Re: Replication on the backend
От | J. Andrew Rogers |
---|---|
Тема | Re: Replication on the backend |
Дата | |
Msg-id | 3FA96BF2-6A09-48FD-9695-381AC1513A10@neopolitan.com обсуждение исходный текст |
Ответ на | Re: Replication on the backend (Markus Schiltknecht <markus@bluegap.ch>) |
Список | pgsql-hackers |
On Dec 6, 2005, at 11:42 PM, Markus Schiltknecht wrote: > Does anybody have latency / roundtrip measurements for current > hardware? > I'm interested in: > 1Gb Ethernet, > 10 Gb Ethernet, > InfiniBand, > probably even p2p usb2 or firewire links? In another secret life, I know a bit about supercomputing fabrics. The latency metrics have to be thoroughly qualified. First, most of the RTT latency numbers for network fabrics are for 0 byte packet sizes, which really does not apply to anyone shuffling real data around. For small packets, high-performance fabrics (HTX Infiniband, Quadrics, etc) have approximately an order of magnitude less latency than vanilla Ethernet, though the performance specifics depend greatly on the actual usage. For large packet sizes, the differences in latency become far less obvious. However, for "real" packets a performant fabric will still look very good compared to disk systems. Switched fiber fabrics have enough relatively inexpensive throughput now to saturate most disk systems and CPU I/O busses; only platforms like HyperTransport can really keep up. It is worth pointing out that the latency of high-end network fabrics is similar to large NUMA fabrics, which exposes some of the limits of SMP scalability. As a point of reference, an organization that knows what they are doing should have no problem getting 500 microsecond RTT on a vanilla metropolitan area GigE fiber network -- a few network operators actually do deliver this on a regional scale. For a local cluster, a competent design can best this by orders of magnitude. There are a number of silicon limitations, but a system that connects the fabric directly to HyperTransport can drive several GB/s with very respectable microsecond latencies if the rest of the system is up to it. There are Opteron system boards now that will drive Infiniband directly from HyperTransport. I know Arima/Rioworks makes some (great server boards generally), and several other companies are either making them or have announced them in the pipeline. These Opteron boards get pretty damn close to Big Iron SMP fabric performance in a cheap package. Given how many companies have announced plans to produce Opteron server boards with Infiniband fabrics directly integrated into HyperTransport, I would say that this is the future of server boards. And if postgres could actually use an infiniband fabric for clustering a single database instance across Opteron servers, that would be very impressive... J. Andrew Rogers
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