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TabletManager: Check for context cancellation in loop within ChangeTabletType() #9842

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Mar 11, 2022
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TabletManager: Check for context cancellation in loop within ChangeTabletType() #9842

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e3052c4
Check for context cancellation in loop within ChangeTabletType()
rohit-nayak-ps Mar 8, 2022
3042b1e
Change error message
rohit-nayak-ps Mar 10, 2022
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3 changes: 3 additions & 0 deletions go/vt/vttablet/tabletmanager/tm_state.go
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,9 @@ func (ts *tmState) ChangeTabletType(ctx context.Context, tabletType topodatapb.T
// We must read the data again and verify whether the previous write succeeded or not.
// The only way to guarantee safety is to keep retrying read until we succeed
for {
if ctx.Err() != nil {
return ctx.Err()
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We had added the infinite loop intentionally, because we enter that code only if a topo write has failed. Once a topo write fails, the only way forward is to keep trying to read the topo server, because the information may or may not have been written.
However, I do understand the use case where they want to retry doing the same operation again, so we need to exit sometime and not wait indefinitely.

I just think we should wrap the returned error and explicitly say that the topo information might be different from the tablet information and that the user must call ChangeTabletType again to fix it.
Other than that, this looks good to me

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I just think we should wrap the returned error and explicitly say that the topo information might be different from the tablet information and that the user must call ChangeTabletType again to fix it.

Suggestions for the error message? return fmt.Errorf("context canceled updating tablet_type for %s in the topo, please retry", ts.tm.tabletAlias) ok?

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Yes I think that will work!

}
ti, errInReading := ts.tm.TopoServer.GetTablet(ctx, ts.tm.tabletAlias)
if errInReading != nil {
<-time.After(100 * time.Millisecond)
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