Re: GiST concurrency

Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
> Now I basically finished recovery for GiST (of course, it's need a hard testing)
> and go to concurrency. As it described in Kornaker, Mohan and Hellerstein's
> paper
> (http://www.sai.msu.su/~megera/postgres/gist/papers/concurrency/sigmod97-gist.pdf)
> it's need a way to get global LSN, in our case - XLogRecPtr of last changed
> page. As I understand, I can't use ProcLastRecPtr because it is one-process
> wide, I need value stored in shared memory.

If the method needs a truly global LSN, then it is broken --- the only
way you could have such a value and have it stay good long enough to do
anything with it is to block all other backends from inserting any new
WAL records. Which is the very antithesis of concurrency.

I think you probably misunderstood the paper. It looks to me like the
proposal in the paper is to use the LSN assigned to the WAL record that
represents a page split operation. Which you get from the XLogInsert
--- there's no need for an extra call.

regards, tom lane