RPC PubSub/confirmTransaction is unreliable with confirmed/singleGossip

[ryoqun]

Problem

Clients currently don't have nice and reliable way to follow updates to given subset's accounts.

Usually, PRC PubSub is the most straightforward solution; but we have some reports PubSub and confirmTransaction misses updates when used with commitment=confirmed/singleGossip.

It seem that the root problem is that we don't reliably send subscription notifications for that commitment level.

Also, this might be related to this old issue: #9909

Proposed Solution

Debug and fix it.

At least, provide some actionable work-around as a documentation.

CC: @jstarry @CriesofCarrots

[carllin]

hmm @CriesofCarrots is it possible here: https://github.com/solana-labs/solana/blob/master/core/src/optimistically_confirmed_bank_tracker.rs#L115-L119 that the root bank is set, purges the optimistically confirmed bank from BankForks, and then this check returns false?

[CriesofCarrots]

@jstarry , when you have a chance, could you add some detail here from your research on this issue? I think you said the nodes in question were unhealthy and you were not able to reproduce this issue once they had been rebooted.

[CriesofCarrots]

Regarding question above, adding a counter to see how often this occurs: #15492

[CriesofCarrots]

I believe this was fixed in #19092

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