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From Noah Slater <nsla...@apache.org>
Subject Re: [VOTE] Merge BigCouch
Date Wed, 15 May 2013 14:03:08 GMT
PARTY TIME 🎉


On 15 May 2013 10:40, Robert Newson <rnewson@apache.org> wrote:

> Thanks everyone.
>
> The tally is;
>
> 13 +1's
>
> The vote passes. We'll now move on to IP clearance. Once that's done
> the work will arrive on a feature branch in our main git repository.
>
> B.
>
>
> On 13 May 2013 04:31, Jason Smith <jhs@iriscouch.com> wrote:
> > Sorry, just catching up.
> >
> > +1
> >
> > On Fri, May 10, 2013 at 4:29 PM, Jan Lehnardt <jan@apache.org> wrote:
> >> +1
> >>
> >> Jan
> >> --
> >>
> >> On May 7, 2013, at 21:34 , Robert Newson <rnewson@apache.org> wrote:
> >>
> >>> Hi All,
> >>>
> >>> I propose to merge in the following work,
> >>> https://github.com/rnewson/couchdb/tree/nebraska-merge-candidate to
> >>> the official Apache CouchDB repository to a new branch (i.e, *not*
> >>> master). Once there, the full CouchDB developer community can begin
> >>> the work to incorporate the code here into an official release.
> >>>
> >>> You do not need to respond if you are in agreement. If there is no
> >>> response in 72 hours, I will assume lazy consensus. If we reach
> >>> consensus, I will start the IP clearance process and then the merge.
> >>>
> >>> As most of you know, Paul Davis and I recently sequestered ourselves
> >>> away from society (in a place called Nebraska) to make this merge
> >>> happen. I want to clarify that this work is not the BigCouch code you
> >>> can see on github.com/cloudant/bigcouch but the Cloudant platform from
> >>> which BigCouch was made. This means it is bang up to date with all the
> >>> bug fixes and feature enhancements we've made in the last eighteen
> >>> months or more. With that clarification made, here are our notes about
> >>> what we achieved, what it means to the project and what isn't yet
> >>> done;
> >>>
> >>> Nebraska Merge Roundup
> >>>
> >>>
> >>> Stats:
> >>>
> >>>
> >>> 1402 - total new commits
> >>>
> >>> 312 - commits written during the merge (will be reduced substantially
> >>> by squashing)
> >>>
> >>> 408 - number of files changed
> >>>
> >>> 21,897 - number of lines added
> >>>
> >>> 4,277 - number of lines removed
> >>>
> >>> A retrospective:
> >>>
> >>> Bob Newson and I have come to the end of our merge sprint on getting
> >>> BigCouch merged into Apache CouchDB. Its been a productive ten days
> >>> here in the midwest. I managed to get Bob out to a bowling alley and
> >>> he managed to get me to a sushi restaurant. In between the cultural
> >>> exchanges we’ve also managed to get a significant amount of work done
> >>> on the merging as well.
> >>>
> >>>
> >>> The current status of the merge is that we’ve managed to resolve the
> >>> differences in the single node execution of CouchDB. Both the
> >>> JavaScript and Erlang test suites run with only one failure in the
> >>> Erlang test suite due to a (deliberately) missing constraint on the
> >>> number of operating system processes. This should be a relatively
> >>> straightforward fix but was not prioritized during our limited time to
> >>> work on the larger issues.
> >>>
> >>>
> >>> We merged a large number of performance and stability enhancements
> >>> back into single node CouchDB as well as a number of pure bug fixes.
> >>> The biggest highlight is a brand new compactor that is both faster and
> >>> creates smaller and better organized post-compaction databases.
> >>>
> >>>
> >>> The current status of the merge is that single node operations should
> >>> be completely unaffected as demonstrated by the test suite passing. On
> >>> the other hand we haven’t yet finished getting the clustered code
> >>> merged to use some of the new changes in single node CouchDB. The
> >>> single most significant portion of this work involves updates to the
> >>> internal cluster API for views to use the recently rewritten indexer
> >>> APIs. This should be a relatively straightforward bit of work that
> >>> we’ll be finishing over the next few weeks.
> >>>
> >>>
> >>> All in all the merge work done so far has been quite successful. We’ve
> >>> met our primary goal of getting the code merged in a fashion that does
> >>> not affect single node operation while providing a starting point for
> >>> the larger community to start reviewing the more significant changes
> >>> made. Given the size of the diff between the two code bases we never
> >>> expected to have a fully working clustered solution after ten days of
> >>> work but we have succeeded in providing a base of work that will allow
> >>> us and new contributors to get up to speed quickly.
