39b5b601f8
* MM-30026: Use DB master when getting team members from a session A race condition happens when the read-replica isn't updated yet by the time a session expiry message reaches another node in the cluster. Here is the sequence of events that can cause it: - Server1 gets any request which has to wipe session cache. - The SQL query is written to DB master, and a cluster message is propagated to clear the session cache for that user. - Now before the read-replica is updated with the master’s update, the cluster message reaches Server2. The session cache is wiped out for that user. - _Any random_ request for that user hits Server2. Does NOT have to be the update team name request. The request does not find the value in session cache, because it’s wiped off, and picks it up from the DB. Surprise surprise, it gets the stale value. Sticks it into the cache. By now, the read-replica is updated. But guess what, we aren’t going to ask the DB anymore, because we have it in the cache. And the cache has the stale value. We use a temporary approach for now by introducing a context in the DB calls so that the useMaster information can be easily passed. And this has the added advantage of reusing the same context for future DB calls in case it happens. And we can also add more context keys as needed. A proper approach needs some architectural changes. See the issue for more details. ```release-note Fixed a bug where a session will hold on to a cached value in an HA setup with read-replicas configured. ``` * incorporate review comments Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
33 строки
919 B
Go
33 строки
919 B
Go
// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
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// See LICENSE.txt for license information.
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package sqlstore
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import "context"
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// storeContextKey is the base type for all context keys for the store.
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type storeContextKey string
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// contextValue is a type to hold some pre-determined context values.
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type contextValue string
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// Different possible values of contextValue.
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const (
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useMaster contextValue = "useMaster"
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)
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// withMaster adds the context value that master DB should be selected for this request.
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func withMaster(ctx context.Context) context.Context {
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return context.WithValue(ctx, storeContextKey(useMaster), true)
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}
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// hasMaster is a helper function to check whether master DB should be selected or not.
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func hasMaster(ctx context.Context) bool {
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if v := ctx.Value(storeContextKey(useMaster)); v != nil {
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if res, ok := v.(bool); ok && res {
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return true
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}
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}
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return false
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}
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