On Fri, 21 Apr 2023 18:23:07 GMT, Sergey Bylokhov <s...@openjdk.org> wrote:
>> I would like to get preliminary feedback about the provided patch. >> >> Discussion on net-dev@ >> https://mail.openjdk.org/pipermail/net-dev/2023-March/020682.html >> >> One of the main issue I try to solve is how the cache handle the >> intermittent DNS server outages due to overloading or network connection. >> >> At the moment this cache can be configured by the application using the >> following two properties: >> (1) "networkaddress.cache.ttl"(30 sec) - cache policy for successful >> lookups >> (2) "networkaddress.cache.negative.ttl"(10 sec) - cache policy for >> negative lookups >> >> The default timeout for positive responses is good enough to "have recent >> dns-records" and to "minimize the number of requests to the DNS server". >> >> But the cache for the negative responses is problematic. This is a problem I >> would like to solve. Caching the negative response means that for **10** >> seconds the application will not be able to connect to the server. >> >> Possible solutions: >> 1. Decreasing timeout "for the negative responses": unfortunately more >> requests to the server at the moment of "DNS-outage" cause even more issues, >> since this is not the right moment to load the network/server more. >> 2. Increasing timeout "for the positive responses": this will decrease the >> chance to get an error, but the cache will start to use stale data longer. >> 3. This proposal: it would be good to ignore the negative response and >> continue to use the result of the last "successful lookup" until some >> additional timeout. >> >> The idea is to split the notion of the TTL and the timeout used for the >> cache. When TTL for the record will expire we should request the new data >> from the server. If this request goes fine we will update the record, if it >> fails we will continue to use the cached date until the next sync. >> >> For example, if the new property "networkaddress.cache.extended.ttl" is set >> to 10 minutes, then we will cache a positive response for 10 minutes but >> will try to sync it every 30 seconds. If the new property is not set then as >> before we will cache positive for 30 seconds and then cache the negative >> response for 10 seconds. >> >> >> RFC 8767 Serving Stale Data to Improve DNS Resiliency: >> https://www.rfc-editor.org/rfc/rfc8767 >> >> Comments about current and other possible implementations: >> * The code intentionally moved to the separate ValidAddresses class, just >> to make clear that the default configuration, when the new property is not >> set is not changed much. >> * The refresh timeout includes the time spent on the server lookup. So if >> we have to refresh every 2 seconds, but in lookup, we spend 3 seconds then >> we will request the server on each lookup. Another implementation may spend >> 3 seconds on lookup and then additional use the cached value for two seconds. >> * The extended timeout is a kind of "maximum stale timer" from the RFC >> above, but it starts counting not from the moment the record expired, but >> from the moment we added it to the cache. Another possible implementation >> may start counting from the moment the TTL expired, so the overall usage of >> the value will be sum ttl+extended. >> * The extended timeout has a hard deadline which is never changed during >> execution, for example, if it sets for 1 day, then at the end of the day we >> should make a successful lookup to recache the value otherwise we will start >> to use the "negative" cache. Other implementations may shift the expiration >> time on every successful sync. >> >> Any thoughts about other possibilities? > > Sergey Bylokhov has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains 10 additional > commits since the last revision: > > - Merge branch 'master' into JDK-8304885 > - documentation > - PR feedback > - Merge remote-tracking branch 'upstream/master' into JDK-8304885 > - Use "maximum stale timer" instead of the extended timeout, and bump it on > each successful lookup > - the suggested cap is 7 days > - simplify > - comments > - Merge remote-tracking branch 'upstream/master' into JDK-8304885 > - 8304885: Reuse stale data to improve DNS resolver resiliency The comments were updated as requested. I have also merged the master to make sure the GitHub actions will be green. ------------- PR Comment: https://git.openjdk.org/jdk/pull/13285#issuecomment-1527016566
