Hi everyone, The pull request is open and ready for review: https://github.com/apache/couchdb/pull/3889
In summary, I think we managed to track the collation versions in views in a backwards compatible manner. There is a new view info map in the header which can be used in the future to record additional metadata about views (couchjs versions?, etc). With a slight bit of trickery, the views can also be transparently downgraded to the 3.2.1 version without a signature change or a view reset. Views which have more than one collator version will be submitted for re-compaction to the already existing smoosh upgrade views channel. The automatic trigger can be disabled as well with a new config option. As far as HTTP API differences these two endpoints now emit additional collator version info: _design/*/_info "view_index" has a "collator_versions" list which shows the list of versions for that particular view _node/*/_versions "collation_driver" object has a new "collator_version" which shows the collator version An example of this can be seen in https://github.com/apache/couchdb/pull/3889#issuecomment-1022643789 Thanks to everyone who participated in the discussion! Let's continue the review in the PR comments Cheers, -Nick On Tue, Jan 25, 2022 at 10:15 AM Nick Vatamaniuc <vatam...@gmail.com> wrote: > > Good idea, Will, to return the current collator version in the > `/_node/_local/_versions` output. We return the collation algorithm > and the library versions, however, since we switched to tracking the > opaque collator version, it's good to also expose that too. > > On Tue, Jan 25, 2022 at 9:47 AM Will Young <lostnetwork...@gmail.com> wrote: > > > > Hi Nick, > > > > The view _info setup looks good to me. Maybe it would be helpful to > > print the current runtime's collator and icu versions somewhere like > > the / meta or /node/ _system endpoint? I think that would provide a > > way to cross-reference to alleviate the drawback of the collator being > > the least human readable version (though only to find a more readable > > version for the views that are from the current runtime,) and maybe to > > debug oddities like a cluster somehow having nodes that are out of > > sync on libicu versions, or just to make it easier to check if dbs are > > going to be rebuilt after an update. Of course there are also other > > ways for an admin to examine the current runtime and workout versions > > so it is probably a question of how frequently it will come up. > > > > Thanks, > > Will > > > > Am Di., 25. Jan. 2022 um 07:45 Uhr schrieb Nick Vatamaniuc > > <vatam...@gmail.com>: > > > > > > Another update regarding the draft PR. > > > > > > There are now upgrade tests to see how we handle older 2.x, 3.2.1, and > > > views with multiple collator versions in them. > > > > > > The last commit modifies the _design/*/_info API to return the list of > > > collator versions to the user and wanted to see what everyone thought > > > about it: > > > > > > https://github.com/apache/couchdb/pull/3889#issuecomment-1020861208 > > > > > > Thanks, > > > -Nick > > > > > > On Tue, Jan 11, 2022 at 1:06 PM Nick Vatamaniuc <vatam...@gmail.com> > > > wrote: > > > > > > > > I threw together a draft PR https://github.com/apache/couchdb/pull/3889 > > > > > > > > Would that work? There are two tricks there - re-using a field > > > > position from an older <2.3.1 format, this should allow transparently > > > > downgrading back to 3.2.1 as we ignore that field there. Also, used a > > > > map so it should allow adding extra info to the views in the future > > > > (custom collation tailorings?). > > > > > > > > Thanks, > > > > -Nick > > > > > > > > On Sat, Nov 20, 2021 at 12:32 PM Nick Vatamaniuc <vatam...@gmail.com> > > > > wrote: > > > > > > > > > > Thanks, Adam. And thanks for the tip about the view header, Bob. > > > > > > > > > > Wonder if a disk version would make sense for views. Noticed Eric did > > > > > a nice job transparently migrating 2.x -> 3.x view files when we > > > > > removed key seq indices. Perhaps something like that would work for > > > > > adding a collator version. > > > > > > > > > > Cheers, > > > > > -Nick > > > > > > > > > > On Fri, Nov 19, 2021 at 9:09 AM Adam Kocoloski <kocol...@apache.org> > > > > > wrote: > > > > > > > > > > > > That seems like a smart solution Nick. > > > > > > > > > > > > Adam > > > > > > > > > > > > > On Nov 19, 2021, at 7:28 AM, Robert Newson <b...@rsn.io> wrote: > > > > > > > > > > > > > > Noting that the upgrade channel for views was misconceived (by > > > > > > > me) as there is no version number in the header for them. You’d > > > > > > > need to add it. > > > > > > > > > > > > > > B. > > > > > > > > > > > > > >> On 18 Nov 2021, at 07:12, Nick Vatamaniuc <vatam...@gmail.com> > > > > > > >> wrote: > > > > > > >> > > > > > > >> Thinking more about this issue I wonder if we can avoid > > > > > > >> resetting and > > > > > > >> rebuilding everything from scratch, and instead, let the upgrade > > > > > > >> happen in the background, while still serving the existing view > > > > > > >> data. > > > > > > >> > > > > > > >> The realization was that collation doesn't affect the emitted > > > > > > >> keys and > > > > > > >> values themselves, only their order in the view b-trees. That > > > > > > >> means > > > > > > >> we'd just have to rebuild b-trees, and that is exactly what our > > > > > > >> view > > > > > > >> compactor already does. > > > > > > >> > > > > > > >> When we detect a libicu version discrepancy we'd submit the view > > > > > > >> for > > > > > > >> compaction. We even have a dedicated "upgrade" [1] channel in > > > > > > >> smoosh > > > > > > >> which handles file version format upgrades, but we'll tweak that > > > > > > >> logic > > > > > > >> to trigger on libicu version mismatches as well. > > > > > > >> > > > > > > >> Would this work? Does anyone see any issue with that approach? > > > > > > >> > > > > > > >> [1] > > > > > > >> https://github.com/apache/couchdb/blob/3.x/src/smoosh/src/smoosh_server.erl#L435-L442 > > > > > > >> > > > > > > >> Cheers, > > > > > > >> -Nick > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >>> On Fri, Oct 29, 2021 at 7:01 PM Nick Vatamaniuc > > > > > > >>> <vatam...