Redis MULTI, connection pool and WS problem

Hi,

We came across an interesting situation when running our app which roughly has:

• an event loop that keeps calling recv_frame. On close or error we call set_keepalive to keep the redis connection in a pool.
• a function (called from within the event loop) that uses redis MULTI - EXEC to run multiple statements in a "transaction".

The issue is that sometimes the connection that get added to the pool is 'in the middle of a transaction' (we know this because, when the redis connection is reused a call to incrby for example returns QUEUED instead of the int).

It's a bit like as if the lua function that does MULTI - EXEC is preempted by the event loop before it can finish.

The redis function is very simple, just a MULTI...few INCR....an EXEC.

Maybe it's just me not understanding how lua-nginx concurrency model but I assumed that any lua function would be executed completely before any other function (i.e. the event loop cycle) could continue. Is that not the case?

The only other thing that I can think of is if the EXEC had to fail and leave the transaction still active. Is that a possibility? How to overcome that?

Thanks :)

Start by tracing the event-loop entry point around recv_frame and the connection-pool handoff through set_keepalive, then review the MULTI/EXEC sequence and its responses. Reproduce reuse of a connection during or after a transaction and determine whether the transaction can remain active; done means the failure path and a reliable way to prevent or detect it are documented.