Re: Locking B-tree leafs immediately in exclusive mode

On 5 June 2018 at 14:45, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> wrote:

> Currently _bt_search() always locks leaf buffer in shared mode (aka BT_READ),
> while caller can relock it later. However, I don't see what prevents
> _bt_search()
> from locking leaf immediately in exclusive mode (aka BT_WRITE) when required.
> When traversing downlink from non-leaf page of level 1 (lowest level of non-leaf
> pages just prior to leaf pages), we know that next page is going to be leaf. In
> this case, we can immediately lock next page in exclusive mode if required.
> For sure, it might happen that we didn't manage to exclusively lock leaf in this
> way when _bt_getroot() points us to leaf page. But this case could be handled
> in _bt_search() by relock. Please, find implementation of this approach in the
> attached patch.

It's a good idea. How does it perform with many duplicate entries?

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