Thanks all Seems all concerns are related to the stage 2. We can address these and make it more clear before we start it.
>From development experience, I think it is reasonable to split the big feature into several stages. And stage 1 is also independent and it also can be as a minor feature that uses fs and bm locks instead of the global lock. ZanderXu <zande...@apache.org> 于2024年4月29日周一 15:17写道： > Thanks @Ayush Saxena <ayush...@gmail.com> and @Xiaoqiao He > <hexiaoq...@apache.org> for your nice questions. > > Let me summarize your concerns and corresponding solutions: > > *1. Questions about the Snapshot feature* > It's difficult to apply the FGL to Snapshot feature, but we can just using > the global FS write lock to make it thread safe. > So if we can identity if a path contains the snapshot feature, we can just > using the global FS write lock to protect it. > > You can refer to HDFS-17479 > <https://issues.apache.org/jira/browse/HDFS-17479> to get how to identify > it. > > Regarding performance of the operations related to the snapshot features, > we can discuss it in two categories: > Read operations involves snapshots: > The FGL branch uses the global write lock to protect them, the GLOBAL > branch uses the global read lock to protect them. It's hard to conclude > which version has better performance, it depends on the global lock > competition. > > Write operations involves snapshots: > Both FGL and GLOBAL branch use the global write lock to protect them. It's > hard to conclude which version has better performance, it depends on the > global lock competition too. > > So I think if namenode load is low, the GLOBAL branch will have a better > performance than FGL; If namenode load is high, the FGL branch may have a > better performance than the GLOBAL, which also depends on the ratio of read > and write operations on the SNAPSHOT feature. > > We can do somethings to let end-user to choose a branch with a better > branch according to their business: > First, we need to make the lock mode can be selectable, so that end-user > can choose to use FGL of GLOBAL. > Second, using the global write lock to make operations related to snapshot > thread safe as I described in HDFS-17479. > > > *2. Questions about the Symlinks feature* > If Symlink is related to snapshot, we can refer to the solution of the > snapshot; If Symlink is not related to snapshot, I think it's easy to meet > the FGL. > Only createSymlink involves two paths, FGL just need to lock them in the > order to make this operation thread. For other operations, it is the same > as other normal iNode, right? > > If I missed difficult points, please let me know. > > > *3. Questions about Memory Usage of iNode locks* > I think there are too many solutions to limit the memory usage of these > iNode locks, such as: Using a limit capacity lock pool to ensure the > maximum memory usage, Just holding iNode locks for fixed depth of > directories, etc. > > We can just abstract this LockManager first and then support its > implementation with different ideas, so that we can limit the maximum > memory usage of these iNode locks. > FGL can acquire or lease iNode locks through LockManager. > > > *4. Questions about Performance of acquiring and releasing iNode locks* > We can add some benchmark for LockManager, to test the performance or > acquire and release unblocked locks. > > > *5. Questions about StoragePolicy, ECPolicy, ACL, Quota, etc.* > These policies may be sot on an ancestor node and used by some children > files. The set operation for these policies will be protected by the > directory tree, since there are all file-related operations. In addition > to Quota and StoragePolicy, the use of other policies will also be > protected by directory tree, such as ECPolicy and ACL. > > Quota is a little special since its update operations may not be protected > by the directory tree, we can assign a locks to each QuotaFeature and use > these locks to make updating operations thread safe. you can refer to > HDFS-17473 <https://issues.apache.org/jira/browse/HDFS-17473> to get some > detailed information. > > StoragePolicy is a little special since it is used not only by file-related > operations but also block-related operations. ProcessExtraRedundancyBlock > uses storage policy to choose redundancy replicas and > BlockReconstructionWork uses storage policy to choose target DNs. In order > to maximize the performance improvement, BR and IBR should only involve the > iNodeFile to which the current processing block belongs. These redundancy > blocks can be processed by the Redundancy monitor while holding the > directory tree locks. You can refer to HDFS-17505 > <https://issues.apache.org/jira/browse/HDFS-17505> to get more detailed > informations. > > *6. Performance of the phase 1* > HDFS-17506 <https://issues.apache.org/jira/browse/HDFS-17506> is used to > do > some performance testing for phase 1, and I will complete it later. > > > Discuss solution through mails is not efficient, you can create one > sub-tasks under HDFS-17366 > <https://issues.apache.org/jira/browse/HDFS-17366> to describe your > concerns and I will try to give some answers. > > Thanks @Ayush Saxena <ayush...