select * from pg_extension where extname like '%repack%';
 extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition
---------+----------+--------------+----------------+------------+-----------+--------------
(0 rows)

"pg_repack";10;2200;f;"1.1.8";"";""

 select * from pg_extension where extname like '%repack%';
 extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition
---------+----------+--------------+----------------+------------+-----------+--------------
(0 rows)

"pg_repack";10;2200;f;"1.1.8";"";""

/usr/lib/postgresql/9.1/bin/psql -h 127.0.0.1 -p 5432 -U u.user -d MyDB -f /var/lib/postgresql/pg_repack-1.1.8/lib/uninstall_pg_repack.sql

$ /usr/lib/postgresql/9.1/bin/psql -f /var/lib/postgresql/pg_repack-1.1.8/lib/uninstall_pg_repack.sql             
psql:/var/lib/postgresql/pg_repack-1.1.8/lib/uninstall_pg_repack.sql:9:

postgres=# select user;
 current_user
--------------
 postgres
(1 row)

postgres=# select session_user;
 session_user
--------------
 postgres
(1 row)

postgres=# select * from pg_extension;
 extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition
---------+----------+--------------+----------------+------------+-----------+--------------
 plpgsql |       10 |           11 | f              | 1.0        |           |
(1 row)

postgres=# select datname, datdba from pg_database;
  datname   |  datdba
------------+----------
 template0  |       10
 postgres   |       10
 pgpool     | 35511673
 mydb        |    16385
 template1  |       10
 pb_opencms |    16387
(6 rows)

$ psql -d mydb
psql (9.1.9)
Type "help" for help.

mydb=# select * from pg_extension;
  extname  | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition
-----------+----------+--------------+----------------+------------+-----------+--------------
 plpgsql   |       10 |           11 | f              | 1.0        |           |
 lo        |       10 |         2200 | t              | 1.0        |           |
 pg_trgm   |       10 |         2200 | t              | 1.0        |           |
 pg_repack |       10 |         2200 | f              | 1.1.8      |           |
(4 rows)

$ /usr/lib/postgresql/9.1/bin/psql -d mydb -f /var/lib/postgresql/pg_repack-1.1.8/lib/uninstall_pg_repack.sql

psql:/var/lib/postgresql/pg_repack-1.1.8/lib/uninstall_pg_repack.sql:9:
ERROR:  cannot drop schema repack because extension pg_repack requires it
HINT:  You can drop extension pg_repack instead.

$ pgxn unload pg_repack
INFO: best version: pg_repack 1.1.8
The extension 'pg_repack' doesn't contain a control file:
will look for an SQL script to unload the objects.
Do you want to continue? [y/N] y

DROP EXTENSION pg_repack;

$ /usr/lib/postgresql/9.3/bin/pg_upgrade -b /usr/lib/postgresql/9.1/bin -B /usr/lib/postgresql/9.3/bin 
-d  /var/lib/postgresql/9.1/main/ -D /var/lib/postgresql/9.3/main/ -c
Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok
Checking for reg* system OID user data types                ok
Checking for contrib/isn with bigint-passing mismatch       ok
Checking for presence of required libraries                 ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok

*Clusters are compatible*

$ /usr/lib/postgresql/9.3/bin/pg_upgrade 
-b /usr/lib/postgresql/9.1/bin -B /usr/lib/postgresql/9.3/bin 
-d  /var/lib/postgresql/9.1/main/ -D /var/lib/postgresql/9.3/main/ -k

Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok
Checking for reg* system OID user data types                ok
Checking for contrib/isn with bigint-passing mismatch       ok
Creating dump of global objects                             ok
Creating dump of database schemas
                                                            ok
Checking for presence of required libraries                 ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok

If pg_upgrade fails after this point, you must re-initdb the
new cluster before continuing.

Performing Upgrade
------------------
Analyzing all rows in the new cluster                       ok
Freezing all rows on the new cluster                        ok
Deleting files from new pg_clog                             ok
Copying old pg_clog to new server                           ok
Setting next transaction ID for new cluster                 ok
Setting oldest multixact ID on new cluster                  ok
Resetting WAL archives                                      ok
Setting frozenxid counters in new cluster                   ok
Restoring global objects in the new cluster                 ok
Adding support functions to new cluster                     ok
Restoring database schemas in the new cluster
                                                            ok
Removing support functions from new cluster                 ok
Adding ".old" suffix to old global/pg_control               ok

If you want to start the old cluster, you will need to remove
the ".old" suffix from /var/lib/postgresql/9.1/main/global/pg_control.old.
Because "link" mode was used, the old cluster cannot be safely
started once the new cluster has been started.

Linking user relation files
                                                            ok
Setting next OID for new cluster                            ok
Sync data directory to disk                                 ok
Creating script to analyze new cluster                      ok
Creating script to delete old cluster                       ok

Upgrade Complete
----------------
Optimizer statistics are not transferred by pg_upgrade so,
once you start the new server, consider running:
    analyze_new_cluster.sh

Running this script will delete the old cluster's data files:
    delete_old_cluster.sh

/usr/lib/postgresql/9.3/bin/pg_ctl -D /var/lib/postgresql/9.3/main/ -l logfile start

Running this script will delete the old cluster's data files: delete_old_cluster.sh