Hello Mulugeta, Igniters. Thanks for your interest and efforts in integrating the persistent memory to Ignite. Here are my thoughts on the PR:
First of all I was questioning whether we want to use the integration with the pmem library via JNI. Java 14 will have native support for NVME via native mapped byte buffers [1] since the corresponding tickets are already resolved [2],[3]. The suggested integration uses JNI calls quite often (if I read the PR right, there will be tens of JNI calls per a single operation), which may and most likely will undermine the benefits of using PM. On the other hand, there is a PoC/project [4] which successfully demonstrates how the new integration can be used to natively access persistent memory from Java. Additionally, new Unsafe have several performance issues - each put* methods has a map lookup, and CAS method uses a global lock. Removing these issues will change the PR and architecture dramatically. Other than performance and an extra library dependency, there are additional reasons to use custom implementation of PM persistence primitives: - Ignite significantly benefits from having WAL as a single point of data for both failure recovery and historical rebalance. As far as I can guess, the suggested library also uses some sort of journaling in order to support crash recovery. Since we do not want give up on the historical rebalance, we would need to write an additional journal, which then raises a question of how to transact between this journal. - Ignite is supposed to work with large indexes, a I not aware how LLPL handles them. Several researches [5],[6] show that since PM memory has larger access latency than regular RAM, it is beneficial to buffer index pages in regular memory and store leaf pages in PM. There is a generic approach to convert in-memory indexes to PM ones [7], I think it makes sense to investigate whether our existing indexes can be converted to PM. - There is an active IEP which is targeted for a file-based rebalancing. In the suggested implementation this optimization would not work. A better integration should allow to take a snapshot of a partition and transfer it to another node for fast rebalancing. Overall, I think we may take the following path: - Target JEP352 APIs; for now keep using the whole region msync for flush - Introduce PM-based isolated components to support WAL iterator and transaction management. We can start with WAL, then implement a PM-based index based on current research, then a tuple heap with free space management. Each of the components may be developed and tested independently - Do Ignite internals refactoring to properly abstract storage layer from transactions/communication. Currently, there is an abstraction leak in the storage layer, which makes it aware of particular Ignite implementation details (Binary Objects, partition eviction, etc) - Once the storage is separated, we should be able to plug the new components instead of the "classical" ones WDYT? I believe we should create a detailed IEP with concrete proposals on both PM structures design and Ignite internals changes before making any further code changes. [1] https://openjdk.java.net/jeps/352 [2] https://bugs.openjdk.java.net/browse/JDK-8221397 [3] https://bugs.openjdk.java.net/browse/JDK-8221696 [4] https://github.com/jhalliday/mashona [5] https://www.usenix.org/system/files/conference/fast17/fast17-lee.pdf [6] http://www.vldb.org/pvldb/vol8/p786-chen.pdf [7] https://www.cs.utexas.edu/~vijay/papers/sosp19-recipe.pdf [8] https://cwiki.apache.org/confluence/display/IGNITE/IEP-16%3A+Optimization+of+rebalancing вт, 8 окт. 2019 г. в 08:15, Alexey Goncharuk <alexey.goncha...@gmail.com>: > Igniters, > > I would like to resurrect this discussion and will review the change again > shortly. If anyone want to join the review - you are welcome! > > ср, 22 авг. 2018 г. в 18:49, Denis Magda <dma...@apache.org>: > >> Hi Dmitry, >> >> That's a BSD-3-Clause license if to believe this statement >> "SPDX-License-Identifier: BSD-3-Clause": >> https://github.com/pmem/llpl/blob/master/LICENSE >> >> This license can be used with ASF software: >> https://www.apache.org/legal/resolved.html#category-a >> >> -- >> Denis >> >> On Wed, Aug 22, 2018 at 9:28 AM Dmitriy Pavlov <dpavlov....