> This is an API where it'd be ok to have a no-op if not implemented, correct? Or is there an requirement like Syncable that specific guarantees are met？
Yes I think it's ok to leave it as no-op for other non-HDFS FS impls: it is only used by HDFS standby reads so far. On Sun, Dec 13, 2020 at 4:58 AM Steve Loughran <[email protected]> wrote: > This isn't worth holding up the RC. We'd just add something to the > release notes "use with caution". And if we can get what the API does > defined in a way which works, it shouldn't need changing. > > (which reminds me, I do need to check that RC out, don't I?) > > On Sun, 13 Dec 2020 at 09:00, Xiaoqiao He <[email protected]> wrote: > >> Thanks Steve very much for your discussion here. >> >> Leave some comments inline. Will focus on this thread to wait for the >> final >> conclusion to decide if we should prepare another release candidate of >> 3.2.2. >> Thanks Steve and Chao again for your warm discussions. >> >> On Sat, Dec 12, 2020 at 7:18 PM Steve Loughran >> <[email protected]> >> wrote: >> >> > Maybe it's not in the release; it's certainly in the 3.2 branch. Will >> check >> > further. If it's in the release I was thinking of adding a warning in >> the >> > notes "unstable API"; stable if invoked from DFSClient >> >> On Fri, 11 Dec 2020 at 18:21, Chao Sun <[email protected]> wrote: >> > >> > > I'm just curious why this is included in the 3.2.2 release? >> HDFS-15567 is >> > > tagged with 3.2.3 and the corresponding HDFS-14272 on server side is >> > tagged >> > > with 3.3.0. >> > >> >> Just checked that HDFS-15567 has been involved in Hadoop-3.2.2 RC4. IIRC, >> I >> have cut branch-3.2.2 in early October, at that time branch-3.2.3 has >> created but source code not freeze completely because several blocked >> issues reported and code freeze has done about mid October. Some issues >> which are tagged with 3.2.3 has also been involved in 3.2.2 during >> that period, include HDFS-15567. I will check them later, and make sure >> that we have mark the correct tags. >> >> >> > > >> > > > If it goes into FS/FC, what does it do for a viewfs with >1 mounted >> > HDFS? >> > > Should it take path, msync(path) so that viewFS knows where to forward >> > it? >> > > >> > > The API shouldn't take any path - for viewFS I think it should call >> this >> > on >> > > all the child file systems. It might also need to handle the case >> where >> > > some downstream clusters support this capability while others don't. >> > > >> > >> > That's an extra bit of work for ViewFS then. It should probe for >> capability >> > and invoke as/when supported. >> > >> > > >> > > > Options >> > > 1. I roll HDFS-15567 back "please be follow process" >> > > 2. Someone does a followup patch with specification and contract test, >> > view >> > > FS. Add even more to the java >> > > 3. We do as per HADOOP-16898 into an MSyncable interface and then >> > > FileSystem & HDFS can implement. ViewFS and filterFS still need to >> pass >> > > through. >> > > >> > > I'm slightly in favor of the hasPathCapabilities approach and make >> this a >> > > mixin where FS impls can optionally support. Happy to hear what others >> > > think. >> > > >> > >> > Mixins are great when FC and FS can both implement; makes it easier to >> code >> > against either. All the filtering/aggregating FS's will have to >> implement >> > it, which means that presence of the interface doesn't guarantee >> support. >> > >> > This is an API where it'd be ok to have a no-op if not implemented, >> > correct? Or is there an requirement like Syncable that specific >> guarantees >> > are met? >> > >> > > >> > > Chao >> > > >> > > >> > > On Fri, Dec 11, 2020 at 9:00 AM Steve Loughran >> > <[email protected] >> > > > >> > > wrote: >> > > >> > > > Silence from the HDFS team >> > > > >> > > > >> > > > Hadoop 3.2.2 is in an RC; it has the new FS API call. I really don't >> > want >> > > > to veto the release just because someone pulled up a method without >> > doing >> > > > the due diligence. >> > >> >> Thanks Steve started this discussion here. I agree to roll back HDFS-15567 >> if there are still some incompatible issues not resolved completely. And >> release will not be the blocked things here, I would like to prepare >> another RC if we would reach common agreement. To be honest, I think it is >> better to involve Shvachko here. >> >> >> > > > Is anyone in the HDFS going to do that due diligence or should we >> > include >> > > > something in the release notes "msync()" must be considered >> unstable. >> > > > >> > > > Then we can do a proper msync(). >> > > > >> > > > If it goes into FS/FC, what does it do for a viewfs with >1 mounted >> > HDFS? >> > > > Should it take path, msync(path) so that viewFS knows where to >> forward >> > > it? >> > > > >> > > > Alternatively: go with an MSync interface which those few FS which >> > > > implement it (hdfs) can do that, and the fact that it doesn't have >> doc >> > or >> > > > tests won't be a blocker any more? >> > > > >> > > > -steve >> > > > >> > > > >> > > > >> > > > >> > > > On Thu, 10 Dec 2020 at 12:41, Steve Loughran <[email protected]> >> > > wrote: >> > > > >> > > > > >> > > > > Gosh, has it really been only since february since I last asked >> the >> > > HDFS >> > > > > dev list to stop adding anything to FileSystem/FileContext APIs >> > without >> > > > > >> > > > > * mentioning this on the hadoop-common list. >> > > > > * specifying what it does in filesystem.md >> > > > > * with a contract test >> > > > > * a new hasPathCapabilities probe. Throwing >> > > UnsupportedOperationException >> > > > > only lets people work out if it is unsupported through invocation. >> > > Being >> > > > > able to probe for it is better. >> > > > > * ViewFS support. >> > > > > * And, for any new API, one which works well for high-latency >> object >> > > > > stores: returning Future<Something> and >> > > Future<RemoteIterator<Something> >> > > > > when > 1 result is returned >> > > > > >> > > > > This needs to hold even for pulling something up from HDFS. >> Because >> > if >> > > > > another FS wants to implement it, they need to know what it does, >> and >> > > > have >> > > > > tests to verify this. I say this as someone who has tried to >> document >> > > > HDFS >> > > > > rename() semantics and gave up. >> > > > > >> > > > > It's really frustrating that every time someone does an FS API >> change >> > > > like >> > > > > this in the past (most recently HDFS-13616) I am the one who has >> to >> > > keep >> > > > > sending the reminders out, and then having to try and clean up/. >> > > > > >> > > > > So what now? >> > > > > >> > > > > Options >> > > > > 1. I roll HDFS-15567 back "please be follow process" >> > > > > 2. Someone does a followup patch with specification and contract >> > test, >> > > > > view FS. Add even more to the java >> > > > > 3. We do as per HADOOP-16898 into an MSyncable interface and then >> > > > > FileSystem & HDFS can implement. ViewFS and filterFS still need to >> > pass >> > > > > through. >> > > > > >> > > > > *If nobody is going to volunteer for the specification/test >> changes, >> > > I'm >> > > > > happy for the rollback. It'll remind people about process, * >> > > > > >> > > > > Pre-emptive Warning: No matter what we do for this patch, I will >> roll >> > > > back >> > > > > the next change which adds a new API if it's not accompanied by >> > > > > specification and tests. >> > > > > >> > > > > Unhappily yours, >> > > > > >> > > > > Steve >> > > > > >> > > > >> > > >> > >> >
