Consistent read what you wrote bucket metadata operations are standard now for S3, Google’s GCS, and anyone who uses Ceph via its radios-gw. I think it will be table stakes for cloud object storage. Although clients will all see the latest metadata state for an object updated in an atomic way, this is not a guarantee regarding views over blob contents. It may be fine but we will have to survey the real semantics of public cloud object stores. We can pick two or three public cloud providers - I would nominate Amazon and Alibaba’s public cloud products - as the design targets for the initial implementation. I like the idea of borrowing from what Hadoop did to define the FileSystem semantics contract and conformance test suite.
I view the current state of things as a starting point not a settled implementation. Hfile tracking cannot be done in meta. Meta is not a scalable place to store state because it cannot be split. Even the minimal state we store there now becomes unwieldy as the number of regions and tables in a cluster grows large. In order to take this into production we require the results of this work to be ultimately committed to branch-2 and made available in new minor release from there. It can’t have a design dependency on something that either doesn’t exist or cannot be released except with a major version increment. We don’t have a path to a releasable branch-2 implementation of a splittable meta table. I hope we can find agreement about this design constraint. > On May 19, 2021, at 8:40 AM, Nick Dimiduk <[email protected]> wrote: > > On Wed, May 19, 2021 at 8:19 AM 张铎(Duo Zhang) <[email protected]> wrote: > >> What about just storing the hfile list in a file? Since now S3 has strong >> consistency, we could safely overwrite a file then I think? >> > > My concern is about portability. S3 isn't the only blob store in town, and > consistent read-what-you-wrote semantics are not a standard feature, as far > as I know. If we want something that can work on 3 or 5 major public cloud > blobstore products as well as a smattering of on-prem technologies, we > should be selective about what features we choose to rely on as > foundational to our implementation. > > Or we are explicitly saying this will only work on S3 and we'll only > support other services when they can achieve this level of compatibility. > > Either way, we should be clear and up-front about what semantics we demand. > Implementing some kind of a test harness that can check compatibility would > help here, a similar effort to that of defining standard behaviors of HDFS > implementations. > > I love this discussion :) > > And since the hfile list file will be very small, renaming will not be a >> big problem. >> > > Would this be a file per store? A file per region? Ah. Below you imply it's > per store. > > Wellington Chevreuil <[email protected]> 于2021年5月19日周三 >> 下午10:43写道： >> >>> Thank you, Andrew and Duo, >>> >>> Talking internally with Josh Elser, initial idea was to rebase the >> feature >>> branch with master (in order to catch with latest commits), then focus on >>> work to have a minimal functioning hbase, in other words, together with >> the >>> already committed work from HBASE-25391, make sure flush, compactions, >>> splits and merges all can take advantage of the persistent store file >>> manager and complete with no need to rely on renames. These all map to >> the >>> substasks HBASE-25391, HBASE-25392 and HBASE-25393. Once we could test >> and >>> validate this works well for our goals, we can then focus on snapshots, >>> bulkloading and tooling. >>> >>> S3 now supports strong consistency, and I heard that they are also >>>> implementing atomic renaming currently, so maybe that's one of the >>> reasons >>>> why the development is silent now.. >>>> >>> Interesting, I had no idea this was being implemented. I know, however, a >>> version of this feature is already available on latest EMR releases (at >>> least from 6.2.0), and AWS team has published their own blog post with >>> their results: >>> >>> >> https://aws.amazon.com/blogs/big-data/amazon-emr-6-2-0-adds-persistent-hfile-tracking-to-improve-performance-with-hbase-on-amazon-s3/ >>> >>> But I do not think store hfile list in meta is the only solution. It will >>>> cause cyclic dependencies for hbase:meta, and then force us a have a >>>> fallback solution which makes the code a bit ugly. We should try to see >>> if >>>> this could be done with only the FileSystem. >>>> >>> This is indeed a relevant concern. One idea I had mentioned in the >> original >>> design doc was to track committed/non-committed files through xattr (or >>> tags), which may have its own performance issues as explained by Stephen >>> Wu, but is something that could be attempted. >>> >>> Em qua., 19 de mai. de 2021 às 04:56, 张铎(Duo Zhang) < >> [email protected] >>>> >>> escreveu: >>> >>>> S3 now supports strong consistency, and I heard that they are also >>>> implementing atomic renaming currently, so maybe that's one of the >>> reasons >>>> why the development is silent now... >>>> >>>> For me, I also think deploying hbase on cloud storage is the future, >> so I >>>> would also like to participate here. >>>> >>>> But I do not think store hfile list in meta is the only solution. It >> will >>>> cause cyclic dependencies for hbase:meta, and then force us a have a >>>> fallback solution which makes the code a bit ugly. We should try to see >>> if >>>> this could be done with only the FileSystem. >>>> >>>> Thanks. >>>> >>>> Andrew Purtell <[email protected]> 于2021年5月19日周三 上午8:04写道： >>>> >>>>> Wellington (and et. al), >>>>> >>>>> S3 is also an important piece of our future production plans. >>>>> Unfortunately, we were unable to assist much with last year's work, >> on >>>>> account of being sidetracked by more immediate concerns. Fortunately, >>>> this >>>>> renewed interest is timely in that we have an HBase 2 project where, >> if >>>>> this can land in a 2.5 or a 2.6, it could be an important cost to >> serve >>>>> optimization, and one we could and would make use of. Therefore I >> would >>>>> like to restate my employer's interest in this work too. It may just >> be >>>>> Viraj and myself in the early days. >>>>> >>>>> I'm not sure how best to collaborate. We could review changes from >> the >>>>> original authors, new changes, and/or divide up the development >> tasks. >>> We >>>>> can certainly offer our time for testing, and can afford the costs of >>>>> testing against the S3 service. >>>>> >>>>> >>>>> On Tue, May 18, 2021 at 12:16 PM Wellington Chevreuil < >>>>> [email protected]> wrote: >>>>> >>>>>> Greetings everyone, >>>>>> >>>>>> HBASE-24749 has been proposed almost a year ago, introducing a new >>>>>> StoreFile tracker as a way to allow for any hbase hfile >> modifications >>>> to >>>>> be >>>>>> safely completed without needing a file system rename. This seems >>>> pretty >>>>>> relevant for deployments over S3 file systems, where rename >>> operations >>>>> are >>>>>> not atomic and can have a performance degradation when multiple >>>> requests >>>>>> get concurrently submitted to the same bucket. We had done >>> superficial >>>>>> tests and ycsb runs, where individual renames of files larger than >>> 5GB >>>>> can >>>>>> take a few hundreds of seconds to complete. We also observed >> impacts >>> in >>>>>> write loads throughput, the bottleneck potentially being the >> renames. >>>>>> >>>>>> With S3 being an important piece of my employer cloud solution, we >>>> would >>>>>> like to help it move forward. We plan to contribute new patches per >>> the >>>>>> original design/Jira, but we’d also be happy to review changes from >>> the >>>>>> original authors, too. Please let us know if anyone has any >> concerns, >>>>>> otherwise we’ll start to self-assign issues on HBASE-24749 >>>>>> >>>>>> Wellington >>>>>> >>>>> >>>>> >>>>> -- >>>>> Best regards, >>>>> Andrew >>>>> >>>>> Words like orphans lost among the crosstalk, meaning torn from >> truth's >>>>> decrepit hands >>>>> - A23, Crosstalk >>>>> >>>> >>> >>