@apache.org> wrote: > > > > > > >>> > > > > > > >>> Hello everyone, > > > > > > >>> > > > > > > >>> CouchDB by default uses the libicu library to sort its view > > > > > > >>> rows. > > > > > > >>> When views are built, we do not record or track the version of > > > > > > >>> the > > > > > > >>> collation algorithm. The issue is that the ICU library may > > > > > > >>> modify the > > > > > > >>> collation order between major libicu versions, and when that > > > > > > >>> happens, > > > > > > >>> views built with the older versions may experience data loss. I > > > > > > >>> wanted > > > > > > >>> to discuss the option to record the libicu collator version in > > > > > > >>> each > > > > > > >>> view then warn the user when there is a mismatch. Also, > > > > > > >>> optionally > > > > > > >>> ignore the mismatch, or automatically rebuild the views. > > > > > > >>> > > > > > > >>> Imagine, for example, searching patient records using start/end > > > > > > >>> keys. > > > > > > >>> It could be possible that, say, the first letter of their name > > > > > > >>> now > > > > > > >>> collates differently in a new libicu. That would prevent the > > > > > > >>> patient > > > > > > >>> record from showing up in the view results for some important > > > > > > >>> procedure or medication. Users might not even be aware of this > > > > > > >>> kind of > > > > > > >>> data loss occurring, there won't be any error in the API or > > > > > > >>> warning in > > > > > > >>> the logs. > > > > > > >>> > > > > > > >>> I was thinking how to solve this. There were a few commits > > > > > > >>> already to > > > > > > >>> cleanup our collation drivers [1], expose libicu and collation > > > > > > >>> algorithm version in the new _versions endpoint [2], and some > > > > > > >>> other > > > > > > >>> minor fixes in that area. As the next steps we could: > > > > > > >>> > > > > > > >>> 1) Modify our views to keep track of the collation algorithm > > > > > > >>> version. We could attempt to transparently upgrade the view > > > > > > >>> header > > > > > > >>> format -- read the old view file, update the header with an > > > > > > >>> extra > > > > > > >>> libicu collation version field, that updates the signature, and > > > > > > >>> then, > > > > > > >>> save the file with the new header and new signature. This > > > > > > >>> avoids view > > > > > > >>> rebuilds, just records the collator version in the view and > > > > > > >>> moves the > > > > > > >>> files to a new name. > > > > > > >>> > > > > > > >>> 2) Do what PostgreSQL does, and 2a) emit a warning with the view > > > > > > >>> results when the current libicu version doesn't match the > > > > > > >>> version in > > > > > > >>> the view [3]. That means altering the view results to add a > > > > > > >>> "warning": > > > > > > >>> "..." field. Another alternative 2b) is emit a warning in the > > > > > > >>> _design/$ddoc/_info only. Users would have to know that after > > > > > > >>> an OS > > > > > > >>> version upgrade, or restoring backups, to make sure to look at > > > > > > >>> their > > > > > > >>> _design/$ddoc/_info for each db for each ddoc. Of course, there > > > > > > >>> may be > > > > > > >>> users which used the "raw" collation option, or know they are > > > > > > >>> using > > > > > > >>> just the plain ASCII character sets in their views. So we'd > > > > > > >>> have a > > > > > > >>> configuration setting to ignore the warnings as well. > > > > > > >>> > > > > > > >>> 3) Users who see the warning, could then either rebuild the view > > > > > > >>> with the new collator library manually, or it could happen > > > > > > >>> automatically based on a configuration option, basically "when > > > > > > >>> collator versions are miss-matched, invalidate and rebuild all > > > > > > >>> the > > > > > > >>> views". > > > > > > >>> > > > > > > >>> 4) We'd have a way for the users to assert (POST a ddoc update) > > > > > > >>> that > > > > > > >>> they double-checked the new ICU version and are convinced that a > > > > > > >>> particular view would not experience data loss with the new > > > > > > >>> collator. > > > > > > >>> That should make the warning go away, and the view to not be > > > > > > >>> rebuilt. > > > > > > >>> This can't be just a naive "collator" option setting as both > > > > > > >>> per-view > > > > > > >>> and per-design options are used when computing the view > > > > > > >>> signature, and > > > > > > >>> any changes there would result in the view being rebuilt. > > > > > > >>> Perhaps we > > > > > > >>> can add it to the design docs as a separate option which is > > > > > > >>> excluded > > > > > > >>> from the signature hash, like the "autoupdate" setting for > > > > > > >>> background > > > > > > >>> index builder ("collation_version_accept"?). PostgreSQL also > > > > > > >>> offers > > > > > > >>> this option with the ALTER COLLATION ... REFRESH VERSION > > > > > > >>> command [3] > > > > > > >>> > > > > > > >>> What do we think, is this a reasonable approach? Is there > > > > > > >>> something > > > > > > >>> easier / simpler we can do? > > > > > > >>> > > > > > > >>> Thanks! > > > > > > >>> -Nick > > > > > > >>> > > > > > > >>> [1] > > > > > > >>> https://github.com/apache/couchdb/pull/3746/commits/28f26f52fe2e170d98658311dafa8198d96b8061 > > > > > > >>> [2] > > > > > > >>> https://github.com/apache/couchdb/commit/c1bb4e4856edd93255d75ebe158b4da38bbf3333 > > > > > > >>> [3] https://www.postgresql.org/docs/13/sql-altercollation.html > > > > > > > > > > > > >
