How to avoid blocking input queue?

Developers
1

I split inserting operations into my DB into two parts like (not the real API, just to show the idea):

  • startInserting(dbKey: Text, value: Text): Nat (returns insertId)
  • finishInserting(insertId: Nat): (Text, Text) (returns dbKey + the partition of the DB where it is stored)

This split into two API calls instead of one is necessary, because the insert functionality of my multi-partition DB requires await (non-atomic operation). If I had just one API call insert, this would make impossible to check whether the operation succeed.

Now I have a map of max. 15 entries created by startInserting that keep information for finishInserting to finish insert operation.

The bug: Call it 15 times and further inserts are blocked. As a workaround I would allow anybody to call finishInserting even on insertId created by another user, but in this way, for the user who called startInserting the return value of finishInserting would be lost.

I can’t remove the limit on the maximum number of insert operations, as this would allow an attacker to overflow my memory by calling many startInserting without finishing them by finishInserting.

So I don’t know what to do.

A similar situation is met in invoice canister. I don’t remember how they solve the similar problem. I think they remove old created invoices in order to save memory, correct? Should I do the same? How many insertions should I allow in parallel? (is 15 a good number?) If old insertions are removed, then should I in TypeScript code repeat startInserting if necessary more than once?

I realize that my explanation is clumsy. Please ask questions to understand me.

2

A single insert can do an await internally and return to the user after that await completed with the result (success or not). The await alone cannot be the reason you need two calls. Do you have other reasons? Like, for example, do you want to hide latency or do you want to batch multiple inserts into one call to the downstream canister (which would prevent you from replying to them individually with their respective result)?

Do you have a way to abort the insertion after the first step? Say startInserting completed but finishInserting wasn’t called for the insertId and then you won’t to overwrite that insertId (for example in a circular buffer of length 15). Then is it ok to overwrite that insertId? Can you undo in the downstream canisters everything that startInserting already caused?

3

If await did not success, I have item inserted but the notification procedure not ran, that is an inconsistent program state.

I have no way to abort the insertion after the first step.

Whether I can you undo in the downstream canisters everything that startInserting already caused, requires further analysis and stress testing.