> `update_seq` - is same as earlier. Not entirely sure on the intent there.
I just recall another reason why I did this. It helps with etag generation.
I am not going to add it to the spec for now.
On 2020/04/23 21:15:05, Paul Davis <paul.joseph.da...@gmail.com> wrote:
> I'd agree that my initial reaction to cursor was that its not a great
> fit, but there does seem to be the existing name used in the greater
> REST world for this sort of pagination so I'm not concerned about
> using that terminology.
>
> I'm generally on board with allowing and setting some default sane
> limits on pages. We probably should have done that quite awhile ago
> after moving to native clustering and now that we have FDB limits I
> think it makes even more sense to have an API that does not lend
> itself to crazy errors when people are just trying to poke at an API.
>
> I think we're all on board that one of the goals is to make sure that
> clients don't accidentally misinterpret a response. That is, we're
> trying to be quite diligent that a user doesn't get 1000 rows and not
> realize there's another 10 that were beyond the limit. The bookmark
> approach with hard caps seems like a generally fine approach to me.
> The current approach users extra URL path segments to try and avoid
> this confusion. I wonder if we should consider starting to properly
> version our API using one of the many schemes that are used. Having
> read through a few articles I don't have a very clear favorite though.
>
> As to this particular proposal I do see a couple issues:
>
> `total` - We can do this in most cases fairly easily. Though it's a
> bit odd for continuous changes.
>
> `complete` - I'm not sure whether this is entirely possible given the
> API that FDB presents us. Specifically, when we set a range and we get
> back exactly $num_rows in the response, if the data set ended at
> exactly that page I don't think the `more` flag from fdb would tell us
> that. So we'd have a clunky UX there where we say not complete but the
> next page is empty. That's also not to mention that depending on
> whether we're looking at snapshots and so on that there's no way for
> us to know between stateless requests whether there were more rows
> added to the end.
>
> `page` - This one is just hard/impossible to calculate. FDB doesn't
> provide us with offsets or even an efficient "about how many rows in
> this range?" type queries so providing that would be both inaccurate
> and fairly difficult/expensive to calculate. In some cases I think we
> could have something maybe close that didn't suck too badly, but it'd
> also fall down for changes as well due to the way that updates reorder
> them.
>
> `update_seq` - I'm just not sure on when this would be useful or what
> it would refer to. Maybe a version stamp of the last change for that
> request? If we had a future API that asked for a snapshot access then
> maybe? But if we did do something there with versionstamps or read
> versions I'd expect that to come with the rest of the API.
>
> For the bookmark fields:
>
> `direction` vs `descending` seems like a field duplication to me.
>
> `page` - This would seem to suggest we could skip to a certain
> location in the results numerically which we are not able to do with
> the FDB API.
>
> `last_key` vs `start_key` seems like a field duplication. We don't
> need to know where things started I don't think. Just where to start
> from and where to end.
>
> `update_seq` - is same as earlier. Not entirely sure on the intent there.
>
> `timestamp` - Expiring bookmarks based on time does not seem like a
> good idea. Both for clock skew and why bother when this would
> functionally just be a convenience API that users could already
> implement for themselves.
>
> Another thing might also be to provide our bookmark as a full link
> that seems to be fairly standard REST practice these days. Something
> that clients don't have to do any logic with so that we're free to
> change the implementation.
>
> And lastly, I don't think we should be neglecting the _changes API as
> part of this discussion. I realize that we'll need to support the
> older streaming semantics if we want to maintain replication
> compatibility (which I think we'll all agree is a Good Thing) but it
> also feels a bit wrong to ignore it as part of this work if we're
> going to be modernizing our APIs. Though if we do pick up a good
> versioning scheme then we could theoretically make those changes
> easily enough. Plus, who doesn't want to rewrite chttpd to be a whole
> lot less... chttpd-y?
>
>
> On Thu, Apr 23, 2020 at 1:43 PM Robert Samuel Newson <rnew...@apache.org>
> wrote:
> >
> >
> > I think it's a key difference from "cursor" as I've seen them elsewhere,
> > that ours will point at an ever changing database, you couldn't seamlessly
> > cursor through a large data set, one "page" at a time.
