher values will lead to more documents being sent in each HTTP request sent to Elasticsearch,
+which may lead to higher indexing throughput,
+but incurs a risk of <<backend-elasticsearch-indexing-queues-circuit-breaker,overloading Elasticsearch>>,
+leading to Elasticsearch giving up on some requests and resulting in indexing failures.
 +
 Note that raising this number above the queue size has no effect,
 as bulks cannot include more requests than are contained in the queue.

documentation/src/main/asciidoc/backend-lucene.asciidoc

@@ -603,7 +603,8 @@ hibernate.search.backends.<backend name>.index_defaults.indexing.queue_size 1000
 * `indexing.queue_count` defines the number of queues.
 Expects a strictly positive integer value.
 +
-Higher values may lead to higher indexing throughput if CPU is the bottleneck when indexing.
+Higher values will lead to more indexing operations being performed in parallel,
+which may lead to higher indexing throughput if CPU power is the bottleneck when indexing.
 +
 Note that raising this number above the <<backend-lucene-threads,number of threads>> is never useful,
 as the number of threads limits how many queues can be processed in parallel.
@@ -613,6 +614,8 @@ Expects a strictly positive integer value.
 Lower values may lead to lower memory usage, especially if there are many queues,
 but values that are too low will increase the likeliness of
 <<backend-lucene-indexing-queues-blocking,application threads blocking>>
+because the queue is full,
+which may lead to lower indexing throughput.
 
 [TIP]
 [[backend-lucene-indexing-queues-blocking]]