> >>>
> >>>
> >>> This work, coupled with work by Dave Cottlehuber and Benoît Chesneau
> >>> on updating the build system and various other internal updates, will
> >>> provide a solid foundation for work going forward. Its an exciting
> >>> time for CouchDB and anyone interested should keep an eye on the next
> >>> few releases as we ramp up work on various core aspects of the
> >>> database.
> >>>
> >>>
> >>> We’ve had an exciting few days working to prepare the road for an
> >>> exciting next twelve to eighteen months. We hope that everyone will
> >>> feel as excited as we do about the next twelve to eighteen months for
> >>> Apache CouchDB. It should be an exciting ride.
> >>>
> >>>
> >>>
> >>> Things we got done
> >>>
> >>>
> >>> * Large update to the source tree layout for Erlang applications. Each
> >>> application now has a src/appname/(c_src|ebin|priv|src) structure. The
> >>> build system has been updated.
> >>>
> >>> * Renamed src/couchdb to src/couch to match the Erlang convention of
> >>> the top directory name matching the Erlang application name.
> >>>
> >>> * Imported Cloudant Erlang applications for clustered CouchDB. These
> >>> are imported with their history by using git subtree and merging the
> >>> top level commit. These are not external deps, development will happen
> >>> within the CouchDB tree. The imported apps are:
> >>>
> >>>
> >>>   * config - A couch_config replacement (Behavior is mostly identical
> >>> to couch_config except how we listen for configuration changes
> >>> internally to allow for smooth hot code upgrade).
> >>>
> >>>   * twig - An rsyslog source replacement for couch_log.
> >>>
> >>>   * rexi - An RPC library. Replaces Erlang’s built-in rex application
> >>> to avoid costly safety measures in the interest of performance and
> >>> throughput.
> >>>
> >>>   * mem3 - The “Dynamo” part of BigCouch responsible for managing
> cluster state
> >>>
> >>>   * fabric - The internal cluster-aware CouachDB API
> >>>
> >>>   * ets_lru - A small library application that provides an LRU
> >>> implementation using a couple ets tables.
> >>>
> >>>   * ddoc_cache - Caches design documents on each node for use in
> >>> design handler functions. This uses an ets_lru cache with a very short
> >>> TTL.
> >>>
> >>>   * chttpd - The cluster aware HTTP layer
> >>>
> >>>
> >>> Each imported app also had its build system updated to use Autotools
> >>> along with the necessary updates noted above for the new application
> >>> layouts for existing CouchDB erlang apps.
> >>>
> >>>
> >>> * Merged a large amount of updates and fixes to couch_replicator based
> >>> on work done internally at Cloudant. Unfortunately due to an error
> >>> when we created our internal clone we lost a bit of history in some of
> >>> the initial merge and have a big commit that affects
> >>> couch_replicator_manager mostly. There are a number of other commits
> >>> related to couch_replicator that resolve the single node vs. clustered
> >>> differences. Some noticeable couch_replicator features:
> >>>
> >>>
> >>>   * Optionally disable checkpoints so that replication can work when
> >>> a source is read only. This should only be used for smaller databases
> >>> as each replication call has to scan the entire source database on
> >>> each invocation.
> >>>
> >>>   * A new changes_pending field in the _active_tasks output
> >>>
> >>>   * A fix to the continuous replication to automatically reconnect to
> >>> a continuous changes feed when it sees a last_seq value. This allows
> >>> for the source to selectively recycle the HTTP connections used which
> >>> can be quite useful for “permanent” replications.
> >>>
> >>>   * A multitude of smaller bug fix and stability enhancements.
> >>>
> >>>
> >>> Updates to single node couch:
> >>>
> >>>
> >>> * We changed the by_seq tree to store a copy of the #full_doc_info{}
> >>> record instead of the #doc_info{} record. This gives significant speed
> >>> improvements for compaction and replication and generally anything
> >>> that needs to walk the by_seq tree and access document bodies
> >>> internally.
> >>>
> >>> * We rewrote the compactor to be significantly faster as well as
> >>> provides significantly better compacted databases. The two main halves
> >>> are to use a temp file and replace the use of btrees in the temp file.
