Thread: Re: Trigger more frequent autovacuums of heavy insert tables

Re: Trigger more frequent autovacuums of heavy insert tables

From

Greg Sabino Mullane

Date:

25 October, 01:51:04

I really appreciate all the work to make vacuum better. Anything that helps our problem of autovacuum not scaling well for large tables is a win.

I'm not overly familiar with this part of the code base, but here are some questions/ideas:

+ /*
+ * Every block marked all-frozen in the VM must also be marked
+ * all-visible.
+ */
+ if (new_rel_allfrozen > new_rel_allvisible)
+ new_rel_allfrozen = new_rel_allvisible;
+

Maybe tweak either the comment, or the code, as I read that comment as meaning:

if (new_rel_allfrozen > new_rel_allvisible)

new_ral_allvisible = new_rel_allfrozen;

+ /*
+ * If we are modifying relallvisible manually, it is not clear
+ * what relallfrozen value would make sense. Therefore, set it to
+ * -1, or unknown. It will be updated the next time these fields
+ * are updated.
+ */
+ replaces[ncols] = Anum_pg_class_relallfrozen;
+ values[ncols] = Int32GetDatum(-1);

Do we need some extra checks later on when we are actually using this to prevent negative numbers in the calculations? It's only going to make pcnt_unfrozen something like 1.0001 but still might want to skip that.

In autovacuum.c, seems we could simplify some of the logic there to this?:

if (relpages > 0 && reltuples > 0) {

relallfrozen = classForm->relallfrozen;
relallvisible = classForm->relallvisible;

if (relallvisible > relpages)
relallvisible = relpages;

if (relallfrozen > relallvisible)
relallfrozen = relallvisible;

pcnt_unfrozen = 1 - ((float4) relallfrozen / relpages);

}
vacinsthresh = (float4) vac_ins_base_thresh + vac_ins_scale_factor * reltuples * pcnt_unfrozen;

Again, I'm not clear under what circumstances will relallvisible > relpages?

Cheers,

Greg