stream-clone: avoid opening a revlog in case we do not need it Opening an revlog has a cost, especially if it is inline as we have to scan the file and construct an index. To prevent the associated slowdown, we just do a minimal scan to check that an inline file is still inline, and simply stream the file without creating a revlog when we can. This provides a big boost compared to the previous changeset, even if the full generation is still penalized by the initial gathering of information. All benchmarks are run on linux with Python 3.10.7. # benchmark.name = hg.exchange.stream.generate # benchmark.variants.version = v2 ### Compared to the previous changesets We get a large win all across the board! # mercurial-2018-08-01-zstd-sparse-revlog before: 0.250694 seconds after: 0.105986 seconds (-57.72%) # pypy-2018-08-01-zstd-sparse-revlog before: 3.885657 seconds after: 1.709748 seconds (-56.00%) # netbeans-2018-08-01-zstd-sparse-revlog before: 16.679371 seconds after: 7.687469 seconds (-53.91%) # mozilla-central-2018-08-01-zstd-sparse-revlog before: 38.575482 seconds after: 17.520316 seconds (-54.58%) # mozilla-try-2019-02-18-zstd-sparse-revlog before: 81.160994 seconds after: 37.073753 seconds (-54.32%) ### Compared to 6.4.3 We are still significantly slower than 6.4.3, the extra time is usually twice slower than the extra time we observe on the locked section, which is a quite interesting information. Except for mercurial-central that is much faster. That discrepancy is not really explained yet. # mercurial-2018-08-01-zstd-sparse-revlog 6.4.3: 0.072560 seconds after: 0.105986 seconds (+46.07%) (- 0.03 seconds) # pypy-2018-08-01-zstd-sparse-revlog 6.4.3: 1.211193 seconds after: 1.709748 seconds (+41.16%) (-0.45 seconds) # netbeans-2018-08-01-zstd-sparse-revlog 6.4.3: 4.932843 seconds after: 7.687469 seconds (+55.84%) (-2.75 seconds) # mozilla-central-2018-08-01-zstd-sparse-revlog 6.4.3: 34.012226 seconds after: 17.520316 seconds (-48.49%) (-16.49 seconds) # mozilla-try-2019-02-18-zstd-sparse-revlog 6.4.3: 23.850555 seconds after: 37.073753 seconds (+55.44%) (+13.22 seconds)

--- a/mercurial/revlog.py	Tue May 30 17:43:59 2023 +0100
+++ b/mercurial/revlog.py	Wed May 31 10:37:55 2023 +0100
@@ -290,6 +290,16 @@
 
     _flagserrorclass = error.RevlogError
 
+    @staticmethod
+    def is_inline_index(header_bytes):
+        header = INDEX_HEADER.unpack(header_bytes)[0]
+
+        _format_flags = header & ~0xFFFF
+        _format_version = header & 0xFFFF
+
+        features = FEATURES_BY_VERSION[_format_version]
+        return features[b'inline'](_format_flags)
+
     def __init__(
         self,
         opener,