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Updated perf notes

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Bruce Hill 2021-08-01 22:06:45 -07:00
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README.md
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@ -147,19 +147,20 @@ File | Description
## Performance
Currently, `bp` is super slow compared to hyper-optimized regex tools like
`grep` and `ripgrep`. `bp` is **not** matching regular expressions, so this is
not strictly a fair comparison. By definition, regular expressions can be
implemented using finite state machines, which are very efficient. Most regex
tools also add the additional restriction that matches must be within a single
line. `bp` on the other hand, uses parsing expression grammars, which can match
arbitrarily complicated or nested structures, requiring a dynamic call stack
and potentially unbounded memory use. This makes `bp` patterns much more
expressive, but harder to optimize. At this point in time, `bp`'s
implementation also uses a fairly naive virtual machine written in C, which is
not very heavily optimized. As a result, `bp` runs quite fast over thousands of
lines of code, reasonably fast over tens of thousands of lines of code, and
pretty slow over millions of lines of code.
Currently, `bp`'s speed is comparable to hyper-optimized regex tools like
`grep`, `ag`, and `ripgrep` when it comes to simple patterns that begin with
string literals, but `bp`'s performance may be noticeably slower for complex
patterns on large quantities of text. The aforementioned regular expression
tools are usually implemented as efficient finite state machines, but `bp` is
more expressive and capable of matching arbitrarily nested patterns, which
precludes the possibility of using a finite state machine. Instead, `bp` uses a
fairly simple recursive virtual machine implementation with memoization. `bp`
also has a decent amount of overhead because of the metadata used for
visualizing and explaining pattern matches, as well as performing string
replacements. Overall, I would say that `bp` is a great drop-in replacement for
common shell scripting tasks, but you may want to keep the other tools around
in case you have to search through a truly massive codebase for something
complex.
## License