Linux command pipeline buffer

This is a problem of Wang Gong.

MySQL monitoring indicators. Use mysqladmin to get the information every second, format the information and output the file.

Commands for getting information and formatting

Mysqladmin-uroot-proot-S mysql.sock ext-i1 | awk'/ Queries/ {QPX QPP 4} / Threads_connected/ {tc=$4} / Threads_running/ {printf "% 5d% 5d% 5d\ n", Q, tc, $4}'

This command can be carried out alone.

But if you want to redirect to a file, this information is not real-time. It takes more than ten seconds to write to the file.

Mysqladmin-uroot-proot-S mysql.sock ext-i1 | awk'/ Queries/ {qptince4} / Threads_connected/ {tc=$4} / Threads_running/ {printf "% 5d% 5d% 5d\ n", Q, tc, $4}'> a.log

Why can real-time output be achieved by directly executing the command, but redirection is delayed output?

This problem should also exist in tail-f.

After searching the data, it was found that it was the problem of the buffer zone.

Related links:

Https://aicode.cc/wei-shen-me-ni-de-ming-ling-xing-cheng-xu-mei-you.html

So the rewriting command can realize the requirement of real-time output.

Mysqladmin-uroot-proot-S mysql.sock ext-i1 | stdbuf-oL awk'/ Queries/ {Threads_connected/ tc=$4} / Threads_running/ {printf "% 5d% 5d% 5d\ n", Q, tc, $4}'> / tmp/mysql.log