Re: Reduce the size of PageFreeSpaceInfo on 64bit platform

ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> writes:
> Here is a revised patch to reduce memory usage during VACUUM,
> using FSMPageData (6 byte) instead of PageFreeSpaceInfo (8 or 16 bytes).

Applied, thanks.

> The keepable pages with freespace will extended to 21GB from 8GB with
> 16MB of default maintenance_work_mem.

AFAICS, maintenance_work_mem doesn't really have anything to do with
this; but it should reduce memory usage anyway if you've got large
relations and a large max_fsm_pages setting.

I'm a bit worried that the change may be pointless if FSM is rewritten
to not use dedicated shared memory, as I hope will happen for 8.4.
But we can always revert it if that happens.

regards, tom lane