@gmail.com> >> wrote: >> >> > Hi Denis, >> > >> > Could you please double check if we can refer to any library licensed to >> > Intel. Can we develop code only version of this support (without >> shipping >> > it in release)? >> > >> > https://github.com/apache/ignite/pull/4381 is quite huge change, >> > including 128 files changed, patch review will require resources from >> > community members to review. I would like to be sure we can include this >> > patch from the legal point of view. >> > >> > Sincerely, >> > Dmitriy Pavlov >> > >> > пт, 3 авг. 2018 г. в 19:23, Dmitriy Pavlov <dpavlov....@gmail.com>: >> > >> >> Hi Mulugeta, >> >> >> >> I appologise, I've missed that license is already there. So I guess it >> is >> >> not standard open-source license, it is seems it is not listed in >> >> https://www.apache.org/legal/resolved.html#category-a >> >> >> >> So there can be legal concern related to including this lib as >> dependency >> >> into Apache product. It should not block review, we can later >> >> consult Secretary/Legal to find out how we can correctly include >> reference >> >> to lib. >> >> >> >> Sincerely, >> >> Dmitriy Pavlov >> >> >> >> чт, 2 авг. 2018 г. в 0:24, Mammo, Mulugeta <mulugeta.ma...@intel.com>: >> >> >> >>> Hi Dmitriy, >> >>> >> >>> Do you mean our LLPL library? It has a license, please look here: >> >>> https://github.com/pmem/llpl >> >>> >> >>> Regarding the changes made to Ignite, you may refer to the pull >> request >> >>> here: https://github.com/apache/ignite/pull/4381 >> >>> >> >>> Thanks, >> >>> Mulugeta >> >>> >> >>> -----Original Message----- >> >>> From: Dmitriy Pavlov [mailto:dpavlov....@gmail.com] >> >>> Sent: Wednesday, August 1, 2018 10:49 AM >> >>> To: dev@ignite.apache.org >> >>> Subject: Re: Adding experimental support for Intel Optane DC >> Persistent >> >>> Memory >> >>> >> >>> Hi Mulugeta Mammo, >> >>> >> >>> I've just noticed that repository, what you refer is full fork of >> Ignite. >> >>> How can I see differences with original Ignite? >> >>> >> >>> One more thing, library which you're referencing seems to not contain >> >>> license, at least github can not parse it. Apache product has >> limitations >> >>> which libraries may be used (see >> >>> https://www.apache.org/legal/resolved.html#category-a and >> >>> https://www.apache.org/legal/resolved.html#category-b) >> >>> >> >>> Could you please comment if there is some legal risk? >> >>> >> >>> Sincerely, >> >>> Dmitriy Pavlov >> >>> >> >>> ср, 1 авг. 2018 г. в 20:43, Dmitriy Pavlov <dpavlov....@gmail.com>: >> >>> >> >>> > Hi, >> >>> > >> >>> > This link works for me >> >>> > >> >>> > >> https://cwiki.apache.org/confluence/display/IGNITE/IEP-26%3A+Adding+Ex >> >>> > perimental+Support+for+Intel+Optane+DC+Persistent+Memory >> >>> > >> >>> > Sincerely, >> >>> > Dmitriy Pavlov >> >>> > >> >>> > чт, 26 июл. 2018 г. в 15:31, Stanislav Lukyanov < >> >>> stanlukya...@gmail.com>: >> >>> > >> >>> >> Ah, ok, it’s just the ‘.’ at the end of the link. Removed it and >> it’s >> >>> >> fine. >> >>> >> >> >>> >> From: Stanislav Lukyanov >> >>> >> Sent: 26 июля 2018 г. 15:12 >> >>> >> To: dev@ignite.apache.org >> >>> >> Subject: RE: Adding experimental support for Intel Optane DC >> >>> >> Persistent Memory >> >>> >> >> >>> >> Hi, >> >>> >> >> >>> >> The link you’ve shared gives me 404. >> >>> >> Perhaps you need to add a permission for everyone to access the >> page? >> >>> >> >> >>> >> Thanks, >> >>> >> Stan >> >>> >> >> >>> >> From: Mammo, Mulugeta >> >>> >> Sent: 26 июля 2018 г. 2:44 >> >>> >> To: dev@ignite.apache.org >> >>> >> Subject: Adding experimental support for Intel Optane DC Persistent >> >>> >> Memory >> >>> >> >> >>> >> Hi, >> >>> >> >> >>> >> I have added a new proposal to support Intel Optane DC Persistent >> >>> >> Memory for Ignite here: >> >>> >> >> https://cwiki.apache.org/confluence/display/IGNITE/Adding+Experimenta >> >>> >> l+Support+for+Intel+Optane+DC+Persistent+Memory >> >>> >> . >> >>> >> >> >>> >> I'm looking forward to your feedback and collaboration on this. >> >>> >> >> >>> >> Thanks, >> >>> >> Mulugeta >> >>> >> >> >>> >> >> >>> >> >> >>> >> >> >>> >> >> >> >
