In this blog, we’ll look at how the hidepid options for /proc and Percona XtraDB Cluster can fight with one another.

One of the things I like about consulting at Percona is the opportunity to be exposed to unusual problems. I recently worked with a customer having issues getting SST to work with Percona XtraDB Cluster. A simple problem you would think. After four hours of debugging, my general feeling was that nothing made sense.

I added a bash trace to the SST script and it claimed MySQL died prematurely:

[ -n '' ]]
+ ps -p 11244
+ wsrep_log_error 'Parent mysqld process (PID:11244) terminated unexpectedly.'
+ wsrep_log '[ERROR] Parent mysqld process (PID:11244) terminated unexpectedly.'
++ date '+%Y-%m-%d %H:%M:%S'
+ local readonly 'tst=2017-11-28 22:02:46'

At the same time, from the MySQL error log MySQL was …

In my last blog post, I showed how we can get some raw performance information from /proc into the MySQL database using a LOAD DATA INFILE (LDI) command.

I've modified that LDI call slightly to set the `other` column to equal the sum total of the CPU counters for those rows which begin with 'cpu'.

original:
other = IF(@the_key like 'cpu%', NULL , @val1);

new:
other = IF(@the_key like 'cpu%', user + nice + system + idle + iowait + irq + softirq + steal + guest, @val1);


Top provides a useful output that looks something like the following:

top - 04:59:14 up 14 days,  3:34,  1 user,  load average: 0.00, 0.00, 0.00
Tasks: 216 total,   1 running, 215 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.0%sy,  0.0%ni, 99.9%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8172108k total,  5115388k used,  3056720k free,   315180k buffers
Swap:  2097144k total,        0k …