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* Docs: data requests and breaking changes edit * Update contribute/architecture/frontend-data-requests.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Fixes from review * Update contribute/architecture/frontend-data-requests.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Update contribute/architecture/frontend-data-requests.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Update contribute/breaking-changes-guide/breaking-changes-guide.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Fix from review * Update contribute/breaking-changes-guide/breaking-changes-guide.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Update contribute/breaking-changes-guide/breaking-changes-guide.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Fix from review * Update contribute/breaking-changes-guide/breaking-changes-guide.md Co-authored-by: Beverly Buchanan <131809838+BeverlyJaneJ@users.noreply.github.com> * Fixes from review * Update contribute/breaking-changes-guide/breaking-changes-guide.md Co-authored-by: Jack Baldry <jack.baldry@grafana.com> * Fix from review * Fix from review * Fix alt text * Remove 1st person * Fix from review * Eliminate 'in case' --------- Co-authored-by: Jack Baldry <jack.baldry@grafana.com> Co-authored-by: Beverly Buchanan <131809838+BeverlyJaneJ@users.noreply.github.com>
49 lines
3.2 KiB
Markdown
49 lines
3.2 KiB
Markdown
# Frontend data requests
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[BackendSrv](https://github.com/grafana/grafana/blob/main/packages/grafana-runtime/src/services/backendSrv.ts) handles all outgoing HTTP requests from Grafana. This document explains the high-level concepts used by `BackendSrv`.
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## Cancel requests
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While data sources can implement their own cancellation concept, we recommend that you use the method described in this section.
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A data request can take a long time to finish. During the time between when a request starts and finishes, the user can change context. For example, the user may navigate away or issue the same request again.
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If we wait for canceled requests to complete, they might create unnecessary load on the data sources.
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### Request cancellation by Grafana version
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Grafana uses a concept called _request cancellation_ to cancel any ongoing request that Grafana doesn't need. The process for canceling requests in this manner varies by Grafana version.
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#### Before Grafana 7.2
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Before Grafana can cancel any data request, it has to identify that request. Grafana identifies a request using the property `requestId` [passed as options](https://github.com/grafana/grafana/blob/main/packages/grafana-runtime/src/services/backendSrv.ts#L47) when you use [BackendSrv](https://github.com/grafana/grafana/blob/main/packages/grafana-runtime/src/services/backendSrv.ts).
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The cancellation logic is as follows:
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- When an ongoing request discovers that an additional request with the same `requestId` has started, then Grafana will cancel the ongoing request.
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- When an ongoing request discovers that the special "cancel all requests" `requestId` was sent, then Grafana will cancel the ongoing request.
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#### After Grafana 7.2
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Grafana 7.2 introduced an additional way of canceling requests using [RxJs](https://github.com/ReactiveX/rxjs). To support the new cancellation functionality, the data source needs to use the new `fetch` function in [BackendSrv](https://github.com/grafana/grafana/blob/main/packages/grafana-runtime/src/services/backendSrv.ts).
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Migrating the core data sources to the new `fetch` function is an ongoing process. To learn more, refer to [this issue](https://github.com/grafana/grafana/issues/27222).
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## Request queue
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If Grafana isn't configured to support HTTP/2, browsers connecting with HTTP 1.1 enforce a limit of 4 to 8 parallel requests (the specific limit varies). Because of this limit, if some requests take a long time, they will block later requests and make interacting with Grafana very slow.
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[Enabling HTTP/2 support in Grafana](https://grafana.com/docs/grafana/latest/administration/configuration/#protocol) allows far more parallel requests.
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### Before Grafana 7.2
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Not supported.
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### After Grafana 7.2
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Grafana uses a _request queue_ to process all incoming data requests in order while reserving a free "spot" for any requests to the Grafana API.
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Since the first implementation of the request queue doesn't take into account what browser the user uses, the request queue's limit for parallel data source requests is hard-coded to 5.
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> **Note:** Grafana instances [configured with HTTP/2](https://grafana.com/docs/grafana/latest/administration/configuration/#protocol) have a hard-coded limit of 1000.
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