@gmail.com> and @Xiaoqiao He > <hexiaoq...@apache.org> again. > > > > On Mon, 29 Apr 2024 at 02:00, Ayush Saxena <ayush...@gmail.com> wrote: > > > Thanx Everyone for chasing this, Great to see some momentum around FGL, > > that should be a great improvement. > > > > I have some two broad categories: > > ** About the process:* > > I think in the above mails, there are mentions that phase one is complete > > in a feature branch & we are gonna merge that to trunk. If I am catching > it > > right, then you can't hit the merge button like that. To merge a feature > > branch. You need to call for a Vote specific to that branch & it > requires 3 > > binding votes to merge, unlike any other code change which requires 1. It > > is there in our Bylaws. > > > > So, do follow the process. > > > > ** About the feature itself:* (A very quick look at the doc and the Jira, > > so please take it with a grain of salt) > > * The Google Drive link that you folks shared as part of the first mail. > I > > don't have access to that. So, please open up the permissions for that > doc > > or share the new link > > * Chasing the design doc present on the Jira > > * I think we only have Phase-1 ready, so can you share some metrics just > > for that? Perf improvements just with splitting the FS & BM Locks > > * The memory implications of Phase-1? I don't think there should be any > > major impact on the memory in case of just phase-1 > > * Regarding the snapshot stuff, you mentioned taking lock on the root > > itself? Does just taking lock on the snapshot root rather than the FS > root > > works? > > * Secondly about the usage of Snapshot or Symlinks, I don't think we > > should operate under the assumptions that they aren't widely used or not, > > we might just not know folks who don't use it widely or they are just > users > > not the ones contributing. We can just accept for now, that in those > cases > > it isn't optimised and we just lock the entire FS space, which it does > even > > today, so no regressions there. > > * Regarding memory usage: Do you have some numbers on how much the memory > > footprint increases? > > * Under the Lock Pool: I think you are assuming there would be very few > > inodes where lock would be required at any given time, so there won't be > > too much heap consumption? I think you are compromising on the Horizontal > > Scalability here. I doubt if your assumption doesn't hold true, under > heavy > > read load by concurrent clients accessing different inodes, the Namenode > > will start giving memory troubles, that would do more harm than good. > > Anyway Namenode heap is way bigger problem than anything, so we should be > > very careful increasing load over there. > > * For the Locks on the inodes: Do you plan to have locs for each inode? > > Can we somehow limit that to the depth of the tree? Like currently we > take > > lock on the root, have a config which makes us take lock at Level-2 or 3 > > (configurable), that might fetch some perf benefits and can be used to > > control the memory usage as well? > > * What is the cost of creating these inode locks? If the lock isn't > > already cached it would incur some cost? Do you have some numbers around > > that? Say I disable caching altogether & then let a test load run, what > > does the perf numbers look like in that case > > * I think we need to limit the size of INodeLockPool, we can't let it > grow > > infinitely in case of heavy loads and we need to have some auto > > throttling mechanism for it > > * I didn't catch your Storage Policy problem. If I decode it right, the > > problem is like the policy could be set on an ancestor node & the > children > > abide by that & this is the problem, if that is the case then isn't that > > the case with ErasureCoding policies or even ACLs or so? Can you > elaborate > > a bit on that. > > > > > > Anyway, regarding the Phase-1. If you share (the perf numbers with proper > > details + Impact on memory if any) for just phase 1 & if they are good, > > then if you call for a branch merge vote for Phase-1 FGL, you have my > vote, > > however you'll need to sway the rest of the folks on your own :-) > > > > Good Luck, Nice Work Guys!!! > > > > -Ayush > > > > > > On Sun, 28 Apr 2024 at 18:32, Xiaoqiao He <hexiaoq...