Re: Changing WAL Header to reduce contention during ReserveXLogInsertLocation()

Claudio Freire <klaussfreire@gmail.com> writes:
> On Sat, Dec 30, 2017 at 7:32 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> So we can't completely remove xl_prev field, without giving up some
>> functionality.

> Or, you can use the lower 16-bits of the previous record's CRC

Hmm ... that is an interesting idea, but I'm not sure it helps much
towards Simon's actual objective.  AIUI the core problem here is the
contention involved in retrieving the previous WAL record's address.
Changing things so that we need the previous record's CRC isn't really
gonna improve that --- if anything, it'll be worse, because the
record's address can (in principle) be known sooner than its CRC.

Still, if we were just looking to shave some bits off of WAL record
headers, it might be possible to do something with this idea.

                        regards, tom lane