> >
> > Bookmarks began in search (raises guilty hand) in order to address a
> > Lucene-specific issue (that high values of "skip" are incredibly
> > inefficient, using lots of RAM). That is not true for CouchDB's own
> > indexes, which can be navigated perfectly with
> > startkey/endkey/startkey_docid/endkey_docid, etc.
> >
> > I guess I'm not helping much with these observations but I wouldn't like to
> > see CouchDB gain an additional and ugly method of doing something already
> > possible.
> >
> > B.
> >
> > > On 23 Apr 2020, at 19:02, Joan Touzet <woh...@apache.org> wrote:
> > >
> > > I realise this is bikeshedding, but I guess that's kind of the point...
> > > Everything below is my opinion, not "fact."
> > >
> > > It's unfortunate we need a new endpoint for all of this. In a vacuum I
> > > might have just suggested we use the semantics we already have, perhaps
> > > with ?from= instead of ?since= .
> > >
> > > "page" only works if the size of a page is well known, either by server
> > > preference or directly in the URL. If I ask for:
> > >
> > > GET /{db}/_all_docs?limit=20&page=3
> > >
> > > I know that I'm always going to get document 41 through 60 in the default
> > > collation order.
> > >
> > > There's a *fantastic* summary of examples from popular REST APIs here:
> > >
> > > https://medium.com/@ignaciochiazzo/paginating-requests-in-apis-d4883d4c1c4c
> > >
> > > We are *pretty close* to what a cursor means in those other examples,
> > > except for the fact that our cursor can go stale/invalid after a short
> > > time.
> > >
> > > Bob, could you be a bit more detailed in your explanation how our
> > > definition isn't close to these? Or did you mean SQL CURSOR (which is
> > > something entirely different?) If so, I'm fine with this being a REST API
> > > cursor - something clearly distinct.
> > >
> > > I come back to wanting to preserve the existing endpoint syntax and
> > > naming, without new endpoints, but specifying this new FDB token via
> > > ?cursor= and this being the trigger for the new behaviour. At some point,
> > > we simply stop accepting ?since= tokens. This seems inline with other
> > > popular REST APIs.
> > >
> > > -Joan "still sick and not sleeping right" Touzet
> > >
> > >
> > > On 2020-04-23 12:30, Robert Newson wrote:
> > >> cursor has established meaning in other databases and ours would not be
> > >> very close to them. I don’t think it’s a good idea.
> > >> B.
> > >>> On 23 Apr 2020, at 11:50, Ilya Khlopotov <iil...@apache.org> wrote:
> > >>>
> > >>>
> > >>>>
> > >>>> The best I could come up with is replacing page with
> > >>>> cursor - {db}/_all_docs/cursor or possibly {db}/_cursor/_all_docs
> > >>> Good idea, I like {db}/_all_docs/cursor (or {db}/_all_docs/_cursor).
> > >>>
> > >>>> On 2020/04/23 08:54:36, Garren Smith <gar...@apache.org> wrote:
> > >>>> I agree with Bob that page doesn't make sense as an endpoint. I'm also
> > >>>> rubbish with naming. The best I could come up with is replacing page
> > >>>> with
> > >>>> cursor - {db}/_all_docs/cursor or possibly {db}/_cursor/_all_docs
> > >>>> All the fields in the bookmark make sense except timestamp. Why would
> > >>>> it
> > >>>> matter if the timestamp is old? What happens if a node's time is an
> > >>>> hour
> > >>>> behind another node?
> > >>>>
> > >>>>
> > >>>>> On Thu, Apr 23, 2020 at 4:55 AM Ilya Khlopotov <iil...@apache.org>
> > >>>>> wrote:
> > >>>>>
> > >>>>> - page is to provide some notion of progress for user
> > >>>>> - timestamp - I was thinking that we should drop requests if user
> > >>>>> would
> > >>>>> try to pass bookmark created an hour ago.
> > >>>>>
> > >>>>> On 2020/04/22 21:58:40, Robert Samuel Newson <rnew...@apache.org>
> > >>>>> wrote:
> > >>>>>> "page" and "page number" are odd to me as these don't exist as
> > >>>>>> concepts,
> > >>>>> I'd rather not invent them. I note there's no mention of page size,
> > >>>>> which
> > >>>>> makes "page number" very vague.