@apache.org> wrote: > > > >> Thanks ZanderXu and Hui Fei for your work on this feature. It will be > >> a very helpful improvement for the HDFS module in the next journal. > >> > >> 1. If we need any more review bandwidth, I would like to be involved > >> to help review if possible. > >> 2. From the design document there are still missing some detailed > >> descriptions such as snapshot, symbolic link and reserved etc as > mentioned > >> above. I think it will be helpful for newbies who want to be involved > >> if all corner > >> cases are considered and described. > >> 3. From slack, we plan to check into the trunk at this phase. I am not > >> sure > >> If it is the proper time, following the dev plan there are two steps > left > >> to > >> finish this feature from the design document, right? If that, I think we > >> should > >> postpone checking in when all plans are ready. Considering that there > are > >> many unfinished tries for this feature in history, I think postpone > >> checking > >> will be the safe way, another way it will involve more rebase cost if > you > >> keep > >> separate dev branch, however I think It is not one difficult thing for > >> you. > >> > >> Good luck and look forward to making that happen soon! > >> > >> Best Regards, > >> - He Xiaoqiao > >> > >> On Fri, Apr 26, 2024 at 3:50 PM Hui Fei <feihui.u...@gmail.com> wrote: > >> > > >> > Thanks for interest and advice on this. > >> > > >> > Just would like to share some info here > >> > > >> > ZanderXu leads this feature and he has spent a lot of time on it. He > is > >> the main developer in stage 1. Yuanboliu and Kokonguyen191 also took > some > >> tasks. Other developers (slfan1989 haiyang1987 huangzhaobo99 RocMarshal > >> kokonguyen191) helped review PRs. (Forgive me if I missed someone) > >> > > >> > Actually haiyang1987, Yuanboliu and Kokonguyen191 are also very > >> familiar with this feature. We discussed many details offline. > >> > > >> > Welcome to more people interested in joining the development and > review > >> of the stage 2 and 3. > >> > > >> > > >> > Zengqiang XU <xuzengqiang5...@gmail.com> 于2024年4月26日周五 14:56写道： > >> >> > >> >> Thanks Shilun for your response: > >> >> > >> >> 1. This is a big and very useful feature, so it really needs more > >> >> developers to get on board. > >> >> 2. This fine grained lock has been implemented based on internal > >> branches > >> >> and has gained benefits by many companies, such as: Meituan, > Kuaishou, > >> >> Bytedance, etc. But it has not been contributed to the community due > >> to > >> >> various reasons, such as there is a big difference between the > version > >> of > >> >> the internal branch and the community trunk branch, the internal > >> branch may > >> >> ignore some functions to make FGL clear, and the contribution needs a > >> lot > >> >> of work and will take many times. It means that this solution has > >> already > >> >> been practiced in their prod environment. We have also practiced it > in > >> our > >> >> prod environment and gained benefits, and we are also willing to > spend > >> a > >> >> lot of time contributing to the community. > >> >> 3. Regarding the benchmark testing, we don't need to pay more > >> attention to > >> >> whether the performance is improved by 5 times, 10 times or 20 times, > >> >> because there are too many factors that affect it. > >> >> 4. As I described above, this solution is already being practiced by > >> many > >> >> companies. Right now, we just need to think about how to implement it > >> with > >> >> high quality and more comprehensively. > >> >> 5. I firmly believe that all problems can be solved as long as the > >> overall > >> >> solution is right. > >> >> 6. I can spend a lot of time leading the promotion of this entire > >> feature > >> >> and I hope more people can join us in promoting it. > >> >> 7. You are always welcome to raise your concerns. > >> >> > >> >> > >> >> Thanks Shilun again, I hope you can help review designs and PRs. > Thanks > >> >> > >> >> On Fri, 26 Apr 2024 at 08:00, slfan1989 <slfan1...@apache.org> > wrote: > >> >> > >> >> > Thank you for your hard work! This is a very meaningful > improvement, > >> and > >> >> > from the design document, we can see a significant increase in HDFS > >> >> > read/write throughput. > >> >> > > >> >> > I am happy to see the progress made on HDFS-17384. > >> >> > > >> >> > However, I still have some concerns, which roughly involve the > >> following > >> >> > aspects: > >> >> > > >> >> > 1. While ZanderXu and Hui Fei have deep expertise in HDFS and are > >> familiar > >> >> > with related development details, we still need more community > >> member to > >> >> > review the code to ensure that the relevant upgrades meet > >> expectations. > >> >> > > >> >> > 2. We need more details on benchmarks to ensure that test results > >> can be > >> >> > reproduced and to allow more community member to participate in the > >> testing > >> >> > process. > >> >> > > >> >> > Looking forward to everything going smoothly in the future. > >> >> > > >> >> > Best Regards, > >> >> > - Shilun Fan. > >> >> > > >> >> > On Wed, Apr 24, 2024 at 3:51 PM Xiaoqiao He <hexiaoq...