On Tuesday, July 1, 2014, john gale <john(at)smadness(dot)com> wrote:
>
> What does vacuum have to scan to be able to reclaim space, and how many
> times does it need to scan to finalize ?
>
> More specifically, my VACUUM VERBOSE <table> is taking a long time and
> seems to be rescanning the same indexes / fields multiple times without
> finishing.
>
vacuum can only memorize one dead tuple for every 6 bytes of
maintenance_work_mem. If there are more dead tuples than that, it needs to
make multiple passes over the indexes.
Increase maintenance_work_mem to improve the efficiency.
Cheers,
Jeff