Re: four template0 databases after vacuum

Just a shot in the dark for a possible lead to follow down (sorry for top-posting):

 

Is there index corruption on system tables ?

 

(like, several index entries pointing to the one template0 row)

 

Karsten

 

 

Gesendet: Sonntag, 07. Februar 2016 um 03:43 Uhr
Von: "Kazuaki Fujikura" <fujya@fujya.com>
An: pgsql-general@postgresql.org
Betreff: [GENERAL] four template0 databases after vacuum



Hi there,

 

Version: 9.1.6 running since Dec, 2014

We have 3 different databases. 

 


[problem history/background]

 

Jan 10th, 2016:

The first problem was autovacuum issue.
- autovacuum could not finish successfully.

- I set autovacuum_freeze_max_age to 2 hundreds million.

- autovacuum immediately finished against the database which age was over 2 hundreds million.

- so, autovacuum did not go next database

- I then run "vacuumdb -az" and  run vacuum freeze analyze against template0 after setting datallowconn
totrue 

- I set datallowconn to false

 

============================================================

$ vacuumdb -az



$ psql template1

template1=# UPDATE pg_database SET datallowconn = TRUE where datname = 'template0';

UPDATE 1

template1=# \c template0

template0=# VACUUM FREEZE ANALYZE  ;

VACUUM

template0=# \c template1

template1=# UPDATE pg_database SET datallowconn = FALSE where datname = 'template0';

UPDATE 1

============================================================

 



- At this point, there is one template0 only

 

 



Jan 30th, 2016:
After three weeks, I again hit the same issue - autovacuum could not finish.

This time, the age did not reduce with manual vacuum.

I then run vacuum full to pg_database. The age of pg_database becomes minus value.

Then, autovacuum started again.

 

============================================================


target_db=# SELECT relname, age(relfrozenxid) FROM pg_class WHERE relkind = 'r' ;

                    relname            
       |    age     

------------------------------------------------+-----------

 pg_database                            
      | 219383067 

target_db=# VACUUM FREEZE ;

VACUUM

target_db=# SELECT relname, age(relfrozenxid) FROM pg_class WHERE relkind = 'r' ;

                    relname            
       |    age     

------------------------------------------------+-----------

 pg_database                            
      | 219387307 

target_db=# VACUUM FULL ;

VACUUM

                    relname            
       |    age     

------------------------------------------------+-----------

 pg_database                            
      | -1861408089 



============================================================

 

 

 


Yesterday:
 

I run the following command to run vacuum full to all pg_database.

Then, I run vacuum freeze analyze and vacuum  full to template0 after setting datallowconn.

 

============================================================

$ psql -lt | awk '{print $1}' | grep -v ^$ | grep -v ^\| | while read
line;do psql ${line} -c "VACUUM FULL pg_database;"; done 

VACUUM ....

 


$ psql template1

template1=# UPDATE pg_database SET datallowconn = TRUE where datname = 'template0';

UPDATE 1

template1=# \c template0

template0=# VACUUM FULL  ;

VACUUM

template0=# \c template1

template1=# UPDATE pg_database SET datallowconn = FALSE where datname = 'template0';

UPDATE 4
============================================================

 

***Then I HAVE FOUR template0 DATABASES***


 

 

 


[Current problems]
 

We now have three issues in our production.
 

1. It looks four template0 databases exist

2. Xid of template0 keeps growing

3. Can not freeze xid of template0

 

 

 


1. It looks four template0 databases exist

 

============================================================ 

$ psql -l | grep template0 

 template0                            
        | postgres   | UTF8             | C
      | C                 | =c/postgres  
      + 

 template0                            
        | postgres   | UTF8             | C
      | C                 | =c/postgres  
      + 

 template0                            
        | postgres   | UTF8             | C
      | C                 | =c/postgres  
      + 

 template0                            
        | postgres   | UTF8             | C
      | C                 | =c/postgres  
      + 

============================================================

 

These have same dataid.

 

============================================================ 

postgres=# SELECT datid, datname FROM pg_stat_database where datname = 'template0';

 datid |  datname  

-------+-----------

 12772 | template0

 12772 | template0

 12772 | template0

 12772 | template0

(4 rows)

============================================================

 

 

 


2. Xid of template0 keeps growing

 

============================================================

postgres=# SELECT datname, age(datfrozenxid) FROM pg_database order by age desc; 

                    datname            
       |    age     

------------------------------------------------+-----------

 template0                            
        | 198431852 

 template0                            
        | 198431852 

 template0                            
        | 198431852 

 template0                            
        |  50480024 

 template1                            
        |  45629585 

============================================================

 

At this moment, the maximum age value of all databases is template0.

The age value keeps growing.

 

One of 4 template0 is young (504080024). Other three template0s are still old.

 

 


 3. Can not freeze xid of template0

 

To reset xid of template0, I did vacuum full/ vacuum freeze to template0. But,

the age of three template0 did not change. Only of of 4 template0 had successfully

changed the age young.

 

============================================================

$ psql template1

template1=# UPDATE pg_database SET datallowconn = TRUE where datname = 'template0';

UPDATE 4

template1=# \c template0

template0=# VACUUM FREEZE ANALYZE  ;

VACUUM

template0=# VACUUM FULL  ;

VACUUM

template0=# \c template1

template1=# UPDATE pg_database SET datallowconn = FALSE where datname = 'template0';

UPDATE 4

============================================================

 

I run the commands above. But, I could not change the age of three template0 databases.

 


 


 

[My idea to fix this]

 

If I don't do anything about this, I think our production service will be down because it exceeds the limit of
xid.

 

I guess if I drop all template0 and create template0 again, then everything gets back normal.

But I am not quite sure if my approach is right.

 

I would appreciate any suggestion/comments.

 

Best regards,

Kazuaki Fujikura