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Type: Task
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Resolution: Fixed
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Priority: Major - P3
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Affects Version/s: 4.2.0
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Component/s: Internal Code
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Fully Compatible
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Service Arch 2021-02-22, Service Arch 2021-03-08
Opportunistic reads against replica-sets was originally introduced in v4.2 as part of PM-856. This feature allows mongos to direct secondary reads to any secondary with an active connection, instead of waiting for a new connection to a specific secondary.
Under certain workloads, as described in SERVER-53853, opportunistic reads may trigger construction of unnecessary connections to mongod processes, which would regress the overall performance.
This ticket should introduce a new feature flag to disable opportunistic reads in v4.2 by default. In particular, the following tickets from PM-856 introduce new functionality that we might want to guard with the feature flag: SERVER-41132, SERVER-41133, and SERVER-41134.
We may wan to approach this ticket from this for loop, introduced by SERVER-41133 (see excerpt below).
// Attempt to get a connection to every target host for (size_t idx = 0; idx < request.target.size() && !cmdState->finishLine.isReady(); ++idx) { auto connFuture = _pool->get(request.target[idx], request.sslMode, request.timeout); ... }
- is related to
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SERVER-53853 Large buildup of mongos to mongod connections and low performance with secondaryPreferred reads
- Closed