On 07/02/2013 05:32 AM, Victor Sergeyev wrote:
Hello All.
I have a question about the patch `Add unique constraint to FixedIp`
(see https://review.openstack.org/#/c/29364/), which is a part of
blueprint `Complete db unique key enforcement on all tables dbs`
(https://blueprints.launchpad.net/nova/+spec/db-enforce-unique-keys).
There is a discussion about fixed_ip_bulk_create() behavior in this
patch review. At the moment this function receives a list of fixed_ips
and tries to insert these IPs to database one-by-one. If
DBDuplicateEntry exception raised, the function raises an exception with
the first duplicate IP in exception message. The same is true for
floating_ip_bulk_create() function.
Currently we can get only one duplicate IP error message per request.
So, if we add 1000 IP addresses, including 100 duplicates, we have to
call this function 100 times to find out which IPs aren't unique.
A few ways of modifying of this function have been proposed:
1) we can try to add all IPs to database using a bulk insert. If one of
those IPs violates the unique constraint, the exception is raised
containing the first duplicate IP address, the transaction is rolled
back and no IPs are saved to DB.
This keeps current behavior, but is significantly faster when a large
number of rows are inserted (Oslo integrity error handling code should
be modified a bit to retrieve the duplicated value from an exception
message).
2) we can add all unique IPs to database and write duplicate IPs to log.
This is much slower, because we have to create a separate transaction
for each IP (as the first integrity error would cancel the current
transaction until ROLLBACK was emitted).
On the other hand, this allows us to save valid IPs to database and
provide the caller with a list of duplicate IPs.
3) we can try to add all IPs to database. All duplicate IPs are
collected. If there is at least one duplicate, no IPs are saved to
database, but the caller receives a list with all duplicate IPs.
(A separate transaction is needed for each IP. The rollback must be done
manually by issuing of DELETE FROM matching duplicate IPs).
Or option #4:
Do a single query before starting any transaction that finds the
intersection of inserted floating IPs with existing floating IPs. Let's
call that set A.
if len(A) > 0:
raise SomeException("Message with list of existing floating IPs")
else:
try:
session.begin()
execute single query to insert records.
session.commit()
except:
session.rollback()
That way you get a fail-fast scenario and the only time you have any
issues (i.e. a rollback) is the rare occasion when you have a matching
floating IP inserted into the database in between your original query to
get the intersection and when you issue the call to insert the records.
Best,
-jay
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