[Bug 1827923] Re: Constant sockmgr 0x7fa0b8b0a010: maximum number of FD events (64) received

Andreas Hasenack andreas at canonical.com
Mon May 6 18:23:42 UTC 2019

https://kb.isc.org/docs/aa-00716 is also helpful:
BIND 9.9.0 introduced multiple UDP listeners to improve performance, which means that in a multi-threaded BIND installation, there are effectively more sockets being monitored for client-side queries. If you are also listening on multiple interfaces (real or virtual), this might mean that # interfaces x # UDP listeners exceeds 64. The outcome of this is that on a busy server (particularly a busy recursive server that is also opening connections to make iterative queries of authoritative servers), the default number of FD events is already too small.

There are two options:
a) rebuild with a higher limit
b) reduce the number of UDP listeners

(b) is achieved with the -U command line option:

       -U #listeners
           Use #listeners worker threads to listen for incoming UDP packets on each address. If not specified, named will calculate a default value based on the number of detected CPUs: 1 for 1 CPU, and
           the number of detected CPUs minus one for machines with more than 1 CPU. This cannot be increased to a value higher than the number of CPUs. If -n has been set to a higher value than the number
           of detected CPUs, then -U may be increased as high as that value, but no higher. On Windows, the number of UDP listeners is hardwired to 1 and this option has no effect.

88 processors is probably not very common, and according to the above kb link, having more than 32 listeners might not increase performance at all. Could MAAS perhaps limit the number of listeners on such machines via this parameter? Notice it's this value per address.

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  Constant sockmgr 0x7fa0b8b0a010: maximum number of FD events (64)

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