Sites loading slowly: high TTFB and CPU usage by Apache

Symptoms

1. High CPU usage by Apache is displayed in Health Monitor.

2. There is no DDOS attack on the server:

   # netstat -an | egrep ':80|:443' | grep ESTABLISHED | awk '{print $5}' | grep -o -E "([0-9]{1,3}[\.]){3}[0-9]{1,3}" | sort -n | uniq -c | sort -nr
   11 203.0.113.2
   8 203.0.113.5
   2 203.0.113.4

3. Time to first byte / Start transfer time for websites hosted on the server is high:

   # curl -s -w '\nLookup time:\t\t%{time_namelookup}\nConnect time:\t\t%{time_connect}\nSSL handshake time:\t%{time_appconnect}\nPre-Transfer time:\t%{time_pretransfer}\nRedirect time:\t\t%{time_redirect}\nTime to first byte:\t%{time_starttransfer}\n\nTotal time:\t\t%{time_total}\n' -o /dev/null http://example.com
   
   Lookup time: 0.001502
   Connect time: 0.120165
   SSL handshake time: 0.000000
   Pre-Transfer time: 0.120240
   Redirect time: 0.000000
   Time to first byte: 25.204602

4. Piped logs feature is enabled in Tools & Settings > Apache Web Server.

• In some cases, the following error message can be found in Apache error log /var/log/httpd/error_log:

  CONFIG_TEXT: [log_config:warn] [pid 5774] (32)Broken pipe: [client 203.0.113.2:43955] AH00646: Error writing to |/usr/local/psa/admin/sbin/pipelog 443, referer: http://example.com/

Cause

The enabled Piped logs feature slows down Apache performance.

Resolution

1. Log in to Plesk.

2. Disable the Piped logs feature in Tools & Settings > Apache Web Server.