Re: [HACKERS] GSoC 2017: weekly progress reports (week 6)

On 09/04/18 18:21, Andrey Borodin wrote:
>
>> 9 апр. 2018 г., в 19:50, Teodor Sigaev <teodor(at)sigaev(dot)ru>
>> написал(а):
>>>
>>> 3. Why do we *not* lock the entry leaf page, if there is no
>>> match? We still need a lock to remember that we probed for that
>>> value and there was no match, so that we conflict with a tuple
>>> that might be inserted later. At least #3 is a bug. The attached
>>> patch adds an isolation test that demonstrates it. #1 and #2 are
>>> weird, and cause unnecessary locking, so I think we should fix
>>> those too, even if they don't lead to incorrect results.
>>
>> I can't find a hole here. Agree.
> Please correct me if I'm wrong. Let's say we have posting trees for
> word A and word B. We are looking for a document that contains both.
> We will read through all posting tree of A, but only through some
> segments of B. If we will not find anything in B, we have to lock
> only segments where we actually were looking, not all the posting
> tree of B.

True, that works. It was not clear from the code or comments that that
was intended. I'm not sure if that's worthwhile, compared to locking
just the posting tree root block. I'll let Teodor decide..

> BTW I do not think that we lock ranges. We lock possibility of
> appearance of tuples that we might find. Ranges are shortcuts for
> places where we were looking.. That's how I understand, chances are
> I'm missing something.

Yeah, that's one way of thinking about it.

- Heikki