> Just to be clear for me. Is it correct to say that there is no difference in the "parent mark down" behavior between Consistent Hash and any of the other parent selection options (e.g. Round Robin)?
Correct. How it marks down and retries isn't related to the selection algorithm. All those settings are independent. Basically, any time a request comes in and it needs a parent, it says "get the first parent (whether that's via hash, round-robin, always-first, etc). Is this parent Down (and do we not want to retry it)? If not, use it. If so, get the next parent. Is that parent down? etc" Then, after it gets the request back, other configs determine whether it's a success (parent.config simple_server_retry_responses, unavailable_server_retry_responses, also see records.config negative_caching_list [which does not fail/markdown, but may be relevant to you]). But those settings are also independent of the parent selection algorithm or retry settings. On Tue, Aug 17, 2021 at 11:16 AM Nick Dunkin <nick.dun...@vecima.com.invalid> wrote: > Thanks Peter and Robert for all the input. Very useful information. > > Just to be clear for me. Is it correct to say that there is no difference > in the "parent mark down" behavior between Consistent Hash and any of the > other parent selection options (e.g. Round Robin)? > > Cheers, > > Nick > > On 8/17/21, 1:09 PM, "CHOU, PETER" <pc6...@att.com> wrote: > > Hi, > > There is no background thread checking on the original parent. Once the > original parent is marked down, the parent selection process will > ignore > it until it becomes retryable after a time-out period. > > This is configurable using the > "proxy.config.http.parent_proxy.retry_time" setting. > > Thanks, > Peter > > From: Nick Dunkin <nick.dun...@vecima.com.INVALID> > Sent: Tuesday, August 17, 2021 8:40 AM > To: dev@trafficserver.apache.org > Subject: Question about Consistent Hash and parent retry > > Hi, > > I have a question about Consistent Hash behavior when a parent is > “down”. This is ATS 7.1 > > The documentation states the following: “If a parent is down, the > traffic that would go to the down parent is rehashed amongst the remaining > parents. The other traffic is unaffected. Once the downed parent becomes > available, the traffic distribution returns to the pre-down state.” > > That second section implies that maybe: > > * A background thread is periodically retying the original hashed > parent, in order to mark it back up > * The original hashed parent is being retried on every access > until it is available again > > Please can someone clarify the exact behavior around Consistent Hash > and unavailable parents? The context here is that we believe we are seeing > the retries on the originally hashed parent occur more often than we would > expect. > > Many thanks, > > Nick > > Nick Dunkin > Director, Software Engineering > Manager – Architecture and New Product Introduction > o: +1 678.258.4071 > e: nick.dun...@vecima.com<mailto:nick.dun...@vecima.com> > > [cidimage001.png@01D6CC8C.6FC5A580] > > >
