Thanks! For some reason your step 4 was elided in the GMail UI but not when Garren responded and I was confused.
On Fri, Mar 27, 2020 at 9:11 AM Glynn Bird <glynn.b...@gmail.com> wrote: > > > The quoting here is weird. Are you saying to skip _all_docs in your > proposal, Glynn? > > I'm saying eliminate (3) from your list of things. > > 1. If user specifies an index, use it even if we have to wait > 2. If an index is built that can be used, use it > 3. n/a > 4. As a last resort use _all_docs > > > On Thu, 26 Mar 2020 at 16:59, Paul Davis <paul.joseph.da...@gmail.com> > wrote: > > > On Thu, Mar 26, 2020 at 5:33 AM Will Holley <willhol...@gmail.com> wrote: > > > > > > Ah - in that case I think we should remove step 3, as it leads to a > > > confusing mental model. It's much simpler to explain that Mango will only > > > use fresh indexes and any new indexes will build in the background. > > > > > > > Simpler in some respect. The trade off being that we then have to > > teach users how to know that an index is built and also that they then > > need to be aware that different index types will have different ideas > > of what "built" means. > > > > > On Thu, 26 Mar 2020 at 10:15, Garren Smith <gar...@apache.org> wrote: > > > > > > > On Thu, Mar 26, 2020 at 11:04 AM Will Holley <willhol...@gmail.com> > > wrote: > > > > > > > > > Broadly, I think it's a big step forward if we can prevent Mango from > > > > > automatically selecting extremely stale indexes. > > > > > > > > > > I've been going back and forth on whether step 3 could lead to some > > > > > difficult-to-predict behaviour. If we assume that requests have a > > short > > > > > timeout - e.g. we can't return any result if it doesn't complete > > within > > > > the > > > > > FDB transaction timeout - then I think it's fine: queries that use > > > > > _all_docs and a large database will be timing out anyway. > > > > > > > > > > If we were to allow long-running queries then it seems a bit > > sketchier > > > > > because adding an index to a large database could cause queries that > > > > > previously completed to start timing out whilst they block on the > > index > > > > > build. This is basically how Mango in CouchDB 2/3 behaves and has > > been a > > > > > big pain point for customers I've worked with, to the point where you > > > > > basically need to explicitly specify which index Mango uses in all > > cases > > > > if > > > > > you're to avoid surprise timeouts when somebody adds a new index. > > > > > > > > > > As I understand it, we're not allowing queries to span FDB > > transactions > > > > so > > > > > this latter case is not something to worry about? > > > > > > > > > > > > We are going to allow queries to span transactions. This is already > > > > implemented for views and will be for mango > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > Will > > > > > > > > > > On Wed, 25 Mar 2020 at 19:43, Garren Smith <gar...@apache.org> > > wrote: > > > > > > > > > > > On Wed, Mar 25, 2020 at 8:35 PM Paul Davis < > > > > paul.joseph.da...@gmail.com> > > > > > > wrote: > > > > > > > > > > > > > > It was therefore felt that having an immediate "Not ready" > > signal > > > > for > > > > > > > just _some_ calls to _find, based on the type of backing index, > > was a > > > > > bad > > > > > > > and confusing api. > > > > > > > > > > > > > > > > We also discussed _find calls where the user does not specify > > an > > > > > index, > > > > > > > and concluded that we would be free to choose between using the > > > > > _all_docs > > > > > > > index (which is always up to date but rarely the best index for a > > > > given > > > > > > > selector) or blocking to update a better but stale index. > > > > > > > > > > > > > > > > Summary-ing my summarisation; > > > > > > > > > > > > > > > > 1) if you specify an index, we'll use it even if we have to > > update > > > > > it, > > > > > > > no matter how long that takes. > > > > > > > > 2) if you don't specify an index, it's the dealers choice. The > > > > > details > > > > > > > here may change in point releases. > > > > > > > > > > > > > > > > > > > > > > So it seems there's still a bit of confusion on what the > > consensus is > > > > > > > here. The way that I had thought this would work is that we'd do > > > > > > > something like such: > > > > > > > > > > > > > > 1. If user specifies and index, use it even if we have to wait > > > > > > > 2. If an index is built that can be used, use it > > > > > > > 3. If an index is building that can be used, wait for it > > > > > > > 4. As a last resort use _all_docs > > > > > > > > > > > > > > Discussing with Garren on the PR he's of the opinion that we > > should > > > > > > > skip step 3 and just go directly to using _all_docs if nothing is > > > > > > > built. > > > > > > > > > > > > > > > > > > > I just want to clarify step 3. I'm ok with using an index that > > still > > > > > needs > > > > > > to be built as long as there is no other built index > > > > > > that can service the request. > > > > > > > > > > > > So the big thing for me is to always prefer a built index over a > > > > building > > > > > > index. In the situation where there is only 1 building index > > versus all > > > > > > docs I'm ok with using the building index. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > My main assumption is that most cases where a user is creating an > > > > > > > index and then wanting to run a query with it are in the > > > > > > > design/exploration phase of learning the feature or designing an > > > > index > > > > > > > to use. In that scenario if we skip waiting it seems likely that > > a > > > > > > > user could easily be led to believe that an index creation > > "worked" > > > > > > > for their selector when in reality it was just backed by > > _all_docs. > > > > > > > > > > > > > > The other reason for preferring to wait for an index to finish > > > > > > > building is that the UI for the normal case of creating indexes > > is a > > > > > > > bit awkward. Having to run a polling loop around checking the > > index > > > > > > > status seems suboptimal in most cases. > > > > > > > > > > > > > > Am I missing other cases that would benefit from not waiting and > > just > > > > > > > using _all_docs? > > > > > > > > > > > > > > Paul > > > > > > > > > > > > > > > > > > > > > > > >
