docs(storage): add zonal bucket pre-warmed writer pool sample

Adds storage_optimize_write_latency_pool sample (region tag: storage_optimize_write_latency_pool) demonstrating a pre-warmed pool of AsyncAppendableObjectWriter instances with finalize_on_close=False to avoid object creation and finalization metadata overhead on the critical write path.

Verified with both mock unit tests and live integration testing against a Rapid (zonal) bucket in us-central1-a:

  Running live Python test against bucket=<zonal-bucket>, prefix=live_py_pool_1790087453494
  Python 1. Init pool (3 writers): 862.92 ms
  Python 2. Write+flush: 82.28 ms
  Python 4. Read back: b'0123456789', pool size after refill: 3
  Ran 1 test in 1.612s
  OK

Author: NickGoog

storage/samples/snippets/zonal_buckets/README.md

@@ -75,4 +75,12 @@ This snippet downloads a range of bytes from multiple objects concurrently.
 
 ```bash
 python samples/snippets/zonal_buckets/storage_open_multiple_objects_ranged_read.py --bucket_name <bucket_name> --object_names <object_name_1> <object_name_2>
+```
+
+### Optimize write latency with a pre-warmed writer pool
+
+This snippet uses a pre-warmed pool of writers for a zonal bucket.
+
+```bash
+python samples/snippets/zonal_buckets/storage_optimize_write_latency_pool.py --bucket_name <bucket_name> --key_prefix <key_prefix>
 ```

storage/samples/snippets/zonal_buckets/storage_optimize_write_latency_pool.py

@@ -0,0 +1,134 @@
+#!/usr/bin/env python
+
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import asyncio
+from io import BytesIO
+
+from google.cloud.storage.asyncio.async_appendable_object_writer import (
+    AsyncAppendableObjectWriter,
+)
+from google.cloud.storage.asyncio.async_grpc_client import AsyncGrpcClient
+from google.cloud.storage.asyncio.async_multi_range_downloader import (
+    AsyncMultiRangeDownloader,
+)
+
+
+# [START storage_optimize_write_latency_pool]
+async def storage_optimize_write_latency_pool(
+    bucket_name: str, key_prefix: str, pool_size: int = 3, grpc_client=None
+):
+    """Uses a pre-warmed pool of writers for a zonal bucket.
+
+    grpc_client: an existing grpc_client to use, this is only for testing.
+    """
+    # The ID of your GCS zonal bucket
+    # bucket_name = "your-unique-bucket-name"
+
+    # The prefix for your pooled GCS objects
+    # key_prefix = "pooled-object"
+
+    grpc_client_created = False
+    if grpc_client is None:
+        grpc_client = AsyncGrpcClient()
+        grpc_client_created = True
+
+    next_object_name = f"{key_prefix}_{pool_size}"
+
+    async def new_prewarmed_writer(name: str) -> AsyncAppendableObjectWriter:
+        w = AsyncAppendableObjectWriter(
+            client=grpc_client,
+            bucket_name=bucket_name,
+            object_name=name,
+            generation=0,
+        )
+        await w.open()
+        await w.flush()  # Forces 0-byte object creation in the background.
+        return w
+
+    # 1. Init pool: Flushing incurs operation charges, so size the pool
+    # carefully.
+    pool = list(
+        await asyncio.gather(
+            *(
+                new_prewarmed_writer(f"{key_prefix}_{i}")
+                for i in range(pool_size)
+            )
+        )
+    )
+
+    try:
+        # 2. Write: Pop a pre-warmed writer; append() writes and flushes data
+        # (~1-2 ms).
+        writer = pool.pop(0)
+        await writer.append(b"0123456789")
+
+        # 3. Pool maintenance (run asynchronously off the critical write path):
+        # Close the used writer without finalizing, refill the pool, and
+        # discard stale writers.
+        async def maintain_pool(
+            used: AsyncAppendableObjectWriter, next_name: str
+        ):
+            await used.close(finalize_on_close=False)
+            pool.append(await new_prewarmed_writer(next_name))
+
+        maintenance_task = asyncio.create_task(
+            maintain_pool(writer, next_object_name)
+        )
+
+        # 4. Read: Unfinalized objects are readable after flush().
+        mrd = AsyncMultiRangeDownloader(
+            grpc_client, bucket_name, f"{key_prefix}_0"
+        )
+        await mrd.open()
+        buf = BytesIO()
+        await mrd.download_ranges([(0, 0, buf)])
+        await mrd.close()
+
+        await maintenance_task
+        print(
+            f"Read unfinalized object {key_prefix}_0: "
+            f"{buf.getvalue().decode('utf-8')}"
+        )
+    finally:
+        for rem in pool:
+            await rem.close(finalize_on_close=False)
+        if grpc_client_created:
+            await grpc_client.close()
+
+
+# [END storage_optimize_write_latency_pool]
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(
+        description=__doc__,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+    )
+    parser.add_argument(
+        "--bucket_name", help="Your Cloud Storage zonal bucket name."
+    )
+    parser.add_argument(
+        "--key_prefix", help="Prefix for pooled object names."
+    )
+    args = parser.parse_args()
+
+    asyncio.run(
+        storage_optimize_write_latency_pool(
+            bucket_name=args.bucket_name,
+            key_prefix=args.key_prefix,
+        )
+    )

storage/samples/snippets/zonal_buckets/zonal_snippets_test.py

@@ -1,4 +1,4 @@
-# Copyright 2025 Google, Inc.
+# Copyright 2025 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,17 +13,16 @@
 # limitations under the License.
 
 import asyncio
-import uuid
+import contextlib
 import os
+import uuid
 
-import pytest
 from google.cloud.storage import Client
-import contextlib
-
-from google.cloud.storage.asyncio.async_grpc_client import AsyncGrpcClient
 from google.cloud.storage.asyncio.async_appendable_object_writer import (
     AsyncAppendableObjectWriter,
 )
+from google.cloud.storage.asyncio.async_grpc_client import AsyncGrpcClient
+import pytest
 
 # Import all the snippets
 import storage_create_and_write_appendable_object
@@ -32,6 +31,7 @@
 import storage_open_object_multiple_ranged_read
 import storage_open_object_read_full_object
 import storage_open_object_single_ranged_read
+import storage_optimize_write_latency_pool
 import storage_pause_and_resume_appendable_upload
 import storage_read_appendable_object_tail
 
@@ -258,3 +258,19 @@ def test_storage_open_multiple_objects_ranged_read(
     blob2 = json_client.bucket(_ZONAL_BUCKET).blob(blob2_name)
     blob1.delete()
     blob2.delete()
+
+
+def test_storage_optimize_write_latency_pool(
+    async_grpc_client, json_client, event_loop, capsys
+):
+    key_prefix = f"test-writer-pool-{uuid.uuid4()}"
+    event_loop.run_until_complete(
+        storage_optimize_write_latency_pool.storage_optimize_write_latency_pool(
+            _ZONAL_BUCKET, key_prefix, pool_size=3, grpc_client=async_grpc_client
+        )
+    )
+    out, _ = capsys.readouterr()
+    assert f"Read unfinalized object {key_prefix}_0: 0123456789" in out
+    bucket = json_client.bucket(_ZONAL_BUCKET)
+    for i in range(4):
+        bucket.blob(f"{key_prefix}_{i}").delete()