2006 USENIX Annual Technical Conference Abstract
Pp. 115–128 of the Proceedings
Implementation and Evaluation of Moderate Parallelism in the BIND9 DNS Server
Tatuya Jinmei, Toshiba Corporation; Paul Vixie, Internet Systems Consortium
Abstract
Suboptimal performance of the ISC BIND9 DNS server with multiple threads is a
well known problem.
This paper explores practical approaches addressing this long-standing issue.
First, intensive profiling identifies major bottlenecks occurring due to
overheads for thread synchronization.
These bottlenecks are then eliminated by giving separate
work areas with a large memory pool to threads,
introducing faster operations on reference counters, and
implementing efficient reader-writer locks.
Whereas some of the solutions developed depend on atomic operations
specific to hardware architecture, which are less portable, the resulting
implementation still supports the same platforms as before through
abstract APIs.
The improved implementation scales well with up to four processors
whether it is operating as an
authoritative-only DNS server, with or without dynamic updates, or as a
caching DNS server. It also reduces the memory footprint for large
DNS databases.
Acceptance of this new sever will also have a positive side effect in that BIND9, and its new features such
as DNSSEC, should get wider acceptance.
The direct result has other ramifications: first, the better
performance at the application level reveals a kernel bottleneck
in FreeBSD; also, while the results described here are based on our experience
with BIND9, the techniques should be applicable to other thread-based
applications.
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