[WIP] ✨ Add support for implicit paging in un/structured clients #1358

nimrodshn · 2021-01-24T09:00:21Z

What this does?

Following #341 this patch adds implicit paging to the un/structured clients. Fixes #532.

Thoughts about the API:

This patch opts for adding a new Method called ListPages: This method lists large data in "chunks" using the Continue curser token with a callback to be used by the user.

Open Questions:

Should ListPages be part of the Reader interface?

@ncdc @DirectXMan12 @vincepri @cben PTAL.

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k8s-ci-robot · 2021-01-24T09:00:32Z

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coderanger · 2021-01-24T09:04:48Z

This feels weird to me. What is the use case for this? Generally when a pagination cursor exists, not using it will lead to lots of weird race condition bugs when the object set changes between requests.

nimrodshn · 2021-01-24T09:14:20Z

@coderanger I tend to agree. I guess the idea is to hide the use of Continue from the user. Albeit the user can simply use Continue and view pages of data as it is now. Please refer to #532 for more information.

coderanger · 2021-01-24T09:20:56Z

I don't think this is what #532 was referring to. In what situation would you ever want to ask for "page 4 of the results" when you have no idea what that will even contain? The only time I could see someone doing that is in error when they want to get all items via pagination, but using this code they would get all those bugs I mentioned, which is why a pagination cursor is returned.

nimrodshn · 2021-01-24T09:23:28Z

@coderanger I had implemented it this way b/c I thought that is what reported in #532 - how do you view it?

coderanger · 2021-01-24T09:26:39Z

That List() would automatically check if a continue token was returned, and (give or take an option flag) automatically fetch the next page and combine it with the the results you already have, and repeat until no more data is returned. When accessing a huge list of objects that change frequently (e.g. all Pods) this can spread out the load on the API server, trading increased effective latency to remove the massive IO spike that could disrupt API server stability.

coderanger · 2021-01-24T09:27:53Z

Or there's the option @vincepri mentioned of doing a similar looped get with an iterator function callback so you never have to hold the full list of objects in memory at once. Both could be useful in different situations.

nimrodshn · 2021-01-24T09:29:36Z

@coderanger Interesting.. I will try and tackle those ideas. Indeed this implementation is fairly naive.

nimrodshn · 2021-01-26T08:07:19Z

@coderanger Please re-tal; specifically at the implementation at the typed_client.go - is this the direction you had in mind? what about the callback do you think it is necessary? Should we add the ListPages method to the Reader interface?

cc: @cben

coderanger · 2021-01-26T19:09:44Z

pkg/client/options.go

@@ -23,6 +23,11 @@ import (
 	"k8s.io/apimachinery/pkg/selection"
 )

+const (
+	// DefaultPageLimit represents the default limit used when specifyinh the 'Page' ListOption.
+	DefaultPageLimit = 100


This probably needs a better name since it's not the default for List() too.

@vincepri @cben Any suggestions?

pkg/client/options.go

pkg/client/typed_client.go

coderanger · 2021-01-26T19:16:17Z

pkg/client/typed_client.go

+		if err != nil {
+			return err
+		}
+		allItems = append(allItems, items...)


We don't want both a callback function and a huge list return, we should pick one pattern or the other (or move them to separate functions/options). The reason to use a visitor callback function is to avoid keeping the whole list in memory. I think it would be more Go-like to just do the callback style probably, ExtractList() requires a lot of runtime reflect magic since there is no unified API for accessing list items. But having both available could be convenient.

@vincepri Do you have opinions on which API to support (or both)?

Gotcha. 👍

@coderanger Actoually thinking about it - if the user would like to accumulate the result she can simply use the same ExtractList inside the callback.

That is, she can pass something like this:

out := &corev1.Pods{} allItems := make([]runtime.Object, 0) cl.ListPages(ctx, out, func(obj client.ObjectList) error { items, err := apimeta.ExtractList(interimResult) if err != nil { return err } allItems = append(allItems, items...) return nil })

Indeed, or more likely cast it to the correct type and skip needing ExtractList :)

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k8s-ci-robot · 2021-06-23T05:41:22Z

@nimrodshn: PR needs rebase.

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k8s-ci-robot added the cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. label Jan 24, 2021

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k8s-ci-robot requested review from alvaroaleman and DirectXMan12 January 24, 2021 09:00

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nimrodshn changed the title ~~:sperkles: Add support for implicit paging in un/structured clients~~ [WIP] :sperkles: Add support for implicit paging in un/structured clients Jan 24, 2021

k8s-ci-robot added the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Jan 24, 2021

nimrodshn changed the title ~~[WIP] :sperkles: Add support for implicit paging in un/structured clients~~ [WIP] ✨ Add support for implicit paging in un/structured clients Jan 25, 2021

nimrodshn force-pushed the implicit_implementation_of_paging branch from 974f336 to d3492ab Compare January 26, 2021 08:01

nimrodshn force-pushed the implicit_implementation_of_paging branch from d3492ab to b445caa Compare January 26, 2021 08:10

coderanger reviewed Jan 26, 2021

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nimrodshn force-pushed the implicit_implementation_of_paging branch 2 times, most recently from ea71907 to 370a5b9 Compare January 27, 2021 07:58

Add support for implicit paging in un/structured clients

7b60362

nimrodshn force-pushed the implicit_implementation_of_paging branch from 370a5b9 to 7b60362 Compare January 27, 2021 08:26

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k8s-ci-robot added the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label Jun 23, 2021

nimrodshn closed this Jul 11, 2021

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[WIP] ✨ Add support for implicit paging in un/structured clients #1358

[WIP] ✨ Add support for implicit paging in un/structured clients #1358

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[WIP] ✨ Add support for implicit paging in un/structured clients #1358

[WIP] ✨ Add support for implicit paging in un/structured clients #1358

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nimrodshn commented Jan 24, 2021 • edited Loading

What this does?

Thoughts about the API:

Open Questions:

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