Great points. Thanks fellas!
Andrew Purtell wrote:
Right, these drawbacks are what I was getting at with "impose limits on
how HBase structures storage on the filesystem". It does imply major
changes to filesystem structure and multiple WALs. I didn't think of
snapshots, you are right that makes filesystem reorganization more
complicated. To your earlier point I think soft quotas are a fine start as
well.
On Wed, Nov 2, 2016 at 3:28 PM, Enis Söztutar<enis....@gmail.com> wrote:
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)
