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  1. ZABBIX BUGS AND ISSUES
  2. ZBX-17762

Frequent TCP listen queue overflows

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Details

    • Problem report
    • Status: Closed
    • Trivial
    • Resolution: Duplicate
    • 4.4.7
    • None
    • Server (S)
    • FreeBSD stable/12 amd64

    Description

      First reported as ZBX-7933 , The zabbix agent frequently suffers TCP listen queue overflows, resulting in messages like "Mar 12 17:20:17 zabbix-p01 kernel: sonewconn: pcb 0xc809dad4: Listen queue overflow: 193 already in queue awaiting acceptance" printed to the system console.  While this is not a correctness issue, it is still a performance issue. All of those dropped TCP connections hurt performance. On my system, I find that when the maximum listen queue is very large, the backlog quickly spikes from 0 to 215 connections before plateauing. This strongly suggests that raising the listen queue size is the correct solution.

       

      The attached patch raises the listen queue from the old-fashioned SOMAXCONN to INT_MAX instead.  The operating system will limit the actual queue depth, of course.  On FreeBSD, the actual maximum queue depth is set by the kern.ipc.soacceptqueue sysctl.  SOMAXCONN is a fossil that doesn't have any real meaning anymore.

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              zabbix.support Zabbix Support Team
              asomers Alan Somers
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                Created:
                Updated:
                Resolved: