This thread talks of “durability” via filesystem characteristics but also for single system quick Start type deployments. For durability we need multi server deployments. No amount of hacking a single system deployment is going to give us durability as users will expect (“don’t lose my data”). I believe my comments are on topic.
> On Apr 15, 2020, at 11:03 AM, Nick Dimiduk <ndimi...@apache.org> wrote: > > On Wed, Apr 15, 2020 at 10:28 AM Andrew Purtell <apurt...@apache.org> wrote: > >> Nick's mail doesn't make a distinction between avoiding data loss via >> typical tmp cleaner configurations, unfortunately adjacent to mention of >> "durability", and real data durability, which implies more than what a >> single system configuration can offer, no matter how many tweaks we make to >> LocalFileSystem. Maybe I'm being pedantic but this is something to be >> really clear about IMHO. >> > > I prefer to focus the attention of this thread to the question of data > durability via `FileSystem` characteristics. I agree that there are > concerns of durability (and others) around the use of the path under /tmp. > Let's keep that discussion in the other thread. > >> On Wed, Apr 15, 2020 at 10:05 AM Sean Busbey <bus...@apache.org> wrote: >> >>> I think the first assumption no longer holds. Especially with the move >>> to flexible compute environments I regularly get asked by folks what >>> the smallest HBase they can start with for production. I can keep >>> saying 3/5/7 nodes or whatever but I guarantee there are folks who >>> want to and will run HBase with a single node. Probably those >>> deployments won't want to have the distributed flag set. None of them >>> really have a good option for where the WALs go, and failing loud when >>> they try to go to LocalFileSystem is the best option I've seen so far >>> to make sure folks realize they are getting into muddy waters. >>> >>> I agree with the second assumption. Our quickstart in general is too >>> complicated. Maybe if we include big warnings in the guide itself, we >>> could make a quickstart specific artifact to download that has the >>> unsafe disabling config in place? >>> >>> Last fall I toyed with the idea of adding an "hbase-local" module to >>> the hbase-filesystem repo that could start us out with some >>> optimizations for single node set ups. We could start with a fork of >>> RawLocalFileSystem (which will call OutputStream flush operations in >>> response to hflush/hsync) that properly advertises its >>> StreamCapabilities to say that it supports the operations we need. >>> Alternatively we could make our own implementation of FileSystem that >>> uses NIO stuff. Either of these approaches would solve both problems. >>> >>> On Wed, Apr 15, 2020 at 11:40 AM Nick Dimiduk <ndimi...@apache.org> >> wrote: >>>> >>>> Hi folks, >>>> >>>> I'd like to bring up the topic of the experience of new users as it >>>> pertains to use of the `LocalFileSystem` and its associated (lack of) >>> data >>>> durability guarantees. By default, an unconfigured HBase runs with its >>> root >>>> directory on a `file:///` path. This patch is picked up as an instance >> of >>>> `LocalFileSystem`. Hadoop has long offered this class, but it has never >>>> supported `hsync` or `hflush` stream characteristics. Thus, when HBase >>> runs >>>> on this configuration, it is unable to ensure that WAL writes are >>> durable, >>>> and thus will ACK a write without this assurance. This is the case, >> even >>>> when running in a fully durable WAL mode. >>>> >>>> This impacts a new user, someone kicking the tires on HBase following >> our >>>> Getting Started docs. On Hadoop 2.8 and before, an unconfigured HBase >>> will >>>> WARN and cary on. Hadoop 2.10+, HBase will refuse to start. The book >>>> describes a process of disabling enforcement of stream capability >>>> enforcement as a first step. This is a mandatory configuration for >>> running >>>> HBase directly out of our binary distribution. >>>> >>>> HBASE-24086 restores the behavior on Hadoop 2.10+ to that of running on >>>> 2.8: log a warning and cary on. The critique of this approach is that >>> it's >>>> far too subtle, too quiet for a system operating in a state known to >> not >>>> provide data durability. >>>> >>>> I have two assumptions/concerns around the state of things, which >>> prompted >>>> my solution on HBASE-24086 and the associated doc update on >> HBASE-24106. >>>> >>>> 1. No one should be running a production system on `LocalFileSystem`. >>>> >>>> The initial implementation checked both for `LocalFileSystem` and >>>> `hbase.cluster.distributed`. When running on the former and the latter >> is >>>> false, we assume the user is running a non-production deployment and >>> carry >>>> on with the warning. When the latter is true, we assume the user >>> intended a >>>> production deployment and the process terminates due to stream >> capability >>>> enforcement. Subsequent code review resulted in skipping the >>>> `hbase.cluster.distributed` check and simply warning, as was done on >> 2.8 >>>> and earlier. >>>> >>>> (As I understand it, we've long used the `hbase.cluster.distributed` >>>> configuration to decide if the user intends this runtime to be a >>> production >>>> deployment or not.) >>>> >>>> Is this a faulty assumption? Is there a use-case we support where we >>>> condone running production deployment on the non-durable >>> `LocalFileSystem`? >>>> >>>> 2. The Quick Start experience should require no configuration at all. >>>> >>>> Our stack is difficult enough to run in a fully durable production >>>> environment. We should make it a priority to ensure it's as easy as >>>> possible to try out HBase. Forcing a user to make decisions about data >>>> durability before they even launch the web ui is a terrible experience, >>> in >>>> my opinion, and should be a non-starter for us as a project. >>>> >>>> (In my opinion, the need to configure either `hbase.rootdir` or >>>> `hbase.tmp.dir` away from `/tmp` is equally bad for a Getting Started >>>> experience. It is a second, more subtle question of data durability >> that >>> we >>>> should avoid out of the box. But I'm happy to leave that for another >>>> thread.) >>>> >>>> Thank you for your time, >>>> Nick >>> >> >> >> -- >> Best regards, >> Andrew >> >> Words like orphans lost among the crosstalk, meaning torn from truth's >> decrepit hands >> - A23, Crosstalk >>
