Re: Minimum tuple threshold to decide last pass of VACUUM
| От | Simon Riggs |
|---|---|
| Тема | Re: Minimum tuple threshold to decide last pass of VACUUM |
| Дата | |
| Msg-id | CANP8+jKbC2HJ-44CAs4xY8KEZ2hbNQ_Or7Q01Go3_21A47v6Ng@mail.gmail.com обсуждение исходный текст |
| Ответ на | Minimum tuple threshold to decide last pass of VACUUM (Michael Paquier <michael.paquier@gmail.com>) |
| Ответы |
Re: Minimum tuple threshold to decide last pass of VACUUM
Re: Minimum tuple threshold to decide last pass of VACUUM |
| Список | pgsql-hackers |
On 2 August 2015 at 13:13, Michael Paquier <michael.paquier@gmail.com> wrote:
--
Hi all,
Commit 4046e58c (dated of 2001) has introduced the following comment
in vacuumlazy.c:
+ /* If any tuples need to be deleted, perform final vacuum cycle */
+ /* XXX put a threshold on min nuber of tuples here? */
+ if (vacrelstats->num_dead_tuples > 0)
In short, we may want to have a reloption to decide if we do or not
the last pass of VACUUM or not depending on a given number of
remaining tuples. Is this still something we would like to have?
I don't think we want a new user parameter, but we should have an internal limit with a heuristic, similar to how we decide whether to truncate.
I would suggest this internal logic...
* If its a VACUUM FREEZE then index_scan_threshold = 0, i.e. always scan if needed, since the user is requesting maximum vacuum
* For emergency anti-wraparound VACUUMs we shouldn't scan indexes at all, since they aren't critical path activities at that point
* For normal VACUUMs we should scan indexes only if (num_dead_tuples * 20) > (blocks to be scanned in any one index), which allows some index bloat but not much
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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