Add missing max_file_descriptors option to split cache configuration

Author: earlbread

docs/configuration/node-config.md

@@ -201,7 +201,7 @@ This section contains the configuration options for a Searcher.
 | `fast_field_cache_capacity` | Fast field in memory cache capacity on a Searcher. If your filter by dates, run aggregations, range queries, or even for tracing, it might worth increasing this parameter. The [metrics](../reference/metrics.md) starting by `quickwit_cache_fastfields_cache` can help you make an informed choice when setting this value. | `1G` |
 | `split_footer_cache_capacity` | Split footer in memory cache (it is essentially the hotcache) capacity on a Searcher.| `500M` |
 | `partial_request_cache_capacity` | Partial request in memory cache capacity on a Searcher. Cache intermediate state for a request, possibly making subsequent requests faster. It can be disabled by setting the size to `0`. | `64M` |
-| `max_num_concurrent_split_searches` | Maximum number of concurrent split search requests running on a Searcher. | `100` |
+| `max_num_concurrent_split_searches` | Maximum number of concurrent split search requests running on a Searcher. When `split_cache` is enabled, this value must be less than or equal to `split_cache.max_file_descriptors`. | `100` |
 | `split_cache` | Searcher split cache configuration options defined in the section below. Cache disabled if unspecified. | |
 | `request_timeout_secs` | The time before a search request is cancelled. This should match the timeout of the stack calling into quickwit if there is one set.  | `30` |
 
@@ -214,6 +214,7 @@ This section contains the configuration options for the on-disk searcher split c
 | `max_num_bytes` | Maximum disk size in bytes allowed in the split cache. Can be exceeded by the size of one split. | |
 | `max_num_splits` | Maximum number of splits allowed in the split cache.   | `10000` |
 | `num_concurrent_downloads` | Maximum number of concurrent download of splits. | `1` |
+| `max_file_descriptors` | Maximum number of file descriptors that can be open concurrently for cached splits. This value must be greater than or equal to `max_num_concurrent_split_searches`. | `100` |
 
 
 Example:
@@ -227,6 +228,7 @@ searcher:
     max_num_bytes: 1G
     max_num_splits: 10000
     num_concurrent_downloads: 1
+    max_file_descriptors: 100
 ```
 
 ## Jaeger configuration