On 9/20/11 11:45 AM, Kathey Marsden wrote:
On 9/20/2011 11:26 AM, Rick Hillegas wrote:
I have linked DERBY-5423 to DERBY-4437. This error can now appear as
a result of the work done on DERBY-4437. It is possible that the
error will go away if the default preallocation range for
sequences/identities is boosted from 20 values to something bigger
like 200. You might try re-running the test with this property setting:
derby.language.sequence.preallocator=200
If that does fix the problem, then we may want to consider whether 20
is too low a default for this setting.
Thank you Rick. Once an appropriate default is determined, I think it
would be good to update the release note to include a specific
reference to this error and actions to avoid it if it occurs on upgrade.
That sounds like a good idea.
Sadly, I think it is something that users are not likely to hit until
they are in a heavily loaded production environment. Is there a way
to acheive the prior behavior where there is not a risk of the error
occurring?
Here are some options:
1) It's easy to achieve the prior behavior by backing out the fix for
DERBY-4437. That would give up the concurrency boost provided by that
work. I believe the user experience of the prior behavior is that access
to the identity column goes down to single-threaded usage even at low
contention levels. This could be done for 10.8.2.
2) We could tackle the follow-on issue, DERBY-5295. That's a proposal to
make Derby tune the preallocation cache size in a smarter way. That
chunk of work is a mini-project and not a quick fix for 10.8.2.
Thanks,
-Rick
