Benchmarking tac

tac is often used to process log files in reverse chronological order, i.e. from newer towards older entries. In this case, the performance target to yield results as fast as possible, i.e. without reading in the whole file that is to be reversed line-by-line. Therefore, a sensible benchmark is to read a large log file containing N lines and measure how long it takes to produce the last K lines from that file.

Large text files can for example be found in the Wikipedia database dumps, usually sized at multiple gigabytes and comprising more than 100M lines.

After you have obtained and uncompressed such a file, you need to build tac in release mode

cargo build --release --package uu_tac

and then you can time how it long it takes to extract the last 10M lines by running

/usr/bin/time ./target/release/tac wikidatawiki-20211001-pages-logging.xml | head -n10000000 >/dev/null

For more systematic measurements that include warm-ups, repetitions and comparisons, Hyperfine can be helpful. For example, to compare this implementation to the one provided by your distribution run

hyperfine "./target/release/tac wikidatawiki-20211001-pages-logging.xml | head -n10000000 >/dev/null" "/usr/bin/tac wikidatawiki-20211001-pages-logging.xml | head -n10000000 >/dev/null"