BTW, there is a Slack channel hdfs-fgl for this feature. can join it and discuss more details.
Is it necessary to hold a meeting to discuss this? So that we can push it forward quickly. Agreed with ZanderXu, it seems inefficient to discuss details via email list. Hui Fei <feihui.u...@gmail.com> 于2024年5月6日周一 23:50写道： > 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 >> >> >> >> >> >
