diff mercurial/configitems.toml @ 51108:0250e45040f1

revlog: add a small cache of unfiltered chunk

This can provides a massive boost to the reading of multiple revision and the
computation of a valid delta chain.

This greatly help operation like `hg log --patch`, delta computation (helping
pull/unbundle), linkrev adjustment (helping copy tracing).

A first round of benchmark for `hg log --patch --limit 1000` shows improvement
in the 10-20% range on "small" repository like pypy or mercurial and large
improvements (about 33%) for more complex ones like netbeans and mozilla's.

These speeds up are consistent with the improvement to `hg pull` (from a server
sending poor deltas) I saw benchmarking this last year. Further benchmark will
be run during the freeze.

I added some configuration in the experimental space to be able to further test
the effect of various tuning for now. This feature should fit well in the
"usage/resource profile" configuration that we should land next cycle.

When it does not provides a benefit the overhead of the cache seem to be around
2%, a small price for the big improvement. In addition I believe we could shave
most of this overhead with a more efficent lru implementation.

--- a/mercurial/configitems.toml	Fri Oct 27 02:57:09 2023 +0200
+++ b/mercurial/configitems.toml	Fri Oct 27 08:54:41 2023 +0200
@@ -1111,6 +1111,28 @@
 
 [[items]]
 section = "experimental"
+name = "revlog.uncompressed-cache.enabled"
+default = true
+experimental = true
+documentation = """Enable some caching of uncompressed chunk, greatly boosting
+performance at the cost of memory usage."""
+
+[[items]]
+section = "experimental"
+name = "revlog.uncompressed-cache.factor"
+default = 4
+experimental = true
+documentation = """The size of the cache compared to the largest revision seen."""
+
+[[items]]
+section = "experimental"
+name = "revlog.uncompressed-cache.count"
+default = 10000
+experimental = true
+documentation = """The number of chunk cached."""
+
+[[items]]
+section = "experimental"
 name = "stream-v3"
 default = false