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 to true
- 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