> > >>>>>>
> > >>>>>> What is "timestamp" in the bookmark and what effect does it have when
> > >>>>> the bookmark is passed back in?
> > >>>>>>
> > >>>>>> I guess, why does the bookmark include so much extraneous data? Items
> > >>>>> that are not needed to find the fdb key to begin the next response
> > >>>>> from.
> > >>>>>>
> > >>>>>>
> > >>>>>>> On 22 Apr 2020, at 21:18, Ilya Khlopotov <iil...@apache.org> wrote:
> > >>>>>>>
> > >>>>>>> Hello everyone,
> > >>>>>>>
> > >>>>>>> Based on the discussions on the thread I would like to propose a
> > >>>>> number of first steps:
> > >>>>>>> 1) introduce new endpoints
> > >>>>>>> - {db}/_all_docs/page
> > >>>>>>> - {db}/_all_docs/queries/page
> > >>>>>>> - _all_dbs/page
> > >>>>>>> - _dbs_info/page
> > >>>>>>> - {db}/_design/{ddoc}/_view/{view}/page
> > >>>>>>> - {db}/_design/{ddoc}/_view/{view}/queries/page
> > >>>>>>> - {db}/_find/page
> > >>>>>>>
> > >>>>>>> These new endpoints would act as follows:
> > >>>>>>> - don't use delayed responses
> > >>>>>>> - return object with following structure
> > >>>>>>> ```
> > >>>>>>> {
> > >>>>>>> "total": Total,
> > >>>>>>> "bookmark": base64 encoded opaque value,
> > >>>>>>> "completed": true | false,
> > >>>>>>> "update_seq": when available,
> > >>>>>>> "page": current page number,
> > >>>>>>> "items": [
> > >>>>>>> ]
> > >>>>>>> }
> > >>>>>>> ```
> > >>>>>>> - the bookmark would include following data (base64 or
> > >>>>>>> protobuff???):
> > >>>>>>> - direction
> > >>>>>>> - page
> > >>>>>>> - descending
> > >>>>>>> - endkey
> > >>>>>>> - endkey_docid
> > >>>>>>> - inclusive_end
> > >>>>>>> - startkey
> > >>>>>>> - startkey_docid
> > >>>>>>> - last_key
> > >>>>>>> - update_seq
> > >>>>>>> - timestamp
> > >>>>>>> ```
> > >>>>>>>
> > >>>>>>> 2) Implement per-endpoint configurable max limits
> > >>>>>>> ```
> > >>>>>>> _all_docs = 5000
> > >>>>>>> _all_docs/queries = 5000
> > >>>>>>> _all_dbs = 5000
> > >>>>>>> _dbs_info = 5000
> > >>>>>>> _view = 2500
> > >>>>>>> _view/queries = 2500
> > >>>>>>> _find = 2500
> > >>>>>>> ```
> > >>>>>>>
> > >>>>>>> Latter (after few years) CouchDB would deprecate and remove old
> > >>>>> endpoints.
> > >>>>>>>
> > >>>>>>> Best regards,
> > >>>>>>> iilyak
> > >>>>>>>
> > >>>>>>> On 2020/02/19 22:39:45, Nick Vatamaniuc <vatam...@apache.org> wrote:
> > >>>>>>>> Hello everyone,
> > >>>>>>>>
> > >>>>>>>> I'd like to discuss the shape and behavior of streaming APIs for
> > >>>>> CouchDB 4.x
> > >>>>>>>>
> > >>>>>>>> By "streaming APIs" I mean APIs which stream data in row as it gets
> > >>>>>>>> read from the database. These are the endpoints I was thinking of:
> > >>>>>>>>
> > >>>>>>>> _all_docs, _all_dbs, _dbs_info and query results
> > >>>>>>>>
> > >>>>>>>> I want to focus on what happens when FoundationDB transactions
> > >>>>>>>> time-out after 5 seconds. Currently, all those APIs except
> > >>>>>>>> _changes[1]
> > >>>>>>>> feeds, will crash or freeze. The reason is because the
> > >>>>>>>> transaction_too_old error at the end of 5 seconds is retry-able by
> > >>>>>>>> default, so the request handlers run again and end up shoving the
> > >>>>>>>> whole request down the socket again, headers and all, which is
> > >>>>>>>> obviously broken and not what we want.
