sync_freq.md 2.2 KB
Understand the alert
This alert is triggered when the number of sync() system calls is greater than 6. The sync() system call writes any data buffered in memory out to disk, including modified superblocks, modified inodes, and delayed reads and writes. A higher number of sync() calls indicates that the system is often trying to flush buffered data to disk, which can cause performance issues.
Troubleshoot the alert
- Identify the process causing sync events
Use bpftrace to identify which processes are causing the sync events. Make sure you have bpftrace installed on your system; if not, follow the instructions here: Installing bpftrace
Run the syncsnoop.bt script from the bpftrace tools:
sudo bpftrace /path/to/syncsnoop.bt
This script will trace sync events and display the process ID (PID), process name, and the stack trace.
- Analyze the output
Focus on processes with a high number of sync events, and investigate whether you can optimize these processes or reduce their impact on the system.
- Check if these processes are essential to system functionality.
- Look for potential bugs or misconfigurations that may trigger undue
sync()calls. - Consider modifying the process itself to reduce disk I/O or change how it handles write operations.
- Monitor your system's I/O performance
Keep an eye on overall I/O performance using tools like iostat, iotop, or vmstat.
For example, you can use iostat to monitor disk I/O:
iostat -xz 1
This command displays extended disk I/O statistics with a 1-second sampling interval.
Check for high await values, which indicate the average time taken for I/O requests to be completed. Look for high %util values, representing the percentage of time the device was busy servicing requests.