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https://issues.apache.org/jira/browse/HBASE-22149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16826393#comment-16826393
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Sean Mackrory commented on HBASE-22149:
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Added some contract tests I had missed that get a lot more coverage, fixed all
the issues I was having in the tests (it was just tests stepping on each
other's paths because they weren't all in separate directories and are supposed
to be), am now normalizing all paths and sorting arrays in one central place.
When I normalize paths for locking, I'm doing /scheme/hostname/path to ensure
using this for multiple filesystems is safe.
Some minor to do's left, but they definitely don't impact my test cases or the
HBase workloads that have run on this so far:
- mkdirs has implications for any parent directories that don't exist yet,
although it will only lock the path. I can't think of a scenario where this
would cause a problem, though.
- The local lock implementation isn't re-entrant if you read-lock a path and
then try to read-lock a parent in the same thread. I don't think anyone would
use it in production, and the ZK implementation is the default even for the
unit tests. This implementation is really only still there in case it helps
with debugging other logic.
- The whole thing really depends on Hadoop 3+ (in production, S3Guard is
required and isn't in the Hadoop 2 releases, and even just for testing there's
a lot of changes required to get it to compile). I'm wondering if there's an
easy way to only include this module only with the Hadoop 3 profile. I haven't
seen one, so... hints welcome :)
Other than that: what else would the community like to see before this was
committed (albeit perhaps with a big "experimental" label until this has gone
through more scale and integration testing).
> HBOSS: A FileSystem implementation to provide HBase's required semantics
> ------------------------------------------------------------------------
>
> Key: HBASE-22149
> URL: https://issues.apache.org/jira/browse/HBASE-22149
> Project: HBase
> Issue Type: New Feature
> Components: Filesystem Integration
> Reporter: Sean Mackrory
> Assignee: Sean Mackrory
> Priority: Critical
> Attachments: HBASE-22149-hadoop.patch, HBASE-22149-hbase-2.patch,
> HBASE-22149-hbase-3.patch, HBASE-22149-hbase-4.patch,
> HBASE-22149-hbase-5.patch, HBASE-22149-hbase.patch
>
>
> (Have been using the name HBOSS for HBase / Object Store Semantics)
> I've had some thoughts about how to solve the problem of running HBase on
> object stores. There has been some thought in the past about adding the
> required semantics to S3Guard, but I have some concerns about that. First,
> it's mixing complicated solutions to different problems (bridging the gap
> between a flat namespace and a hierarchical namespace vs. solving
> inconsistency). Second, it's S3-specific, whereas other objects stores could
> use virtually identical solutions. And third, we can't do things like atomic
> renames in a true sense. There would have to be some trade-offs specific to
> HBase's needs and it's better if we can solve that in an HBase-specific
> module without mixing all that logic in with the rest of S3A.
> Ideas to solve this above the FileSystem layer have been proposed and
> considered (HBASE-20431, for one), and maybe that's the right way forward
> long-term, but it certainly seems to be a hard problem and hasn't been done
> yet. But I don't know enough of all the internal considerations to make much
> of a judgment on that myself.
> I propose a FileSystem implementation that wraps another FileSystem instance
> and provides locking of FileSystem operations to ensure correct semantics.
> Locking could quite possibly be done on the same ZooKeeper ensemble as an
> HBase cluster already uses (I'm sure there are some performance
> considerations here that deserve more attention). I've put together a
> proof-of-concept on which I've tested some aspects of atomic renames and
> atomic file creates. Both of these tests fail reliably on a naked s3a
> instance. I've also done a small YCSB run against a small cluster to sanity
> check other functionality and was successful. I will post the patch, and my
> laundry list of things that still need work. The WAL is still placed on HDFS,
> but the HBase root directory is otherwise on S3.
> Note that my prototype is built on Hadoop's source tree right now. That's
> purely for my convenience in putting it together quickly, as that's where I
> mostly work. I actually think long-term, if this is accepted as a good
> solution, it makes sense to live in HBase (or it's own repository). It only
> depends on stable, public APIs in Hadoop and is targeted entirely at HBase's
> needs, so it should be able to iterate on the HBase community's terms alone.
> Another idea [~ste...@apache.org] proposed to me is that of an inode-based
> FileSystem that keeps hierarchical metadata in a more appropriate store that
> would allow the required transactions (maybe a special table in HBase could
> provide that store itself for other tables), and stores the underlying files
> with unique identifiers on S3. This allows renames to actually become fast
> instead of just large atomic operations. It does however place a strong
> dependency on the metadata store. I have not explored this idea much. My
> current proof-of-concept has been pleasantly simple, so I think it's the
> right solution unless it proves unable to provide the required performance
> characteristics.
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