Replace hardcoded pool worker limit with configurable default.

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/config/mod.rs

@@ -2003,6 +2003,20 @@ pub struct Config {
 	#[serde(default = "default_db_pool_workers_limit")]
 	pub db_pool_workers_limit: usize,
 
+	/// Limits the total number of workers across all worker groups. When the
+	/// sum of all groups exceeds this value the worker counts are reduced until
+	/// this constraint is satisfied.
+	///
+	/// By default this value is only effective on larger systems (e.g. 16+
+	/// cores) where it will tamper the overall thread-count. The thread-pool
+	/// model will never achieve hardware capacity but this value can be raised
+	/// on huge systems if the scheduling overhead is determined to not
+	/// bottleneck and the worker groups are divided too small.
+	///
+	/// default: 2048
+	#[serde(default = "default_db_pool_max_workers")]
+	pub db_pool_max_workers: usize,
+
 	/// Determines the size of the queues feeding the database's frontend-pool.
 	/// The size of the queue is determined by multiplying this value with the
 	/// number of pool workers. When this queue is full, tokio tasks conducting
@@ -3149,6 +3163,8 @@ fn default_db_pool_workers() -> usize {
 
 fn default_db_pool_workers_limit() -> usize { 64 }
 
+fn default_db_pool_max_workers() -> usize { 2048 }
+
 fn default_db_pool_queue_mult() -> usize { 4 }
 
 fn default_stream_width_default() -> usize { 32 }

src/database/pool.rs

@@ -65,8 +65,8 @@ pub(crate) type BatchQuery<'a> = SmallVec<[KeyBuf; BATCH_INLINE]>;
 pub(crate) type BatchResult<'a> = SmallVec<[ResultHandle<'a>; BATCH_INLINE]>;
 pub(crate) type ResultHandle<'a> = Result<Handle<'a>>;
 
-const WORKER_LIMIT: (usize, usize) = (1, 1024);
-const QUEUE_LIMIT: (usize, usize) = (1, 4096);
+const WORKER_LIMIT: (usize, usize) = (1, 4096);
+const QUEUE_LIMIT: (usize, usize) = (1, 1024);
 const BATCH_INLINE: usize = 1;
 
 const WORKER_STACK_SIZE: usize = 1_048_576;

src/database/pool/configure.rs

@@ -124,6 +124,7 @@ pub(super) fn configure(server: &Arc<Server>) -> (Vec<usize>, Vec<usize>, Vec<us
 		.filter_map(|mq| mq.nr_tags)
 		.chain(default_worker_count.into_iter())
 		.fold(0_usize, usize::saturating_add)
+		.min(config.db_pool_max_workers)
 		.clamp(WORKER_LIMIT.0, WORKER_LIMIT.1);
 
 	// Tamper for the total number of workers by reducing the count for each group.