tail: fix stdin redirect (#3842) #3845
Conversation
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cool, bravo |
Thanks. |
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Bummer, $ cat tests/tail-2/start-middle.sh
(echo 1; echo 2) > k || framework_failure_
sh -c 'read x; tail' < k > out || fail=1
cat <<EOF > exp
2
EOF
compare exp out || fail=1This is tricky. Now we tail the the whole file ("1\n2\n"), but we're expected to only tail "2\n". @tertsdiepraam Do you have an idea for this issue? |
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Okay I figured out how to handle this issue. |
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This is ready now. Benchmarks for comparison: Summary
'cat 505MB.txt | tail -n 10000' ran
1.22 ± 0.11 times faster than 'cat 505MB.txt | tail -n 100000'
1.47 ± 0.09 times faster than 'cat 505MB.txt | tail -n 1000000'
1.70 ± 0.21 times faster than 'cat 505MB.txt | target/release/tail -n 10000'
2.12 ± 0.20 times faster than 'cat 505MB.txt | target/release/tail -n 100000'
4.89 ± 0.29 times faster than 'cat 505MB.txt | target/release/tail -n 1000000'
Summary
'tail -n 10000 505MB.txt' ran
1.51 ± 0.43 times faster than 'target/release/tail -n 10000 505MB.txt'
5.74 ± 1.19 times faster than 'tail -n 100000 505MB.txt'
9.37 ± 2.23 times faster than 'target/release/tail -n 100000 505MB.txt'
47.04 ± 9.29 times faster than 'tail -n 1000000 505MB.txt'
60.93 ± 13.18 times faster than 'target/release/tail -n 1000000 505MB.txt'
Summary
'tail -n 10000 < 505MB.txt' ran
1.41 ± 0.40 times faster than 'target/release/tail -n 10000 < 505MB.txt'
4.27 ± 1.05 times faster than 'tail -n 100000 < 505MB.txt'
6.99 ± 1.71 times faster than 'target/release/tail -n 100000 < 505MB.txt'
30.48 ± 7.43 times faster than 'tail -n 1000000 < 505MB.txt'
42.79 ± 10.05 times faster than 'target/release/tail -n 1000000 < 505MB.txt'I don't think the failing tests are related to this PR. |
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I opened #3890 for the chgrp issue Well done for the change. Any idea how we could be even closer to GNU's in term of perf ? |
I think that's what @Joining7943 is working on here: #3874 |
This fixes a bug where calling `tail - < file.txt` would result in invoking `unbounded_tail()`. However, it is a stdin redirect to a seekable regular file and therefore `bounded_tail` should be invoked as if `tail file.txt` had been called.
Previously, if stdin redirect pointed to a regular file, tailing started at the beginning of the file. However, tailing needs to start at the current position because this is expected by tests/tail-2/start-middle.sh. This fixes the issue by taking the current offset into account while going backwards through the stdin redirected file.
This fixes a bug where calling
tail - < file.txtwould resultin invoking
unbounded_tail().However, it is a stdin redirect to a seekable regular file and
therefore
bounded_tailshould be invoked as iftail file.txthadbeen called.
fix #3842