Re: BUFFER_LOCK_EXCLUSIVE is used in ginbuildempty().

Peter Geoghegan <pg(at)heroku(dot)com> writes:
> On Thu, Jul 17, 2014 at 7:47 AM, Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)com> wrote:
>> I don't understand the point of having these GIN_EXCLUSIVE / GIN_SHARED
>> symbols. It's not like we could do anything different than
>> BUFFER_LOCK_EXCLUSIVE etc instead. It there was a GinLockBuffer() it
>> might make more sense to have specialized symbols, but as it is it seems
>> pointless.

> It's a pattern common to the index AMs. I think it's kind of pointless
> myself, but as long as we're doing it we might as well be consistent.

I think that to the extent that these symbols are used in APIs above the
direct buffer-access layer, they are useful --- for example using
BT_READ/BT_WRITE in _bt_search calls seems like a useful increment of
readability. GIN seems to have less of that than some of the other AMs,
but I do see GIN_SHARE being used that way in some calls.

BTW, there's one direct usage of BUFFER_LOCK_EXCLUSIVE in the GIST code
as well, which should probably be replaced with GIST_EXCLUSIVE if we're
trying to be consistent.

regards, tom lane