revset: rename rev argument of followlines() to startrev The rev argument has the same meaning as startrev of follow(), and I think startrev is more informative. followlines() is new function, we can make BC now.

help: use :hg: role and canonical name to point to revset string patterns Follows up 5dd67f0993ce. Now revisions.txt and revsets.txt has been merged, so use revisions.* as a pointer.

util: compression APIs to support revlog decompression Previously, compression engines had APIs for performing revlog compression but no mechanism to perform revlog decompression. This patch changes that. Revlog decompression is slightly more complicated than compression because in the compression case there is (currently) only a single engine that can be used at a time. However for decompression, a revlog could contain chunks from multiple compression engines. This means decompression needs to map to multiple engines and decompressors. This functionality is outside the scope of this patch. But it drives the decision for engines to declare a byte header sequence that identifies revlog data as belonging to an engine and an API for obtaining an engine from a revlog header.

crecord: add an experimental option for space key to move cursor down I really want to have an option of toggling a selection on a line and also moving cursor down as a single keystroke. It also kinda makes sense for space key to do this, because some other curses UIs in the wild do this (e.g. various file managers, htop). So I got an idea to make a config option that defaults to False for compatibility, but allows making crecord UI a lot more useful for people with big hunks. We add this an experimental option to experiment with this behavior.

perf: support multiple compression engines in perfrevlogchunks Now that the revlog has a reference to a compressor, it is possible to swap in other compression engines. So, teach `hg perfrevlogchunks` to do that. The default behavior of `hg perfrevlogchunks` is now to measure the compression performance of all compression engines implementing the revlog compressor API. This effectively adds the no-op "none" compressor and zstd (when available) into the default set. While we can't yet plug alternate compressors into revlogs, this command gives us a preview of the performance. On the mozilla-unified repository: $ hg perfrevlogchunks -c ! compress w/ none ! wall 0.115159 comb 0.110000 user 0.110000 sys 0.000000 (best of 86) ! compress w/ zlib ! wall 5.681406 comb 5.680000 user 5.680000 sys 0.000000 (best of 3) ! compress w/ zstd ! wall 2.624781 comb 2.620000 user 2.620000 sys 0.000000 (best of 4) $ hg perfrevlogchunks -m ! compress w/ none ! wall 0.124486 comb 0.120000 user 0.120000 sys 0.000000 (best of 79) ! compress w/ zlib ! wall 10.144701 comb 10.150000 user 10.150000 sys 0.000000 (best of 3) ! compress w/ zstd ! wall 4.383118 comb 4.390000 user 4.390000 sys 0.000000 (best of 3) Those numbers for zstd look promising. But they aren't the full story. For that, we'll need to look at decompression times and storage sizes. Stay tuned...

revlog: use compression engine API for compression This commit swaps in the just-added revlog compressor API into the revlog class. Instead of implementing zlib compression inline in compress(), we now store a cached-on-first-use revlog compressor on each revlog instance and invoke its "compress()" method. As part of this, revlog.compress() has been refactored a bit to use a cleaner code flow and modern formatting (e.g. avoiding parenthesis around returned tuples). On a mozilla-unified repo, here are the "compress" times for a few commands: $ hg perfrevlogchunks -c ! wall 5.772450 comb 5.780000 user 5.780000 sys 0.000000 (best of 3) ! wall 5.795158 comb 5.790000 user 5.790000 sys 0.000000 (best of 3) $ hg perfrevlogchunks -m ! wall 9.975789 comb 9.970000 user 9.970000 sys 0.000000 (best of 3) ! wall 10.019505 comb 10.010000 user 10.010000 sys 0.000000 (best of 3) Compression times did seem to slow down just a little. There are 360,210 changelog revisions and 359,342 manifest revisions. For the changelog, mean time to compress a revision increased from ~16.025us to ~16.088us. That's basically a function call or an attribute lookup. I suppose this is the price you pay for abstraction. It's so low that I'm not concerned.

util: compression APIs to support revlog compression As part of "zstd all of the things," we need to teach revlogs to use non-zlib compression formats. Because we're routing all compression via the "compression manager" and "compression engine" APIs, we need to introduction functionality there for performing revlog operations. Ideally, revlog compression and decompression operations would be implemented in terms of simple "compress" and "decompress" primitives. However, there are a few considerations that make us want to have a specialized primitive for handling revlogs: 1) Performance. Revlogs tend to do compression and especially decompression operations in batches. Any overhead for e.g. instantiating a "context" for performing an operation can be noticed. For this reason, our "revlog compressor" primitive is reusable. For zstd, we reuse the same compression "context" for multiple operations. I've measured this to have a performance impact versus constructing new contexts for each operation. 2) Specialization. By having a primitive dedicated to revlog use, we can make revlog-specific choices and leave the door open for more functionality in the future. For example, the zstd revlog compressor may one day make use of dictionary compression. A future patch will introduce a decompress() on the compressor object. The code for the zlib compressor is basically copied from revlog.compress(). Although it doesn't handle the empty input case, the null first byte case, and the 'u' prefix case. These cases will continue to be handled in revlog.py once that code is ported to use this API.