> >>> The temp file only contains a temporary copy of the document ids. At
> >>> the end of a compaction run we then rebuild the by_id btree in the
> >>> compaction file from this temp file. The reason this helps so much is
> >>> that the compaction is based on the update_seq btree, which for most
> >>> cases means that the id tree is updated in roughly random order which
> >>> is very bad for our append only btrees. By using the tmp file we can
> >>> stream it in order back into the compacted db file at the end of
> >>> compacting, generating a minimum amount of garbage in the process. The
> >>> other upgrade was to implement an external merge sort module
> >>> (couch_emsort) that is used with this temporary file.
> >>>
> >>> * Reject updates to design docs that introduce updates that break
> >>> compilation for source code. Currently we only check map and reduce
> >>> calls as the other should provide user visible errors instead of
> >>> inexplicably empty views.
> >>>
> >>> because my OCD kicked in and I was unable to resist.
> >>>
> >>> * Reverted a change made a long time ago that uses two file
> >>> descriptors for each database. See the todo list.
> >>>
> >>> * The reason to remove the second fd is so that we can rewrite ref
> >>> counting. Better ref counting makes everyone happy, but the real
> >>> reason is for this next bullet point:
> >>>
> >>> * Optimize couch_server to not require a round trip message pass for
> >>> opening a database that’s in the LRU. This is a significant
> >>> performance boost for high concurrency access. We also optimized
> >>> couch_server internals to not blow up when it’s under load.
> >>>
> >>> * Introduce a #leaf{} record into the revision trees. This is never
> >>> written to disk but makes internal code a lot cleaner when dealing
> >>> with multiple versions of rev tree values.
> >>>
> >>> * Some changes to couch_changes to enable clustered access. Also some
> >>> general cleanup
> >>>
> >>> * Internal changes to how CouchDB is booted in Erlang land. Not very
> >>> sexy but this removes a lot of complicated un-Erlangy bits. We still
> >>> have a bit of work left here.
> >>>
> >>> * btree chunk sizes are now configurable which can allow people to
> >>> adjust the RAM/speed tradeoffs a bit more.
> >>>
> >>> * We now load update validation functions on the first write. This is
> >>> a cluster-motivated change because the clustered version of this call
> >>> is expensive and can lead to race conditions when opening a bunch of
> >>> db shards simultaneously. This should be invisible to external
> >>> clients.
> >>>
> >>> * Disabled conflict detection for local docs. They don’t replicate so
> >>> there’s no point. This just led to clusters getting stuck and confused
> >>> when there were lots of replications happening.
> >>>
> >>> * Changes to the multipart/mime parsing code. Necessary for clustered
> >>> attachment uploads to split the incoming data  stream into N copies.
> >>>
> >>> * Don’t use init:restart/0 when reloading the ICU driver. I think
> >>> this has a bug. But we should rewrite this driver to be a NIF anyway.
> >>>
> >>> * New couch OS process manager. Significantly faster access to OS
> >>> processes under heavy load. This replaces the hard limit with a soft
> >>> limit. Process spawned over the soft limit will be used until they’ve
> >>> sat idle for a few minutes and then be closed. We have a todo item to
> >>> add the hard ceiling back in (while keeping the soft ceiling).
> >>>
> >>> * Automatically replace some easily identifiable JS reductions with
> >>> their builtin counterparts. Uses a regex to do the detection so its
> >>> not too smart.
> >>>
> >>> * Improved view updater write batch.
> >>>
> >>> * Updates to couchjs’ views.js to improve index update speeds
> >>>
> >>> * Updates to the _stats bultin reduce to allow reduces to work over
> >>> emitted stats objects. Sometimes clients have summary data in a doc,
> >>> and this allows them to combine stats if they follow the same pattern
> >>> as the builtin expects.
> >>>
> >>> * Added a config:reload() that is accessible by POST’ing to
> >>> _config/_reload. Used by the JS tests to reset the config to what's on
> >>> disk. This should prevent those test run failures where a test fails
> >>> leaving the config in a bad state causing all subsequent tests to
> >>> fail. I think. Maybe.
> >>>
> >>> * Databases are deleted synchronously in the test suite. We may need
> >>> to address this on Windows. But it does seem to reduce the number of
> >>> “{error, file_exists}” failures.
> >>>
> >>> * I reimplemented the JS restartServer() function. There’s a new
> >>> _restart/token URL that will given a unique value for each instance of
> >>> the Erlang VM. To run a restart we grab the current token value, hit
> >>> _restart, then wait till we get a successful response with a different
> >>> token. This appears to have made the restart strategy more robust.
