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 >> >>
