Summary:
The callback loop in InlineSkipList::MultiGet updated finger.prev_[0] as it walked forward through entries (e.g., merge operands). When the MultiGet batch contained duplicate user keys, the next lookup for the same key would find finger.prev_[0] pointing to an entry that sorts AFTER the lookup key in internal key order (because the lookup key has a high sequence number which sorts first), violating the FindSpliceForLevel precondition: before == head_ || KeyIsAfterNode(key, before).
Fix: stop updating finger.prev_[0] in the callback loop. Only finger.next_[0] needs advancing to track the walk-forward position. The prev_[0] from FindGreaterOrEqualWithFinger is always a valid lower bound for any subsequent key, whether it uses kMaxSequenceNumber or a snapshot sequence number.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14465
Reviewed By: xingbowang
Differential Revision: D96882549
Pulled By: anand1976
fbshipit-source-id: a733fa9d4f23f8b55a027c257a114c4cf35abe2b
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