Undefined results when using ReadFrom with SCAN family commands

[Dishant18]

Bug Report

Current Behavior

We have observed that when using the ReadFrom setting with SCAN family of commands, the continuation requests (with cursor) is not guaranteed to go to the same node as the first request. Due to this behaviour, the results of SCAN family requests are undefined.

We have a master-replica Redis setup with sentinel-based discovery.

Input Code

Input Code

RedisURI redisURI = RedisURI.Builder.sentinel("sentinel-host").build();
RedisClient redisClient = RedisClient.create(redisURI);

StatefulRedisMasterReplicaConnection<byte[], byte[]> conn = MasterReplica.connect(redisClient, ByteArrayCodec.INSTANCE, redisURI);
conn.setReadFrom(ReadFrom.ANY);

byte[] key = getKey();
ScanArgs scanArgs = ScanArgs.Builder.limit(256);
ScanCursor cursor = ScanCursor.INITIAL;
MapScanCursor<byte[], byte[]> resp;
do {
            resp = conn.sync().hscan(key, cursor, scanArgs);
            cursor = ScanCursor.of(hscan.getCursor());
            // Convert and add the results to a map
} while (!resp.isFinished());

Expected behavior/code

SCAN family continuation requests need to be sticky to a Redis Node. When it is used in conjunction with ReadFrom, on every continuation request - a new node can be chosen - which seems like a bug.

Environment

• Lettuce version(s): 6.4.0.RELEASE
• Redis version: 7+

Additional Context

The same support is present for ClusterScanCursor. It maintains a nodeId and routes the next command to the same node. Any reason for not adding this in Master-replica setup?

[tishun]

Hey @Dishant18 , please allow for the team to catch up with some work after the holidays and we will get back to you.

[shikharid]

@mp911de not contributing anymore?
If it's an oversight, it's a bug which you only can quickly ack and we (me/ @Dishant18 ) might be able to submit a fix.
Less effort for the new team that maintains this and quicker tat for us.

We are writing hacky code at our end to get around this behaviour.

[tishun]

@mp911de is always welcome to contribute, but I see he is quite busy with the Spring backlog.

If you and your team have a suggestion how to fix this you are more than welcome to submit a PR.
I'd still have to go over it and verify your solution though, but it shouldn't take much time.

In any case, even if you do not come up with a PR, the team would get to this issue ASAP and let you know how we think we should proceed.

[Dishant18]

@tishun gentle nudge on this one : )

We are only waiting for you to acknowledge that this is a bug, and we'll submit a PR for this soon. TIA

[Dishant18]

@tishun gentle nudge again : )
Any updates here will be much appreciated. TIA

[tishun]

Hey, apologies for that, I plan to spend some time for this this Friday.