> > >>>>>>>>
> > >>>>>>>> There are few alternatives discussed in couchdb-dev channel. I'll
> > >>>>>>>> present some behaviors but feel free to add more. Some ideas might
> > >>>>>>>> have been discounted on the IRC discussion already but I'll present
> > >>>>>>>> them anyway in case is sparks further conversation:
> > >>>>>>>>
> > >>>>>>>> A) Do what _changes[1] feeds do. Start a new transaction and
> > >>>>>>>> continue
> > >>>>>>>> streaming the data from the next key after last emitted in the
> > >>>>>>>> previous transaction. Document the API behavior change that it may
> > >>>>>>>> present a view of the data is never a point-in-time[4] snapshot of
> > >>>>>>>> the
> > >>>>>>>> DB.
> > >>>>>>>>
> > >>>>>>>> - Keeps the API shape the same as CouchDB <4.0. Client libraries
> > >>>>>>>> don't have to change to continue using these CouchDB 4.0 endpoints
> > >>>>>>>> - This is the easiest to implement since it would re-use the
> > >>>>>>>> implementation for _changes feed (an extra option passed to the
> > >>>>>>>> fold
> > >>>>>>>> function).
> > >>>>>>>> - Breaks API behavior if users relied on having a point-in-time[4]
> > >>>>>>>> snapshot view of the data.
> > >>>>>>>>
> > >>>>>>>> B) Simply end the stream. Let the users pass a `?transaction=true`
> > >>>>>>>> param which indicates they are aware the stream may end early and
> > >>>>>>>> so
> > >>>>>>>> would have to paginate from the last emitted key with a skip=1.
> > >>>>>>>> This
> > >>>>>>>> will keep the request bodies the same as current CouchDB. However,
> > >>>>>>>> if
> > >>>>>>>> the users got all the data one request, they will end up wasting
> > >>>>>>>> another request to see if there is more data available. If they
> > >>>>>>>> didn't
> > >>>>>>>> get any data they might have a too large of a skip value (see [2])
> > >>>>>>>> so
> > >>>>>>>> would have to guess different values for start/end keys. Or impose
> > >>>>>>>> max
> > >>>>>>>> limit for the `skip` parameter.
> > >>>>>>>>
> > >>>>>>>> C) End the stream and add a final metadata row like a
> > >>>>>>>> "transaction":
> > >>>>>>>> "timeout" at the end. That will let the user know to keep
> > >>>>>>>> paginating
> > >>>>>>>> from the last key onward. This won't work for `_all_dbs` and
> > >>>>>>>> `_dbs_info`[3] Maybe let those two endpoints behave like _changes
> > >>>>>>>> feeds and only use this for views and and _all_docs? If we like
> > >>>>>>>> this
> > >>>>>>>> choice, let's think what happens for those as I couldn't come up
> > >>>>>>>> with
> > >>>>>>>> anything decent there.
> > >>>>>>>>
> > >>>>>>>> D) Same as C but to solve the issue with skips[2], emit a bookmark
> > >>>>>>>> "key" of where the iteration stopped and the current "skip" and
> > >>>>>>>> "limit" params, which would keep decreasing. Then user would pass
> > >>>>>>>> those in "start_key=..." in the next request along with the limit
> > >>>>>>>> and
> > >>>>>>>> skip params. So something like "continuation":{"skip":599,
> > >>>>>>>> "limit":5,
> > >>>>>>>> "key":"..."}. This has the same issue with array results for
> > >>>>>>>> `_all_dbs` and `_dbs_info`[3].
> > >>>>>>>>
> > >>>>>>>> E) Enforce low `limit` and `skip` parameters. Enforce maximum
> > >>>>>>>> values
> > >>>>>>>> there such that response time is likely to fit in one transaction.
