feat(flags): Add query timeout as a limit config

[rohanprasad]

In the case of a multi-tenant environment, long-running queries by tenants can consume all the resources, starving the request from other tenants. The change adds query-timeout as a config which will be applied to all the query requests sent without timeout param.

Fixes DGRAPH-3184

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This change is 

[CLAassistant]

All committers have signed the CLA.

[ahsanbarkati]

Looks good.

[ahsanbarkati]

Actually, setting 500ms as timeout is causing various tests to fail.

[NamanJain8]

Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on @jarifibrahim and @rohanprasad)

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dgraph/cmd/alpha/http.go, line 137 at r1 (raw file):

// parses it into time.Duration, empty string is converted into zero value
func parseDuration(r *http.Request, name string, defaultVal time.Duration) (time.Duration, error) {
	value := r.URL.Query().Get(name)

I think we want to over-ride the query timeout set by the user if it is greater than the default value in a multi-tenant setup. @rohanprasad can you confirm this please?

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dgraph/cmd/alpha/http.go, line 162 at r1 (raw file):

		return
	}
	queryTimeout, err := parseDuration(r, "timeout", x.Config.QueryTimeout)

This will timeout the query made via HTTP endpoint /query. But the queries made via GRPC (see Server.Query) will not timeout.
I think in a multi-tenant system it will be useful to have a timeout there as well.

[rohanprasad]

Default set to 0

Reviewable status: 0 of 4 files reviewed, 2 unresolved discussions (waiting on @jarifibrahim, @NamanJain8, and @rohanprasad)

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dgraph/cmd/alpha/http.go, line 137 at r1 (raw file):

Previously, NamanJain8 (Naman Jain) wrote…

I think we want to over-ride the query timeout set by the user if it is greater than the default value in a multi-tenant setup. @rohanprasad can you confirm this please?

Confirmed, we don't want to override if the timeout is set by the user

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dgraph/cmd/alpha/http.go, line 162 at r1 (raw file):

Previously, NamanJain8 (Naman Jain) wrote…

This will timeout the query made via HTTP endpoint /query. But the queries made via GRPC (see Server.Query) will not timeout.
I think in a multi-tenant system it will be useful to have a timeout there as well.

Will do

[NamanJain8]

Looks good to me.

Changes done.