temporarily speed up presubmit feedback

Author: parthea

.github/workflows/unittest.yml

@@ -29,7 +29,7 @@ jobs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
       is_full_run: ${{ steps.check-label.outputs.is_full_run }}
     env:
-      MAX_SHARDS: 16
+      MAX_SHARDS: 50
       # Define weights for long-running unit tests to balance shard execution time
       # Each weight is roughly 1 minute of expected execution time
       # Default for unset packages is 1
@@ -113,8 +113,7 @@ jobs:
     - name: Run unit tests
       run: |
         uv pip install --system nox nox-uv
-    # Caches compiled wheels locally to prevent building heavy libraries
-    # such as grpcio, which we build from scratch on every run for Python 3.15+.
+    # Caches local wheels for Python 3.15+ to avoid repeatedly downloading or building heavy libraries.
     # Follow https://github.com/grpc/grpc/issues/41010 for updates.
     - name: Cache Built Python 3.15 Wheels
       if: matrix.python == '3.15'
@@ -124,15 +123,20 @@ jobs:
         key: ${{ runner.os }}-uv-wheels-3.15-${{ hashFiles('packages/**/testing/constraints*.txt') }}
         restore-keys: |
           ${{ runner.os }}-uv-wheels-3.15-
-    # Pre-cache heavy dependencies sequentially before running parallel tests
-    - name: Pre-cache heavy dependencies (grpcio)
+    # TODO: Remove this step once official Python 3.15 wheels for grpcio are published to PyPI.
+    # See https://github.com/grpc/grpc/issues/41010#issuecomment-4848264910 for details.
+    - name: Install grpcio wheel for Python 3.15
       if: matrix.python == '3.15'
       run: |
-        # Create the directory so uv doesn't crash if there is a `cache miss`
         mkdir -p .uv-wheel-cache
-        # Download and compile grpcio sequentially so that parallel test workers
-        # immediately hit the warm cache instead of deadlocking on compilation.
-        uv pip install --system grpcio --find-links .uv-wheel-cache
+        WHEEL_FILE=".uv-wheel-cache/grpcio-1.83.0.dev0-cp315-cp315-manylinux2014_x86_64.manylinux_2_17_x86_64.whl"
+        if [ ! -f "$WHEEL_FILE" ]; then
+          curl -L "https://packages.grpc.io/archive/2026/06/5ccdab32010f762634e1082d19be53cf60458456-b37e49c7-5e62-4cbe-870a-c599bb907b04/python/grpcio/grpcio-1.83.0.dev0-cp315-cp315-manylinux2014_x86_64.manylinux_2_17_x86_64.whl" -o "$WHEEL_FILE"
+        fi
+        echo "d7706633cd5d97a8b8d3c6ed36c5940722a9b5cbb47f0d10bc433ee27af36ff0  $WHEEL_FILE" | sha256sum -c
+        uv pip install --system "$WHEEL_FILE"
+        echo "UV_FIND_LINKS=${{ github.workspace }}/.uv-wheel-cache" >> $GITHUB_ENV
+        echo "UV_CACHE_DIR=${{ github.workspace }}/.uv-wheel-cache" >> $GITHUB_ENV
     - name: Run unit tests for ${{ matrix.package_shard.description }}
       env:
         BUILD_TYPE: presubmit

ci/get_package_shards.py

@@ -165,7 +165,7 @@ def group_packages(packages_map):
 
     # Dynamically determine target weight to balance across max shards.
     max_shards = int(os.environ.get("MAX_SHARDS", 16))
-    target_weight = max(10, math.ceil(total_weight / max_shards))
+    target_weight = max(5, math.ceil(total_weight / max_shards))
 
     shards_list = []
     current_shard_items = []