Re: pgsql: Increase upper limit for vacuum_cleanup_index_scale_factor

On 26/06/2018 14.35, Alexander Korotkov wrote:
> Increase upper limit for vacuum_cleanup_index_scale_factor
>
> Upper limits for vacuum_cleanup_index_scale_factor GUC and reloption
> were initially set to 100.0 in 857f9c36. However, after further
> discussion, it appears that some users like to disable B-tree cleanup
> index scan completely (assuming there are no deleted pages).
>
> vacuum_cleanup_index_scale_factor is used barely to protect against
> stalled index statistics. And after detailed consideration it appears
> that risk of stalled index statistics is low. And it would be nice to
> allow advanced users setting higher values of
> vacuum_cleanup_index_scale_factor. So, set upper limit for these
> GUC and reloption to DBL_MAX.

UB Sanitizer points out that prev_num_heap_tuples is sometimes 0,
leading to division by 0 in
(info->num_heap_tuples - prev_num_heap_tuples) /
prev_num_heap_tuples >= cleanup_scale_factor)
which are currently lines 839-840 in nbtree.c.

Attaching my idea of a fix.