Inconsistent reads support

[MTigra]

TL;DR This is a request to support inconsistent reads, i.e. reads that can be served from any node rather than just the leader (in a quorum or non-quorum manner).

This is a risky feature but may have some value in certain use cases.

Right now i see i can use "follower-proxy" configuration to make redisraft proxy any commands to leader. Also i see that it is possible to disable quorum-reads. Even if i turn off quorum-reads, it mandatory to send all requests to leader node. How can i configure, or maybe edit sources to make it possible to read from every nore, even if it is lack of consistency.

[yossigo]

There's currently no way to configure that.

When you disable quorum-reads, you risk reading stale data within the re-election interval because you may read from a demoted leader that does not yet know it was demoted.

What you're asking is a way to read from arbitrary nodes, which means there is practically NO guarantee about the data you read. For example, this could be a follower node that has just joined and did not get ANY data yet.

Can you describe your use case, and why do you think that would be useful?

[MTigra]

Absolutely right. In my use case i mostly want write actions to be consistent, but its not important for read actions.
In my case i use redis mostly as cache to get better performance when reading data, but i also store that data in another storage, so data anyway would be safe.
Read actions, even they return incorrect data in some time not a problem, because they anyway WILL return correct data in some time later.

Probably it is not very common use case.

[sjpotter]

this is supported via debug commands. i.e. in our integration tests we do

redisraft/tests/integration/test_sanity.py

Line 35 in 4d49063

assert r2.raft_debug_exec('get', 'key') == b'value'

i.e.

redisraft/tests/integration/sandbox.py

Lines 266 to 272 in 4d49063

	def raft_debug_exec(self, *cmd):
	"""
	Execute the specified Redis command through RAFT.DEBUG EXEC,
	so it executes locally and does not go through Raft interception.
	"""
	return self.client.execute_command('raft.debug', 'exec', *cmd)

I'm not sure if one would really want to do this in real life, but the support is already there for them to do it.

[fadidahanna]

JIRA ticket: https://redislabs.atlassian.net/browse/RR-318