[cx-oracle-users] Oracle with sequence for primary key and that sequence out of sync

[Scott K. <sko...@gm...>]

Hello,

I am using version 5.1.2 of cx_Oracle with

>>> cx_Oracle.clientversion()
(11, 2, 0, 3, 0)

I am using it with SQLAlchemy 0.9.4 with Python 2.6.6 on RHEL 6.5.

My simple application queries an LDAP directory to find
particular records and then reflects the information into an
Oracle table. The application is designed to keep the database
table version of the information in sync with the LDAP
directory as the system of record.

Here is some pseudocode that shows the basic outline of what I
am doing:

class AdminGroup(Base):
    __tablename__ = 'admin_groups'

    id = Column(Integer, Sequence('seq_admin_groups_id'), primary_key = True)
    dn = Column(String)
    name = Column(String)
    display_name = Column(String)
    primary_mail = Column(String)

    def __repr__(self):
        return "<AdminGroup(dn='%s',name='%s',display_name='%s',primary_mail='%s')>"
% (
            self.dn, self.name, self.display_name, self.primary_mail)


db_engine = create_engine(...)
SessionClass = sessionmaker(bind = db_engine)

# loop every N minutes
    session = SessionClass()

    ldap_groups = ldap_connection.search_ext_s(...)

    for dn, attr_dict in ldap_groups:

        # see if group is represented in database table
        admin_group = session.query(AdminGroup).filter(AdminGroup.dn
== "%s" % dn).first()

        if admin_group:
            # group exists so see if any updates needed

        else:
            # create the group in the database table
            admin_group = AdminGroup(dn = dn, name = name, ...)
            session.add(admin_group)

    # done with all groups so commit and sleep until next iteration
    session.commit()

Note that the class AdminGroup() is written to use the
sequence seq_admin_groups_id to generate the primary key.

I created the sequence in the Oracle database using sqlplus
and the command:

CREATE SEQUENCE seq_admin_groups_id START WITH 1 INCREMENT BY 1;
COMMIT;

I then ran the Python code and it performed as I expected,
creating roughly 500 rows in the table. It continued to run
fine for a few days, creating and deleting rows now and then.

After a few days the code began throwing this exception:

2014-05-30 16:32:24,337 ERROR  Master: Caught database
exception while provisioning: (raised as a result of
Query-invoked autoflush; consider using a session.no_autoflush
block if this flush is occuring prematurely) (IntegrityError)
ORA-00001: unique constraint (MYSCHEMA.SYS_C0015706) violated
'INSERT INTO admin_groups (id, dn, name, display_name,
primary_mail) VALUES (seq_admin_groups_id.nextval, :dn, :name,
:display_name, :primary_mail) RETURNING admin_groups.id
INTO :ret_0' {'dn':
'cn=somename,ou=groups,dc=bc,dc=edu',
'primary_mail': 'som...@my...',
'display_name': 'somename', 'name':
'somename', 'ret_0': <cx_Oracle.NUMBER with value None>}

I investigated and found that the sequence seq_admin_groups_id
was now at the value 68 after having been used previously to
insert rows with IDs in the 500s.

I stopped the code and used sqlplus to change the sequence
back to a value in the high 500s. I then restarted the code
and the exception no longer occurred.

I am unable to explain how the sequence seq_admin_groups_id
went from in the 500s and working fine to suddenly being 68.

The only place in the Python code where the sequence is used
explicitly is in the definition of the AdminGroup() class.

I would be grateful for any insights on how the sequence might
have become out of sync or anything I can change in the code
to prevent it from happening again.

Thank you for your consideration.

Scott

P.S. I should add that I am using the connection
string

oracle+cx_oracle://user:password@(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=somehost)(PORT=1521)))(CONNECT_DATA=(SID=MYSID)))