[string] Chunk reads #4610
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[string] Chunk reads #4610
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Profiling with callgrind revealed that about 60% of the time in a `something | string match` call was actually spent in `string_get_arg_stdin()`, because it was calling `read` one byte at a time. This makes it read in chunks similar to builtin read. This increases performance for `getent hosts | string match -v '0.0.0.0*'` from about 300ms to about 30ms (i.e. 90%). At that point it's _actually_ quicker than `grep`. To improve performance even more, we'd have to cut down on str2wcstring.
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Urgh, I need to attribute https://stackoverflow.com/questions/1583353/how-to-read-exactly-one-line/1584620#1584620, which this is based on. |
ridiculousfish
approved these changes
Dec 19, 2017
src/builtin_string.cpp
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| // Read in chunks from fd until buffer has a line. | ||
| std::string::iterator pos; | ||
| while ((pos = std::find (buffer.begin(), buffer.end(), '\n')) == buffer.end ()) { |
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This is a bit more idiomatic as:
size_t pos;
while ((pos = buffer.find('\n')) == std::string::npos) {...
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THAT WAS IT! I've been thinking that there was some nicer way to to find, but I couldn't for the life of me come up with it.
src/builtin_string.cpp
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| *storage = str2wcstring(arg); | ||
| return storage->c_str(); | ||
| // Split the buffer around '\n' found and return first part. | ||
| *storage = str2wcstring(buffer.c_str(), std::distance(buffer.begin(), pos)); |
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With the above this could be simply *storage = str2wcstring(buffer, pos);
src/builtin_string.cpp
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| return storage->c_str(); | ||
| // Split the buffer around '\n' found and return first part. | ||
| *storage = str2wcstring(buffer.c_str(), std::distance(buffer.begin(), pos)); | ||
| buffer = std::string(pos + 1, buffer.end()); |
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and this could be buffer.erase(0, pos + 1);
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I think with my suggestions we can skip the attributions |
faho
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Description
Profiling with callgrind revealed that about 60% of the time in a
something | string matchcallwas actually spent in
string_get_arg_stdin(),because it was calling
readone byte at a time.This makes it read in chunks similar to builtin read.
This increases performance for
getent hosts | string match -v '0.0.0.0*'from about 300ms to about 30ms (i.e. 90%).At that point it's actually quicker than
grep.To improve performance even more, we'd have to cut down on str2wcstring.
Fixes issue #4604.
TODOs: