From 282367797723be52edecd42913202926d36b52f6 Mon Sep 17 00:00:00 2001
From: Deepak Cherian <deepak@cherian.net>
Date: Thu, 25 Apr 2024 21:56:24 -0600
Subject: [PATCH] Tweak threshold

---
 flox/core.py | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/flox/core.py b/flox/core.py
index f6d65121..fcecff23 100644
--- a/flox/core.py
+++ b/flox/core.py
@@ -271,8 +271,14 @@ def chunk_unique(labels, slicer, nlabels, label_is_present=None):
         return uniques
 
     # TODO: needs a better heuristic
-    if nlabels < 2 * approx_chunk_size:
-        logger.debug("Using threadpool since %s < 5 * %s", nlabels, approx_chunk_size)
+    THRESHOLD = 2
+    if nlabels < THRESHOLD * approx_chunk_size:
+        logger.debug(
+            "Using threadpool since num_labels %s < %d * chunksize %s",
+            nlabels,
+            THRESHOLD,
+            approx_chunk_size,
+        )
         with ThreadPoolExecutor() as executor:
             futures = [
                 executor.submit(chunk_unique, labels, slicer, nlabels)
@@ -281,6 +287,12 @@ def chunk_unique(labels, slicer, nlabels, label_is_present=None):
             cols = tuple(f.result() for f in futures)
 
     else:
+        logger.debug(
+            "Using serial loop since num_labels %s > %d * chunksize %s",
+            nlabels,
+            THRESHOLD,
+            approx_chunk_size,
+        )
         cols = []
         # Add one to handle the -1 sentinel value
         label_is_present = np.zeros((nlabels + 1,), dtype=bool)