Today we have released PowerDNS Recursor 5.0.6.
This release is a maintenance release. The most important change is that the Recursor will warn if the Linux parameter vm.max_map_count is set too low to accommodate the maximum number of memory mappings used and reduce the maximum number of concurrent requests so that the Recursor will not hit the limit.
Each concurrent request uses an mthread. Starting with version 4.9 the way the mthread stacks are allocated has been changed to use the mmap system call. This allows for better memory protection, but uses a resource that is limited by the Linux kernel by the sysctl vm.max_map_count parameter. If this parameter is set too low, it can happen that the Recursor hits this limit and will not be able to allocate stacks for mthreads, resulting in degraded performance. This release warns for vm.max_map_count being too low and adjust the max-mthreads setting to avoid running out of mthreads.
Starting with version 4.9, it is advised to set sysctl vm.max_map_count to make sure that the Recursor can allocate enough stacks under load; suggested value is at least 4*(threads+2)*max-mthreads. Some Linux distributions use the value of about one million, which should be enough for most configurations. Other distributions default to 64k, which can be too low.
There are also a few other bug fixes and improvements, please refer to the changelogs (5.0.6) for additional details.
Please send us all feedback and issues you might have via the mailing list, or in case of a bug, via GitHub.
The tarball (5.0.6) (with signature files 5.0.6) are available from our download server and packages for several distributions are available from our repository.
Recently we made changes to our Open Source End of Life policy. Older release trains are now supported for one year after the following major release. Consult the EOL policy for more details.
We would also like to mention that with the 4.5 release we stopped supporting systems using 32-bit time. This includes many 32-bit Linux platforms.
We are grateful to the PowerDNS community for the reporting of bugs, issues, feature requests, and especially to the submitters of fixes and implementations of features.