> >>>
> >>>
> >>>
> >>> Things that need doing
> >>>
> >>>
> >>> IP Clearance -
> >>>
> >>>
> >>> We’ll need to track down if we have the CCLA as well as look at each
> >>> source file added to make sure each one is strictly from Cloudant or
> >>> has an amenable license. I’m pretty sure that the only one of interest
> >>> is trunc_io.erl but we need to be thorough.
> >>>
> >>> documentation -
> >>>
> >>>
> >>> There shouldn’t be much here since the entire point of this merge was
> >>> to not change the visible behavior of single node couch. A few things
> >>> to add about the testing endpoints. Maybe an update to the compaction
> >>> section mention the two new file names used.
> >>>
> >>>
> >>> Copyright notices -
> >>>
> >>>
> >>> We need to strip out copyright notices from individual files and make
> >>> sure all files have a standard Apache License v2 header.
> >>>
> >>>
> >>> clustered vhosts -
> >>>
> >>>
> >>> We’ve never implemented this at Cloudant. We either need to write a
> >>> cluster or go back and tell people to use HAProxy (or similar) for
> >>> such things.
> >>>
> >>>
> >>> twig -
> >>>
> >>>
> >>> We need to add another output type to twig that is configurable in
> >>> some manner. Right now we spit out entire rsyslog records which isn’t
> >>> useful for most people. We’ll need to implement the file writer from
> >>> couch_log as well as update the _log HTTP handler to know when it can
> >>> and can’t expect to find data on disk.
> >>>
> >>>
> >>> fabric -
> >>>
> >>>
> >>> This is going to need a lot of work. Specifically view access is going
> >>> to need to be updated to work with couch_mrview and friends.
> >>>
> >>>
> >>> Boot a dev cluster -
> >>>
> >>>
> >>> Once we fix up the clustering code we’ll need to write instructions
> >>> and scripts for pulling up a dev cluster.
> >>>
> >>>
> >>> OTP stuff -
> >>>
> >>>
> >>> We’ve updated each app but we still need to pull some parts out of
> >>> couchdb into their own application. Specifically the HTTP layer needs
> >>> its own app. We could probably pull out the os process/query_servers
> >>> as well as the os daemons and friends. Once done we need to update the
> >>> supervision trees so we don’t have things like couch starting and
> >>> managing the replication manager process.
> >>>
> >>>
> >>> ddoc_cache -
> >>>
> >>>
> >>> Wire this up in couch_httpd_db to actually be used. Right now its only
> >>> used in chttpd.
> >>>
> >>>
> >>> couch_file upgrade -
> >>>
> >>>
> >>> The revert to remove the second updater_fd from each #db{} record
> >>> means that we’re back in the original position of files appearing to
> >>> slow down significantly under load. Since the initial hammer approach
> >>> of just adding a second fd we’ve since discovered that the underlying
> >>> bug is due to the way that message passing works combined with
> >>> Erlang’s file io. Significantly though is the fact that the fix is
> >>> rather simple to implement. A first draft of this work is on an old
> >>> branch of mine here:
> >>>
> >>>
> >>>   https://github.com/davisp/couchdb/commit/d856878
> >>>
> >>>
> >>> finish the size calculating changes -
> >>>
> >>>
> >>> The #leaf{} record change is to enable us to add more data size
> >>> calculations. CouchDB master calculates a data size that account for
> >>> all bytes that are active in a .couch file. Cloudant is interested in
> >>> the total size of uncompressed docs and attachments minus the internal
> >>> overhead of btrees. And there’s a fourth number to calculate based on
> >>> the compression level used. Having each of these numbers will be
> >>> useful as well as the calculations they’ll enable (ie, dead bytes in
> >>> file, bytes used for overhead, compression ratio achieved, etc).
> >>>
> >>>
> >>> couch_proc_manager -
> >>>
> >>>
> >>> We need to implement the hard ceiling for capping the number of OS
> >>> processes. We’ve started seeing a need for this at Cloudant with some
> >>> work loads so motivation to fix this is high. The only failing etap is
> >>> the assertion of this ceiling.
> >>>
> >>>
> >>> Synchronous db delete on Windows -
> >>>
> >>>
> >>> I did this because running the test suite was driving me bonkers. I
> >>> need to ask Dave about how this behaves on Windows (my guess is not
> >>> well) but I think we can close things up so that it works better than
> >>> the status quo.
> >>
> >
> >
> >
> > --
> > Iris Couch
>



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