Re: [HACKERS] GSoC 2017 : Proposal for predicate locking in gist index

On Thu, Jun 1, 2017 at 12:49 AM, Andrew Borodin <borodin@octonica.com> wrote:

> First, I just do not know, can VACUUM erase page with predicate lock?

For handling in btree, see:


https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/nbtree/nbtpage.c;h=f815fd40b20e98a88cb2fb5c71005ea125a459c9;hb=refs/heads/master#l1406

Note also this discussion:

https://www.postgresql.org/message-id/4D669122.80904@enterprisedb.com

It doesn't look like we ever got to the optimization Heikki
suggested in that post, so on rare occasions we could see a false
positive from this.  Perhaps we should give this another look while
we're in the AMs.

> Right now, GiST never deletes pages, as far as I know, so this
> question is only matter of future compatibility.

ok

> Second, when we are doing GiST inserts, we can encounter unfinished
> split. That's not a frequent situation, but still. Should we skip
> finishing split or should we add it to collision check too?

When a page is split, I think you need to call
PredicateLockPageSplit() before it gets to the point that an insert
to get to it.

--
Kevin Grittner
VMware vCenter Server
https://www.vmware.com/