Re: COPY FREEZE and setting PD_ALL_VISIBLE/visibility map bits

Thanks. These patches seem to resolve the TOAST table issue, freezing it
as expected. I think the code duplication is not an issue, but I wonder
why heap_insert uses this condition:

/*
* ...
*
* No need to update the visibilitymap if it had all_frozen bit set
* before this insertion.
*/
if (all_frozen_set && ((vmstatus & VISIBILITYMAP_ALL_FROZEN) == 0))

while heap_multi_insert only does this:

if (all_frozen_set) { ... }

I haven't looked at the details, but shouldn't both do the same thing?

I've done some benchmarks, comparing master and patched version on a
bunch of combinations (logged/unlogged, no before-insert trigger,
trigger filtering everything/nothing). On master, the results are:

group copy vacuum
-----------------------------------------------
logged / no trigger 4672 162
logged / trigger (all) 4914 162
logged / trigger (none) 1219 11
unlogged / no trigger 4132 156
unlogged / trigger (all) 4292 156
unlogged / trigger (none) 1275 11

and patched looks like this:

group copy vacuum
-----------------------------------------------
logged / no trigger 4669 12
logged / trigger (all) 4874 12
logged / trigger (none) 1233 11
unlogged / no trigger 4054 11
unlogged / trigger (all) 4185 12
unlogged / trigger (none) 1222 10

This looks pretty nice - there are no regressions, just speedups in the
vacuum step. The SQL script used is attached.

However, I've also repeated the test counting all-frozen pages in both
the main table and TOAST table, and I get this:

master
======

select count(*) from pg_visibility((select reltoastrelid from pg_class
where relname = 't'));

count
--------
100000
(1 row)

select count(*) from pg_visibility((select reltoastrelid from pg_class
where relname = 't')) where not all_visible;

count
--------
100000
(1 row)

patched
=======

select count(*) from pg_visibility((select reltoastrelid from pg_class
where relname = 't'));

count
--------
100002
(1 row)

select count(*) from pg_visibility((select reltoastrelid from pg_class
where relname = 't')) where not all_visible;

count
--------
0
(1 row)

That is - all TOAST pages are frozen (as expected, which is good). But
now there are 100002 pages, not just 100000 pages. That is, we're now
creating 2 extra pages, for some reason. I recall Pavan reported similar
issue with every 32768-th page not being properly filled, but I'm not
sure if that's the same issue.

regards

--
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
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