When it comes to configuring MySQL, a fundamental step is to find out which configuration files the MySQL server reads.

The operation itself is simple, however, if we want to script the operation, using text processing in a sharp way, it’s not immediate what the best solution is.

In this post I’ll explore the process of looking for a satisfying solution, going through grep, perl, and awk.

Contents:

• Assumptions
• Input data (finding the configuration files read by MySQL)
• …

#!/bin/sh
# get.database.sizes.sh
# by dragkh
# Wed, 02 Mar 2011 17:59:44 +0100
# it will work on linux boxes with working mysql 
ps axu \
| grep datadir \
| grep mysql \
| grep -v grep \
| grep var \
| sed 's/^.*--datadir=//; s/ .*$//'   \
| sort \
| uniq  \
| while read crap
do 
echo ""
sized=$(du -s $crap | awk '{print $1}')
avail=$(df | grep $(dirname $crap) | awk '{print $2}')
echo -e  "$crap\t$sized\t$avail" | awk '{printf ("%s:\tUsed: %6.2fG \tDISK: %6.2fG\t Usage: %6.2f%% \n",$1,$2/1024/1024,$3/1024/1024,($2/$3)*100)}'
find $crap/ -maxdepth  1 -type d ! -type l  ! -path "$crap/"   -printf '"%p"\n'  | xargs  --no-run-if-empty  du -s | sort -nk 1,9 | awk -vavail=$avail '{crapy="";for(i=2; i<=NF; i++) {crapy=crapy" "$i;};printf (" -- %s\tUsed: %6.2fG \tDISK:%6.2fG Usage:%6.2f%%\n",crapy,$1/1024/1024,avail/1024/1024,($1/avail)*100)}'
done

result looks like

root@xxxx:[Wed Mar 02 16:54:59]:
/var/lib/mysql/aaaa/datafiles:               Used:  26.43G …

Recently I was working with the output of pstack from a hung MySQL server and wanted to use Poor Man's Profiler in order to combine stack traces. Unfortunately, the awk magic expects the output from gdb's thread apply all bt output.

gdb output:

Thread 10 (Thread 0xa644db90 (LWP 26275)):
#0  0xb7f47410 in __kernel_vsyscall ()
#1  0xb7f33b1a in do_sigwait () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb7f33bbf in sigwait () from /lib/tls/i686/cmov/libpthread.so.0
#3  0x081cc4fc in signal_hand ()
#4  0xb7f2b4fb in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#5  0xb7d25e5e in clone () from /lib/tls/i686/cmov/libc.so.6

Thread 9 (Thread 0xa641cb90 (LWP 26273)):
#0  0xb7f47410 in __kernel_vsyscall ()
#1  0xb7d1e881 in select …

[author's note: personally, I use awk a bunch in MySQL DBA work, for tasks like scrubbing data from a production export for use in qa/dev, but usually have to resort to Perl for really complex stuff, but now I know how to do .]

Basics:
By default, fields are separated by any number of spaces. The -F option to awk changes the separator on commandline.
Print the first field, fields are separated by a colon.
awk -F: '{print $1}' /etc/passwd

Print the first and fifth field:
awk -F: '{$print $1,$5}' /etc/passwd

Can pattern match and use files, so you can replace:
grep foo /etc/passwd | awk -F: '{print $1,$5}'
with:
awk -F: '/foo/ {print $1,$5}' /etc/passwd

NF = built in variable (no $) used to mean “field number”
This will print the first and last fields of lines where the first …

Recently I had an interesting issue crop up. Due to an unfortunate migration incident in which involved master/master replication and not checking to see if replication was caught up, we ended up with an infinite replication loop of a number of SQL statements. awk helped immensely in the aftermath cleanup.

The basics of the replication infinite loop were (more…)

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