Re: [HACKERS] GSoC 2017: weekly progress reports (week 4) and patch for hash index

On Mon, Mar 12, 2018 at 12:18 AM, Alexander Korotkov
<a(dot)korotkov(at)postgrespro(dot)ru> wrote:
> On Sat, Mar 3, 2018 at 2:53 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>
>> On Fri, Mar 2, 2018 at 9:27 AM, Thomas Munro
>> > If that is indeed a race, could it be fixed by
>> > calling PredicateLockPageSplit() at the start of _hash_splitbucket()
>> > instead?
>> >
>>
>> Yes, but I think it would be better if we call this once we are sure
>> that at least one tuple from the old bucket has been transferred
>> (consider if all tuples in the old bucket are dead).
>
>
> Is it really fair? For example, predicate lock can be held by session
> which queried some key, but didn't find any corresponding tuple.
> If we imagine this key should be in new bucket while all existing
> tuples would be left in old bucket. As I get, in this case no locks
> would be transferred since no tuples were moved to the new bucket.
> So, further insertion to the new bucket wouldn't conflict with session,
> which looked for non-existing key, while it should. Do it make sense?
>

Valid point, I think on split we should always transfer locks from old
bucket to new bucket.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com