Thanks Andrew, I forgot to mention that we have considered using the HDFS quota enforcement directly as well, but decided against it for a couple of reasons. - Our current layout has files in the data directory, as well as archive directory and WALs, etc. Since there is no option for HDFS quotas to span multiple directories, we can only use the HDFS quotas for main data files, and not snapshots, etc unless we do major surgery in our file layouts. This will get more complicated if we want to do flat layout, etc later on. - Since WALs would not be in any namespace unless we do wal-per-namespace, that means that once a single NS's HDFS quota is reached, it might affect everybody else and potentially cause havoc on the cluster. The problem would be that if a single NS is out of space, we cannot perform flushes at all. This would cause the WALs to be backed up and kept forever and affect all of the other regions from different tables / namespaces causing unavailability for unrelated tables. Wal-per-namespace also has to be implemented and WALs be moved under a shared NS directory to share the data and WAL requiring further layout changes. It also will not be optimal if there is a large number of namespaces. - Will only work with HDFS, while HBase can use other file systems.
Enis On Wed, Nov 2, 2016 at 3:01 PM, Andrew Purtell <apurt...@apache.org> wrote: > Another approach to hard limits could be pushing the quota down to the HDFS > level, because HDFS would have a very accurate assessment of quota > utilization at all times, but this would only work with HDFS and impose > limits on how HBase structures storage on the filesystem (e.g. all files > for a namespace must be under a common root). Still, implementation would > be "easy": over hard quota, all allocations would fail, the bulk of the > effort is hardening response to allocation failures. > > On Wed, Nov 2, 2016 at 1:11 PM, Enis Söztutar <e...@apache.org> wrote: > > > Thanks Josh for the doc and pursuing this. > > > > I was involved with some of the design choices so consider me a +1 on the > > general approach. One topic which is not covered here is that the other > > design decision that we could have pursued is a more strict control on > the > > quota usage so that we would always guarantee that the namespace / table > > cannot use more than allocated disk space. This hard-limit approach would > > differ from the proposed "soft-limit" approach because the soft limit > > approach can end up overusing the disk space by a small amount (because > it > > takes time to detect the quota limit is reached and enforcing of the > > limit). > > > > The hard-limit approach maybe built by doing a lease kind of mechanism > > where the master gives away disk space leases to region servers from the > > remaining limit, and the regionservers make sure that they cannot > allocate > > more space than the lease dictates. By ensuring that the space is > > pre-allocated via leases, we can always make sure that strict limits are > > applied. Though, this approach would be harder to build and stabilize > > because it will need new mechanisms for distributing and managing this > kind > > of leases as well as tuning the allocations to make sure that > regionservers > > never block flushes or compactions due to lack of lease in time would > prove > > challenging to get it right. > > > > We generally think that the "soft-limit" approach would be a good enough > > approximation and the error bounds on over-allocation would be minimal > and > > negligible in production. Thus, the proposal is to implement the soft > > approach with good documentation about how much space can be > over-allocated > > in a worst-case scenario. > > > > Enis > > > > On Wed, Nov 2, 2016 at 12:15 PM, Josh Elser <els...@apache.org> wrote: > > > > > Thanks for the reviews so far, Ted and Stack. The comments were great > and > > > much appreciated. > > > > > > Interpreting consensus from lack of objection, I'm going to move ahead > in > > > earnest starting to work on what was described in the doc. Expect to > see > > > some work break-out happening under HBASE-16961 and patches starting to > > > land. > > > > > > I'm also happy to entertain more discussion if anyone hasn't found the > > > time to read/comment yet. > > > > > > Thanks! > > > > > > - Josh > > > > > > > > > Josh Elser wrote: > > > > > >> Sure thing, Ted. > > >> > > >> https://docs.google.com/document/d/1VtLWDkB2tpwc_zgCNPE1ulZO > > >> eecF-YA2FYSK3TSs_bw/edit?usp=sharing > > >> > > >> > > >> Let me open an umbrella issue for now. I can break up the work later. > > >> > > >> https://issues.apache.org/jira/browse/HBASE-16961 > > >> > > >> Ted Yu wrote: > > >> > > >>> Josh: > > >>> Can you put the doc in google doc so that people can comment on it ? > > >>> > > >>> Is there a JIRA opened for this work ? > > >>> Please open one if there is none. > > >>> > > >>> Thanks > > >>> > > >>> On Fri, Oct 28, 2016 at 9:00 AM, Josh Elser<els...@apache.org> > wrote: > > >>> > > >>> Hi folks, > > >>>> > > >>>> I'd like to propose the introduction of FileSystem quotas to HBase. > > >>>> > > >>>> Here's a design doc[1] available which (hopefully) covers all of the > > >>>> salient points of what I think an initial version of such a feature > > >>>> would > > >>>> include. > > >>>> > > >>>> tl;dr We can define quotas on tables and namespaces. Region size is > > >>>> computed by RegionServers and sent to the Master. The Master > inspects > > >>>> the > > >>>> sizes of Regions, rolling up to table and namespace sizes. Defined > > >>>> quotas > > >>>> in the quota table are evaluated given the computed sizes, and, for > > >>>> those > > >>>> tables/namespaces violating the quota, RegionServers are informed to > > >>>> take > > >>>> some action to limit any further filesystem growth by that > > >>>> table/namespace. > > >>>> > > >>>> I'd encourage you to give the document a read -- I tried to cover as > > >>>> much > > >>>> as I could without getting unnecessarily bogged down in > implementation > > >>>> details. > > >>>> > > >>>> Feedback is, of course, welcomed. I'd like to start sketching out a > > >>>> breakdown of the work (all writing and no programming makes Josh a > sad > > >>>> boy). I'm happy to field any/all questions. Thanks in advance. > > >>>> > > >>>> - Josh > > >>>> > > >>>> [1] http://home.apache.org/~elserj/hbase/FileSystemQuotasforApac > > >>>> heHBase.pdf > > >>>> > > >>>> > > >>> > > > > > > -- > Best regards, > > - Andy > > Problems worthy of attack prove their worth by hitting back. - Piet Hein > (via Tom White) >
