From 13ff0e9f2aad16682fe188bd8d7c60e6d80a2cf2 Mon Sep 17 00:00:00 2001
From: nameexhaustion <simonlin.rqmmw@slmail.me>
Date: Mon, 12 Aug 2024 21:37:47 +1000
Subject: [PATCH] perf: Reduce default async thread count (#18142)

---
 crates/polars-io/src/pl_async.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/crates/polars-io/src/pl_async.rs b/crates/polars-io/src/pl_async.rs
index b9731751483d..cc43a908cda3 100644
--- a/crates/polars-io/src/pl_async.rs
+++ b/crates/polars-io/src/pl_async.rs
@@ -237,8 +237,16 @@ pub struct RuntimeManager {
 
 impl RuntimeManager {
     fn new() -> Self {
+        let n_threads = std::env::var("POLARS_ASYNC_THREAD_COUNT")
+            .map(|x| x.parse::<usize>().expect("integer"))
+            .unwrap_or((POOL.current_num_threads() / 4).clamp(1, 4));
+
+        if polars_core::config::verbose() {
+            eprintln!("Async thread count: {}", n_threads);
+        }
+
         let rt = Builder::new_multi_thread()
-            .worker_threads(std::cmp::max(POOL.current_num_threads(), 4))
+            .worker_threads(n_threads)
             .enable_io()
             .enable_time()
             .build()