BasicKV::PrefixLookup: I notice the founction may return one KV pair. it is designing for that or a bug?

[SYaoJun]

expection

if I insert five pairs:
"hello": 1,
"hey": 2,
"hi": 3,
"holy":4,
"haha": 5

the prefixlookup("he") should return 2 kv pairs:
"hello": 1,
"hey": 2,
but the current code maybe return one kv pair, or return all the ascscan KV pairs.

code

[zz-jason]

It's a bug, BasicKv hasn't been fully tested. Would you like to fix this issue?

[SYaoJun]

yes, I can follow the BasicKV::ScanAsc() function, which use a pessimistic method. Actually, I want to fix it based on optimistic method. But I don't know how to handle the situation when a leaf node need move to their neighbor leaf

[zz-jason]

When latch conflict happens (the page being scanned is modified by others at the same time), an optimistic scan needs to:

• retry from the beginning (or retry scanning from the upper bound key of the last unchanged page)
• clear all the previously scanned and buffered key values

The current API sends each scanned key value to a custom callback, which makes the retry hard to implement. The easiest way to correctly implement ScanDesc or ScanAsc is to use a pessimistic shared iterator.