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From Garren Smith <gar...@apache.org>
Subject Re: [VOTE] Merge BigCouch
Date Wed, 08 May 2013 19:20:39 GMT
+1 

On 08 May 2013, at 7:04 PM, Joan Touzet <wohali@apache.org> wrote:

> +1
> 
> On Tue, May 07, 2013 at 04:02:09PM -0500, Paul Davis wrote:
>> +1
>> 
>> On Tue, May 7, 2013 at 3:52 PM, Russell Branca <chewbranca@gmail.com> wrote:
>>> +1
>>> 
>>> 
>>> Very excited to see this! Great work!
>>> 
>>> 
>>> -Russell
>>> 
>>> 
>>> On Tue, May 7, 2013 at 1:44 PM, Robert Newson <rnewson@apache.org> wrote:
>>> 
>>>> FYI: A zip of this work is available at
>>>> http://people.apache.org/~rnewson/dist/nebraska-merge-candidate.zip
>>>> made by 'git archive -o nebraska-merge-candidate.zip
>>>> nebraska-merge-candidate'
>>>> 
>>>> On 7 May 2013 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.
>>>> 
> 
> -- 
> Joan Touzet | joant@atypical.net | wohali everywhere else


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