Increase file cache chunk size from 16 KB to 1 MB

To improve performance when connecting to worker instances over high latency network

Author: nathanchrs

cms/db/filecacher.py

@@ -478,8 +478,7 @@ class FileCacher:
     """
 
     # This value is very arbitrary, and in this case we want it to be a
-    # one-size-fits-all, since we use it for many conversions. It has
-    # been chosen arbitrarily based on performance tests on my machine.
+    # one-size-fits-all, since we use it for many conversions.
     # A few consideration on the value it could assume follow:
     # - The page size of large objects is LOBLKSIZE, which is BLCKSZ/4
     #   (BLCKSZ is the block size of the PostgreSQL database, which is
@@ -489,7 +488,8 @@ class FileCacher:
     # - The `io' module defines a DEFAULT_BUFFER_SIZE constant, whose
     #   value is 8192.
     # CHUNK_SIZE should be a multiple of these values.
-    CHUNK_SIZE = 16 * 1024  # 16 KiB
+    # Note that a too-small value can cause issues on high-latency networks.
+    CHUNK_SIZE = 1024 * 1024  # 1 MiB
     backend: FileCacherBackend
 
     def __init__(self, service: "Service | None" = None, path: str | None = None, null: bool = False):

cmstestsuite/unit_tests/server/file_middleware_test.py

@@ -26,17 +26,20 @@
 from werkzeug.wrappers import Response
 from werkzeug.wsgi import responder
 
-from cms.db.filecacher import TombstoneError
+from cms.db.filecacher import FileCacher, TombstoneError
 from cms.server.file_middleware import FileServerMiddleware
 from cmscommon.digest import bytes_digest
 
 
+# Choose a size that is larger than FileCacher.CHUNK_SIZE.
+TESTFILE_LEN = FileCacher.CHUNK_SIZE + 128
+
+
 class TestFileByDigestMiddleware(unittest.TestCase):
 
     def setUp(self):
-        # Choose a size that is larger than FileCacher.CHUNK_SIZE.
         self.content = \
-            bytes(random.getrandbits(8) for _ in range(17 * 1024))
+            bytes(random.getrandbits(8) for _ in range(TESTFILE_LEN))
         self.digest = bytes_digest(self.content)
 
         self.filename = "foobar.pdf"
@@ -51,7 +54,7 @@ def setUp(self):
         self.provide_filename = True
 
         self.wsgi_app = \
-            FileServerMiddleware(self.file_cacher,self.wrapped_wsgi_app)
+            FileServerMiddleware(self.file_cacher, self.wrapped_wsgi_app)
         self.environ_builder = EnvironBuilder("/some/url")
         self.client = Client(self.wsgi_app, Response)
 
@@ -141,7 +144,7 @@ def test_range_request(self):
         self.assertEqual(response.content_range.units, "bytes")
         self.assertEqual(response.content_range.start, 256)
         self.assertEqual(response.content_range.stop, 768)
-        self.assertEqual(response.content_range.length, 17 * 1024)
+        self.assertEqual(response.content_range.length, TESTFILE_LEN)
         self.assertEqual(response.get_data(), self.content[256:768])
 
     def test_range_request_end_overflows(self):
@@ -151,12 +154,13 @@ def test_range_request_end_overflows(self):
         self.assertEqual(response.content_range.units, "bytes")
         self.assertEqual(response.content_range.start, 256)
         self.assertEqual(response.content_range.stop, 2048)
-        self.assertEqual(response.content_range.length, 17 * 1024)
+        self.assertEqual(response.content_range.length, TESTFILE_LEN)
         self.assertEqual(response.get_data(), self.content[256:2048])
 
     def test_range_request_start_overflows(self):
         # Test a range that starts after the end of the file.
-        response = self.request(headers=[("Range", f"bytes={len(self.content) + 1}-")])
+        response = self.request(
+            headers=[("Range", f"bytes={len(self.content) + 1}-")])
         self.assertEqual(response.status_code, 416)