A bug when using a prefix_extractor with a comparator.

[wqshr12345]

Note: Please use Issues only for bug reports. For questions, discussions, feature requests, etc. post to dev group: https://groups.google.com/forum/#!forum/rocksdb or https://www.facebook.com/groups/rocksdb.dev

I noticed in the comments about prefix_extractor in options.h, it is mentioned:

This means — all keys with the same prefix must be in a contiguous group by comparator order.
In the LevelIterator::Seek(), I noticed the following logic:

The meaning of this code is that during PrefixSeek, it can be pre-determined whether it is necessary to actually enter the next file for seeking based on the prefix value of the first key in the next file.
In fact,it is based on the assumption that "all keys with the same prefix must be in a contiguous group by comparator order".
However, I believe using user_comparator_.CompareWithoutTimestamp() is an incorrect usage. To compare "same prefix", it is more appropriate to use Slice's own Compare. The user comparator is not responsible for comparing prefixes.

[cbi42]

Hi - using Slice's own compare makes sense. Would you like to contribute a fix?

[wqshr12345]

@cbi42 Yes,I'd like to create a pr to fix it.

[wqshr12345]

@cbi42 I have create a pr #12862 to fix it.