@apache.org > > > >> wrote: > >> >> > > >> >> >> cc private@h.a.o. > >> >> >> > >> >> >> On Wed, Apr 24, 2024 at 3:35 PM ZanderXu <zande...@apache.org> > >> wrote: > >> >> >> > > >> >> >> > Here are some summaries about the first phase: > >> >> >> > 1. There are no big changes in this phase > >> >> >> > 2. This phase just uses FS lock and BM lock to replace the > >> original > >> >> >> global > >> >> >> > lock > >> >> >> > 3. It's useful to improve the performance, since some operations > >> just > >> >> >> need > >> >> >> > to hold FS lock or BM lock instead of the global lock > >> >> >> > 4. This feature is turned off by default, you can enable it by > >> setting > >> >> >> > dfs.namenode.lock.model.provider.class to > >> >> >> > > >> org.apache.hadoop.hdfs.server.namenode.fgl.FineGrainedFSNamesystemLock > >> >> >> > 5. This phase is very import for the ongoing development of the > >> entire > >> >> >> FGL > >> >> >> > > >> >> >> > Here I would like to express my special thanks to @kokonguyen191 > >> and > >> >> >> > @yuanboliu for their contributions. And you are also welcome to > >> join us > >> >> >> > and complete it together. > >> >> >> > > >> >> >> > > >> >> >> > On Wed, 24 Apr 2024 at 14:54, ZanderXu <zande...@apache.org> > >> wrote: > >> >> >> > > >> >> >> > > Hi everyone > >> >> >> > > > >> >> >> > > All subtasks of the first phase of the FGL have been completed > >> and I > >> >> >> plan > >> >> >> > > to merge them into the trunk and start the second phase based > >> on the > >> >> >> trunk. > >> >> >> > > > >> >> >> > > Here is the PR that used to merge the first phases into trunk: > >> >> >> > > https://github.com/apache/hadoop/pull/6762 > >> >> >> > > Here is the ticket: > >> https://issues.apache.org/jira/browse/HDFS-17384 > >> >> >> > > > >> >> >> > > I hope you can help to review this PR when you are available > >> and give > >> >> >> some > >> >> >> > > ideas. > >> >> >> > > > >> >> >> > > > >> >> >> > > HDFS-17385 <https://issues.apache.org/jira/browse/HDFS-17385> > >> is > >> >> >> used for > >> >> >> > > the second phase and I have created some subtasks to describe > >> >> >> solutions for > >> >> >> > > some problems, such as: snapshot, getListing, quota. > >> >> >> > > You are welcome to join us to complete it together. > >> >> >> > > > >> >> >> > > > >> >> >> > > ---------- Forwarded message --------- > >> >> >> > > From: Zengqiang XU <zande...@apache.org> > >> >> >> > > Date: Fri, 2 Feb 2024 at 11:07 > >> >> >> > > Subject: Discussion about NameNode Fine-grained locking > >> >> >> > > To: <hdfs-dev@hadoop.apache.org> > >> >> >> > > Cc: Zengqiang XU <xuzengqiang5...@gmail.com> > >> >> >> > > > >> >> >> > > > >> >> >> > > Hi everyone > >> >> >> > > > >> >> >> > > I have started a discussion about NameNode Fine-grained > Locking > >> to > >> >> >> improve > >> >> >> > > performance of write operations in NameNode. > >> >> >> > > > >> >> >> > > I started this discussion again for serval main reasons: > >> >> >> > > 1. We have implemented it and gained nearly 7x performance > >> >> >> improvement in > >> >> >> > > our prod environment > >> >> >> > > 2. Many other companies made similar improvements based on > their > >> >> >> internal > >> >> >> > > branch. > >> >> >> > > 3. This topic has been discussed for a long time, but still > >> without > >> >> >> any > >> >> >> > > results. > >> >> >> > > > >> >> >> > > I hope we can push this important improvement in the community > >> so > >> >> >> that all > >> >> >> > > end-users can enjoy this significant improvement. > >> >> >> > > > >> >> >> > > I'd really appreciate you can join in and work with me to push > >> this > >> >> >> > > feature forward. > >> >> >> > > > >> >> >> > > Thanks very much. > >> >> >> > > > >> >> >> > > Ticket: HDFS-17366 < > >> https://issues.apache.org/jira/browse/HDFS-17366> > >> >> >> > > Design: NameNode Fine-grained locking based on directory tree > >> >> >> > > < > >> >> >> > >> > https://docs.google.com/document/d/1X499gHxT0WSU1fj8uo4RuF3GqKxWkWXznXx4tspTBLY/edit?usp=sharing > >> >> >> > > >> >> >> > > > >> >> >> > >> >> >> > >> --------------------------------------------------------------------- > >> >> >> To unsubscribe, e-mail: private-unsubscr...@hadoop.apache.org > >> >> >> For additional commands, e-mail: private-h...@hadoop.apache.org > >> >> >> > >> >> >> > >> > >> --------------------------------------------------------------------- > >> To unsubscribe, e-mail: hdfs-dev-unsubscr...@hadoop.apache.org > >> For additional commands, e-mail: hdfs-dev-h...@hadoop.apache.org > >> > >> >