> > >>>>>>>> This could be tricky as different runtime environments will have
> > >>>>>>>> different characteristics. Also, if the timeout happens there
> > >>>>>>>> isn't a
> > >>>>>>>> a nice way to send an HTTP error since we already sent the 200
> > >>>>>>>> response. The downside is that this might break how some users use
> > >>>>>>>> the
> > >>>>>>>> API, if say the are using large skips and limits already. Perhaps
> > >>>>>>>> here
> > >>>>>>>> we do both B and D, such that if users want transactional behavior,
> > >>>>>>>> they specify that `transaction=true` param and only then we enforce
> > >>>>>>>> low limit and skip maximums.
> > >>>>>>>>
> > >>>>>>>> F) At least for `_all_docs` it seems providing a point-in-time
> > >>>>>>>> snapshot view doesn't necessarily need to be tied to transaction
> > >>>>>>>> boundaries. We could check the update sequence of the database at
> > >>>>>>>> the
> > >>>>>>>> start of the next transaction and if it hasn't changed we can
> > >>>>>>>> continue
> > >>>>>>>> emitting a consistent view. This can apply to C and D and would
> > >>>>>>>> just
> > >>>>>>>> determine when the stream ends. If there are no writes happening to
> > >>>>>>>> the db, this could potential streams all the data just like option
> > >>>>>>>> A
> > >>>>>>>> would do. Not entirely sure if this would work for views.
> > >>>>>>>>
> > >>>>>>>> So what do we think? I can see different combinations of options
> > >>>>>>>> here,
> > >>>>>>>> maybe even different for each API point. For example `_all_dbs`,
> > >>>>>>>> `_dbs_info` are always A, and `_all_docs` and views default to A
> > >>>>>>>> but
> > >>>>>>>> have parameters to do F, etc.
> > >>>>>>>>
> > >>>>>>>> Cheers,
> > >>>>>>>> -Nick
> > >>>>>>>>
> > >>>>>>>> Some footnotes:
> > >>>>>>>>
> > >>>>>>>> [1] _changes feeds is the only one that works currently. It
> > >>>>>>>> behaves as
> > >>>>>>>> per RFC
> > >>>>> https://github.com/apache/couchdb-documentation/blob/master/rfcs/003-fdb-seq-index.md#access-patterns
> > >>>>> .
> > >>>>>>>> That is, we continue streaming the data by resetting the
> > >>>>>>>> transaction
> > >>>>>>>> object and restarting from the last emitted key (db sequence in
> > >>>>>>>> this
> > >>>>>>>> case). However, because the transaction restarts if a document is
> > >>>>>>>> updated while the streaming take place, it may appear in the
> > >>>>>>>> _changes
> > >>>>>>>> feed twice. That's a behavior difference from CouchDB < 4.0 and
> > >>>>>>>> we'd
> > >>>>>>>> have to document it, since previously we presented this
> > >>>>>>>> point-in-time
> > >>>>>>>> snapshot of the database from when we started streaming.
> > >>>>>>>>
> > >>>>>>>> [2] Our streaming APIs have both skips and limits. Since FDB
> > >>>>>>>> doesn't
> > >>>>>>>> currently support efficient offsets for key selectors
> > >>>>>>>> (
> > >>>>> https://apple.github.io/foundationdb/known-limitations.html#dont-use-key-selectors-for-paging
> > >>>>> )
> > >>>>>>>> we implemented skip by iterating over the data. This means that a
> > >>>>>>>> skip
> > >>>>>>>> of say 100000 could keep timing out the transaction without
> > >>>>>>>> yielding
> > >>>>>>>> any data.
> > >>>>>>>>
> > >>>>>>>> [3] _all_dbs and _dbs_info return a JSON array so they don't have
> > >>>>>>>> an
> > >>>>>>>> obvious place to insert a last metadata row.
> > >>>>>>>>
> > >>>>>>>> [4] For example they have a constraint that documents "a" and "z"
> > >>>>>>>> cannot both be in the database at the same time. But when iterating
> > >>>>>>>> it's possible that "a" was there at the start. Then by the end, "a"
> > >>>>>>>> was removed and "z" added, so both "a" and "z" would appear in the
> > >>>>>>>> emitted stream. Note that FoundationDB has APIs which exhibit the
> > >>>>>>>> same
> > >>>>>>>> "relaxed" constrains:
> > >>>>>>>>
> > >>>>> https://apple.github.io/foundationdb/api-python.html#module-fdb.locality
> > >>>>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>
> > >>>>
> >
>
