Re: Concurrent HOT Update interference

On Fri, May 10, 2013 at 5:23 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> Currently, when we access a buffer for a HOT update we check to see if
> its possible to get a cleanup lock so we can clean the buffer.
>
> Currently, UPDATEs and DELETEs pin buffers during the scan phase and
> then re-lock the buffer to update.
>
> So what we have is that multiple UPDATEs repeatedly accessing the same
> block will prevent each other from successful cleanup, since while one
> session is performing the update, the second session is pinning the
> block with an indexscan.

wait -- you can't acquire a cleanup lock if the buffer is pinned by at
least one other session?   yeah -- that would defeat HOT for many
important cases.  this should be pretty easy to demonstrate in
simulated testing.

merlin