On Fri, Feb 15, 2008 at 07:22:34PM +0300, Vsevolod Stakhov wrote:
> Hi,
>
> We found a problem with list requests_inflight while using evdns on
> highly loaded system (about 2000 DNS requests per second). First of all
> linear search is slow and second is that this list is not big enough to
> handle all requests, so many requests were in requests_waiting list,
> that has no limits on length. Due to this application grows in size
> constantly and is not able to serve requests. I've replaced linear list
> with hashed list, that improves performance.
Hi! This looks pretty good. I'd like to apply it for trunk to apply
it to the next release after 1.4. (I want to avoid applying anything
but straight bugfixes to 1.4 at this point, so that it can get out of
beta soon.) A few comments and questions:
- Instead of changing global_max_request_inflight in the code manually,
you can just call
evdns_set_option("max-inflight:", "2048", DNS_OPTIONS_ALL).
- Do you have profileing or benchmarking numbers to show how much this
helps? I'd like to be able to confirm that this helps, that "2048" is
a good value for MAX_NESTS, etc.
- It looks like we walk the whole inflight list on nameserver_failed(),
evdns_transmit(), evdns_clear_nameservers_and_suspend(), and
evdns_shutdown(). Of these, evdns_transmit() still worries me a
little: unlike the others, it is frequently called during
non-exceptional conditions. Does it show up in your profiles?
> The one thing that is not
> logical (but I don't know how to make it better) is that I'm using bzero
> of hash nests array in reading resolv conf function.
Probably it's better to do this in some function called from both
evdns_resolv_conf_parse() and evdns_config_windows_nameservers(). It
should probably use a flag to make sure that it hasn't already zeroed the
array.
Also, bzero() is deprecated in POSIX.1; you should probably use memset()
instead.
Please let me know what you think; I'd like to get a feature like this into
libevent.
yrs,
--
Nick
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