Thread: Re: [HACKERS] autovacuum does not start in HEAD

I wrote:
> I found that autovacuum launcher does not launch any workers in HEAD.

The attached autovacuum-fix.patch could fix the problem. I changed
to use 'greater or equal' instead of 'greater' at the decision of
next autovacuum target.

The point was in the resolution of timer; There is a platform that timer
has only a resolution of milliseconds. We initialize adl_next_worker with
current_time in rebuild_database_list(), but we could use again the same
value in do_start_worker(), because there is no measurable difference
in those low-resolution-platforms.


Another attached patch, autovacuum-debug.patch, is just for printf-debug.
I got the following logs without fix -- autovacuum never works.

# SELECT oid, datname FROM pg_database ORDER BY oid;
  oid  |  datname
-------+-----------
     1 | template1
 11494 | template0
 11495 | postgres
 16384 | bench
(4 rows)

# pgbench bench -s1 -c1 -t100000
[with configurations of autovacuum_naptime = 10s and log_min_messages = debug1]

LOG:  do_start_worker skip : 230863399.250000, 230863399.250000, 230863409.250000
LOG:  rebuild_database_list: db=11495, time=230863404.250000
LOG:  rebuild_database_list: db=16384, time=230863409.250000
DEBUG:  autovacuum: processing database "bench"
LOG:  do_start_worker skip : 230863404.250000, 230863404.250000, 230863414.250000
LOG:  do_start_worker skip : 230863404.250000, 230863409.250000, 230863414.250000
LOG:  rebuild_database_list: db=11495, time=230863409.250000
LOG:  rebuild_database_list: db=16384, time=230863414.250000
LOG:  do_start_worker skip : 230863409.250000, 230863409.250000, 230863419.250000
LOG:  do_start_worker skip : 230863409.250000, 230863414.250000, 230863419.250000
LOG:  rebuild_database_list: db=11495, time=230863414.250000
LOG:  rebuild_database_list: db=16384, time=230863419.250000
...
(no autovacuum activities forever)

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center

Your patch has been added to the PostgreSQL unapplied patches list at:

    http://momjian.postgresql.org/cgi-bin/pgpatches

It will be applied as soon as one of the PostgreSQL committers reviews
and approves it.

---------------------------------------------------------------------------


ITAGAKI Takahiro wrote:
> I wrote:
> > I found that autovacuum launcher does not launch any workers in HEAD.
>
> The attached autovacuum-fix.patch could fix the problem. I changed
> to use 'greater or equal' instead of 'greater' at the decision of
> next autovacuum target.
>
> The point was in the resolution of timer; There is a platform that timer
> has only a resolution of milliseconds. We initialize adl_next_worker with
> current_time in rebuild_database_list(), but we could use again the same
> value in do_start_worker(), because there is no measurable difference
> in those low-resolution-platforms.
>
>
> Another attached patch, autovacuum-debug.patch, is just for printf-debug.
> I got the following logs without fix -- autovacuum never works.
>
> # SELECT oid, datname FROM pg_database ORDER BY oid;
>   oid  |  datname
> -------+-----------
>      1 | template1
>  11494 | template0
>  11495 | postgres
>  16384 | bench
> (4 rows)
>
> # pgbench bench -s1 -c1 -t100000
> [with configurations of autovacuum_naptime = 10s and log_min_messages = debug1]
>
> LOG:  do_start_worker skip : 230863399.250000, 230863399.250000, 230863409.250000
> LOG:  rebuild_database_list: db=11495, time=230863404.250000
> LOG:  rebuild_database_list: db=16384, time=230863409.250000
> DEBUG:  autovacuum: processing database "bench"
> LOG:  do_start_worker skip : 230863404.250000, 230863404.250000, 230863414.250000
> LOG:  do_start_worker skip : 230863404.250000, 230863409.250000, 230863414.250000
> LOG:  rebuild_database_list: db=11495, time=230863409.250000
> LOG:  rebuild_database_list: db=16384, time=230863414.250000
> LOG:  do_start_worker skip : 230863409.250000, 230863409.250000, 230863419.250000
> LOG:  do_start_worker skip : 230863409.250000, 230863414.250000, 230863419.250000
> LOG:  rebuild_database_list: db=11495, time=230863414.250000
> LOG:  rebuild_database_list: db=16384, time=230863419.250000
> ...
> (no autovacuum activities forever)
>
> Regards,
> ---
> ITAGAKI Takahiro
> NTT Open Source Software Center
>

[ Attachment, skipping... ]

[ Attachment, skipping... ]

>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings

--
  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

ITAGAKI Takahiro wrote:
> I wrote:
> > I found that autovacuum launcher does not launch any workers in HEAD.
>
> The attached autovacuum-fix.patch could fix the problem. I changed
> to use 'greater or equal' instead of 'greater' at the decision of
> next autovacuum target.

I developed a different fix, which is possible due to the addition of
TimestampDifferenceExceeds to the TimestampTz API.  (Thanks Tom).

It continues to work for me here, but please confirm that it fixes the
bug you reported -- I don't have a low-resolution platform handy.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

ITAGAKI Takahiro wrote:
> I wrote:
> > I found that autovacuum launcher does not launch any workers in HEAD.
>
> The attached autovacuum-fix.patch could fix the problem. I changed
> to use 'greater or equal' instead of 'greater' at the decision of
> next autovacuum target.

I have committed a patch which might fix this issue in autovacuum.c rev 1.44.
Please retest.

--
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support