[8.x] ESQL: supplement docs on LIMIT (#125967) (#126396)

Backport of #125839.

Author: bpintea

docs/reference/esql/esql-limitations.asciidoc

@@ -9,7 +9,7 @@
 [[esql-max-rows]]
 === Result set size limit
 
-By default, an {esql} query returns up to 1000 rows. You can increase the number
+By default, an {esql} query returns up to 1,000 rows. You can increase the number
 of rows up to 10,000 using the <<esql-limit>> command.
 include::processing-commands/limit.asciidoc[tag=limitation]
 

docs/reference/esql/processing-commands/limit.asciidoc

@@ -22,24 +22,54 @@ The maximum number of rows to return.
 The `LIMIT` processing command enables you to limit the number of rows that are
 returned.
 // tag::limitation[]
-Queries do not return more than 10,000 rows, regardless of the `LIMIT` command's
-value.
+For instance,
+```
+FROM index | WHERE field = "value"
+```
+is equivalent to:
+```
+FROM index | WHERE field = "value" | LIMIT 1000
+```
 
-This limit only applies to the number of rows that are retrieved by the query.
-Queries and aggregations run on the full data set.
+Queries do not return more than 10,000 rows, regardless of the `LIMIT` command’s value. This is a configurable upper limit.
 
 To overcome this limitation:
 
-* Reduce the result set size by modifying the query to only return relevant
-data. Use <<esql-where>> to select a smaller subset of the data.
-* Shift any post-query processing to the query itself. You can use the {esql}
-<<esql-stats-by>> command to aggregate data in the query.
+* Reduce the result set size by modifying the query to only return relevant data. Use <<esql-where>> to select a smaller subset of the data.
+* Shift any post-query processing to the query itself. You can use the {esql} <<esql-stats-by>> command to aggregate data in the query.
 
-The default and maximum limits can be changed using these dynamic cluster
-settings:
+The upper limit only applies to the number of rows that are output by the query, not to the number of documents it processes: the query runs on the full data set.
+
+Consider the following two queries:
+```
+FROM index | WHERE field0 == "value" | LIMIT 20000
+```
+and
+```
+FROM index | STATS AVG(field1) BY field2 | LIMIT 20000
+```
+
+In both cases, the filtering by `field0` in the first query or the grouping by `field2` in the second is applied over all the documents present in the `index`, irrespective of their number or indexes size. However, both queries will return at most 10,000 rows, even if there were more rows available to return.
+
+The default and maximum limits can be changed using these dynamic cluster settings:
 
 * `esql.query.result_truncation_default_size`
 * `esql.query.result_truncation_max_size`
+
+However, doing so involves trade-offs. A larger result-set involves a higher memory pressure and increased processing times; the internode traffic within and across clusters can also increase.
+
+These limitations are similar to those enforced by the <<paginate-search-results>>.
+
+[%header.monospaced.styled,format=dsv,separator=|]
+|===
+
+Functionality | Search | {esql}
+Results returned by default | 10 | 1.000
+Default upper limit | 10,000 | 10,000
+Specify number of results | `size` | `LIMIT`
+Change default number of results | n/a | esql.query.result_truncation_default_size
+Change default upper limit | index-max-result-window | esql.query.result_truncation_max_size
+|===
 // end::limitation[]
 
 *Example*