Clarification about READONLY errors inside a transaction

[luin]

Hi, I'm collaborating on a pull request in ioredis repo for handling READONLY errors inside a transaction. I think the behavior is inconsistent with the documentation so I'd just want to make sure here if it's a bug or something intentional.

Current behavior

Given two Redis servers (v5.0.6) A & B, A is the master and B is a read only replica (set up with replicaof A.host A.port), run the following commands in redis-cli against B:

B> multi
OK
B> set foo bar
(error) READONLY You can't write against a read only replica.
B> echo hi
QUEUED
B> exec
1) "hi"

EXEC command gives a partial result for the two command, which isn't expected.

Expected behavior

I think the whole transaction should be discarded.

In our documentation about transactions:

Before Redis 2.6.5 the behavior was to execute the transaction with just the subset of commands queued successfully in case the client called EXEC regardless of previous errors. The new behavior makes it much more simple to mix transactions with pipelining, so that the whole transaction can be sent at once, reading all the replies later at once.

It seems current behavior (that executing the transaction with the subset of commands queued successfully) is only normal for Redis < 2.6.5.

I checked the code and it seems READONLY is the only case that would fail without flagging the transaction. Is there any reasons behind this? If that's the case I think we should update the documentation accordingly.

https://github.com/antirez/redis/blob/1e16b9384d6aa3680ec5629fc0842ab53bf1655e/src/server.c#L3502-L3510

[WiFeng]

Before Redis 2.6.5 the behavior was to execute the transaction with just the subset of commands queued successfully in case the client called EXEC regardless of previous errors. The new behavior makes it much more simple to mix transactions with pipelining, so that the whole transaction can be sent at once, reading all the replies later at once.

I think that It is important to mix transaction with pipelining. It is a server side capability, so you also should use pipelining to send your all commands once.

The redis-cli is a simple redis client that does not use pipelining.

[alavers]

Hello @WiFeng! The same behavior is present with or without pipelining. I think what @luin is getting at is: why isn't flagTransaction being called in the linked code block.

[itamarhaber]

Hi @luin - this looks like an inconsistency indeed, @antirez @yossigo @soloestoy?

[antirez]

Hi, that's a bug. Fixing.