From: Ruben Perez (rubenperez038_at_[hidden])
Date: 2023-01-20 15:47:46
> No, The IO (read) is done by each individual async_exec call, so it
> can parse resp3 directly in their final storage without copies (i.e.
> the data structure passed by the user on the adapt function).
Out of curiosity, does having the parsing done in async_exec (vs. in async_run)
have to do with making no copies?
>
> > 2. If there are write errors in a request, it is async_run, and not
> > async_exec, the function that gets the error is async_run,
> > and not the individual requests queued by async_exec. Right?
>
> Correct.
What will happen with the request posted with async_exec? Will it
error with some special code, or will it just not complete until a
reconnection happens?
>
> A push has a fixed RESP3 type (the resp3 message starts with a >
> character). The heuristic you are referring to handles corner cases.
> Say I send a command that expects no response, but I do an error in
> its expected syntax: The server will communicate an error as a
> response, in this case I have no other alternative than passing it to
> async_receive, as it shouldn't cause the connection to be closed, it
> can be further used (a questionable thing but possible).
If I'm getting this correctly, if you make a mistake and async_exec
contains an invalid request, that error response is treated as a push.
Some additional questions:
a. Will async_exec complete successfully, or with an error?
b. Can you provide an example of the kind of mistake that would
cause this to happen?
c. What will happen if async_receive has not been called because no
server pushes are expected? Will it deadlock the connection?
> > 4. From what I've gathered, the protocol can be made full duplex
> > (you may write further requests while reading responses to
> > previously written requests),
>
> That is not how I understand it, I send a request and wait for the
> response. That is why pipeline is so important:
> https://redis.io/docs/manual/pipelining/. Otherwise why would it need
> pipelining?
What I mean: request batch A is written. While you are waiting for the response,
request batch B is enqueued using async_exec. I've understood that batch B
will wait until A's response has been fully read before it's written. Is there
a reason to make B wait, instead of writing it as soon as A's write is complete?
> The low-level API is there as a reference. I can't name any reason for
> using it instead of the connection, there are small exceptions which I
> will fix with time.
BTW, is the low-level API intended to be used by final users? As in,
will it be stable and maintained?
> Putting it in simple terms, I have observed situations where a push is
> in the middle of a response, that means the async_exec must be
> suspended and IO control passed to async_receive and then back to the
> suspended async_exec. This ping pong between async operations is
> complex to implement without async_run. I think there is a way
> though, we can talk more about that later.
Out of curiosity again, can you not deserialize the push from async_exec,
then notify (e.g. via a condition variable or similar) to async_receive?
>
> > 10. From what I've seen, all tests are integration tests, in that
> > they test with an actual Redis instance.
>
> The low_level.cpp and request.cpp are not integration tests. The
> others use a locally installed redis instance with the exception of
> the TLS test that uses db.occase.de:6380.
How do you handle parallel test executions? As in a CI running multiple
jobs in parallel. As an alternative, you may want to use a Docker container
for your CIs (which I've found to be much more practical). Let me know
if you go down this path, as I've got experience.
Regards,
Ruben.