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Throttler: set timeouts on gRPC communication and on topo communication #14165

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Oct 3, 2023
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Throttler: set timeouts on gRPC communication and on topo communication #14165

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7 changes: 7 additions & 0 deletions go/vt/vttablet/tabletserver/throttle/throttler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -714,6 +714,10 @@ func (throttler *Throttler) Operate(ctx context.Context) {

func (throttler *Throttler) generateTabletHTTPProbeFunction(ctx context.Context, tmClient tmclient.TabletManagerClient, clusterName string, probe *mysql.Probe) (probeFunc func() *mysql.MySQLThrottleMetric) {
return func() *mysql.MySQLThrottleMetric {
// Some reasonable timeout, to ensure we release connections even if they're hanging (otherwise grpc-go keeps polling those connections forever)
ctx, cancel := context.WithTimeout(ctx, 4*mysqlCollectInterval)
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@deepthi deepthi Oct 3, 2023 •
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Now that I look at this again, this local variable hides the context that is being passed in. If you are passed in a long-lived context and you want to use a shorter one within the function, it should be named something else.
Which also brings up the question - what is being passed in here? Is it context.Background()? that is bad.

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Whoops, didn't notice this comment before merging.

The context being passed is not context.Backgound(). It is the context sent to Operate(). And this is also the reason why disable&enable the throttler fixes the issue: Disable() cancels the context, which runs all the way down to cancelling the connection!

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Hiding the original context is fine -- the only consumer of the context is the gRPC call.

defer cancel()

// Hit a tablet's `check-self` via HTTP, and convert its CheckResult JSON output into a MySQLThrottleMetric
mySQLThrottleMetric := mysql.NewMySQLThrottleMetric()
mySQLThrottleMetric.ClusterName = clusterName
Expand Down Expand Up @@ -872,6 +876,9 @@ func (throttler *Throttler) refreshMySQLInventory(ctx context.Context) error {
}
// The primary tablet is also in charge of collecting the shard's metrics
err := func() error {
ctx, cancel := context.WithTimeout(ctx, mysqlRefreshInterval)
defer cancel()

tabletAliases, err := throttler.ts.FindAllTabletAliasesInShard(ctx, throttler.keyspace, throttler.shard)
if err != nil {
return err
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