[Misc]: BlockHashType hash collision in v1

[WangErXiao]

Anything you want to discuss about vllm.

vllm/vllm/v1/core/kv_cache_utils.py

Line 13 in 4d29e91

"""Hash value of a block (int), the token IDs in the block, and extra keys.

I think this still has the potential for hash collisions. Using token IDs merely reduces the likelihood of such collisions. For example, in two sequences, if their previous block hashes are the same and the current block token IDs are also identical, a collision can still occur, albeit with a low probability.

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[WangErXiao]

@comaniac

[comaniac]

Yes the probability is not zero but this should (very) rarely happen, so don't have plan on it now. You're welcome to propose RFCs and I'll be happy to review.

[WangErXiao]

Yes the probability is not zero but this should (very) rarely happen, so don't have plan on it now. You're welcome to propose RFCs and I'll be happy to review.

I don’t have a very good idea at the moment. For now, we can simply add some explanations and clarifications.
#11847