What is the meaning of «AH00485: scoreboard is full, not at MaxRequestWorkers»?

por | 29 marzo, 2022

My Environment

  • CentOS 6.4 X86_64
  • Apache 2.4.4
  • PHP 5.4.16 (FPM)
  • 2 Intel Xeon E5-2620 @ 2.00GHz (8 core, 16 threads in each processor)
  • 48GB RAM registered memory.
  • 3 Hard Disk 15RPM 145GB in RAID0 (by BIO

Interesting Variables

    <IfModule mpm_event_module>
        StartServers             2
        ThreadLimit             196
        MinSpareThreads         96
        MaxSpareThreads        192
        ThreadsPerChild         96
        MaxRequestWorkers      192
        MaxConnectionsPerChild   96

We had the same problem on Apache 2.4.6. After monitoring the server and adjusting the setting for several hours it appears to us that Apache may have a bug. What appears to happen is that the server processes occasionally goes into the G state (Gracefully finishing) and restarts to accept new requests, that’s normal. What is not normal is that for some reason this can take up to a few minutes to restart. If you only have a few server process running and they all go into the G state at the same time then your scoreboard fills up and you won’t be able to server any more requests.

What we did was increase the number of servers so there is a less of a chance that they will all go into the G state at the same time. Also make sure you allocate at least 25 threads (MaxRequestWorkers) for each server process because that appears to be the default (i.e. if 5 Servers x 25 ThreadsPerChild = 125 MaxRequestWorkers). You can change ThreadsPerChild if you like, we left it at default. If you don’t allocate enough threads the additional servers will not start. We left MinSpareThreads at the default value which is 25 and the default for MaxSpareThreads which is 75. If you do modify these settings, the value for MaxSpareThreads must be greater than or equal to the sum of MinSpareThreads and ThreadsPerChild. Also MaxRequestWorkers must be equal to or less than the ServerLimit.

Here is what worked for us but it might not be the best configuration for you.

StartServers 3
MinSpareServers 5
MaxSpareServers 10
ServerLimit 250
MaxRequestWorkers 250
MaxConnectionsPerChild 1000
KeepAlive Off

Edit: This is a confirmed bug in httpd’s mpm_event module which might not be fixable through configuration.
The linked bugtracker entry has a presumed patch and more discussion about how to fix this until a new version of the event module is officially released.