Mark Rowell wrote:
To anyone on the list
Can you tell me how the SequenvceManagerHighLowImpl guarantees uniqueness of autoincremented Id's across JVMs -- I cant work out how it does it from the code....
(across JVMs using OJB) it use optimistic locking. (http://db.apache.org/ojb/faq.html#How to set up Optimistic Locking)
See SequenceManagerHighLowImpl#getSequence(...) method. If a new set of keys (e.g. next 20, from 221-240) was requested a HighLowSequence object was read from DB. This instance has a version number. If know another sequence manager instance (another thread or instance in different JVM) update the same HighLowSequence (same row in DB) the version number change. If we now try to store the requested HighLowSequence we will get an OptimisticLockingException.
regards, Armin
Thanks
Mark Rowell
-----Original Message-----
From: Mark Rowell [mailto:[EMAIL PROTECTED] Sent: 29 October 2003 13:38
To: 'OJB Users List'
Subject: RE: Auto incremented primary key and extents
Sorry -- I guess I am already using SequenceManagerHighLowImpl...(I should know this!).. So as it stands using RC4 I should be OK with multiple JVMs accessing the database using the HighLowImpl sequence manager.
Thanks
Mark
-----Original Message-----
From: Armin Waibel [mailto:[EMAIL PROTECTED] Sent: 29 October 2003 13:28
To: OJB Users List
Subject: Re: Auto incremented primary key and extents
Hi Mark,
Mark Rowell wrote:
Armin
Sorry for being thick -- I looked at the code again and understood and
tested it! As an aside, is there a sequence generator that will be unique across multiple JVMs
(and therefore OJB instances) accessing the database at the same time?
yep!
- SequenceManagerNextValImpl (use database based sequences, calling 'nextval' command). Unique across different JVM and different apps using sequences too.
- since SequenceManagerHighLowImpl use optimistic locking (>= rc3) this sequence manager implementation should be unique across JVM.
regards, Armin
Thanks
Mark
-----Original Message----- From: Armin Waibel [mailto:[EMAIL PROTECTED] Sent: 28 October 2003 20:08 To: OJB Users List Subject: Re: Auto incremented primary key and extents
Hi Mark,
Mark Rowell wrote:
Armin
On this note, with batch mode set to false, I decided to look into sequences in OJB. I currently use the default hi low sequence. I have an extent where the top level class is an interface And some concrete classes about 2 further levels down e.g.
TopLevelInterface + +---------------------+----------------+ Interface1 Interface2 Interface3 + + +------------+ +-----------+ Impl1 Impl2 Impl3 Impl4 etc
I often query things from the top level or one of the intermediate levels (Interface1 to 3 above). My question regarding sequences is that I have cleared out OJB_HL_SEQ as reocmmended in the documentation When changing repository/extents) and I notice that although the max ID
for
the extent with TopLevelInterface At the top is correct the sequence name appears to be Interface1. The
first
thing I did was save some instances of Impl1 and Impl2. Surely for
this to work next time the VM starts I would have to have the sequence name of ToplevelInterface so that the IDs are unique across the entire extent
(e.g.
from ToplevelInterface down)
The reason I say this is that if I start storing instances of Impl3 and 4 say, how will they get the right Sequence e.gf. Interface1 is not "visible" from Impl3 or 4 -- the only commonly visible interface is The top level one hence I would have expected the sequence to have this name.
I hope you can (or someone can) shed some light on my confusion.
doh! ;-) first, I don't know how your class-descriptors are defined. I will describe the best case scenario: Need sequence name for Impl3 autoincrement field Get TopLevel class for Impl3 --> TopLevelInterface Is TopLevelInterface is extent? --> then try to find first none null table name. Assume TopLevelInterface has extents Interface1, Interface2, Interface3 then OJB check all extents of Interface1,... for real class and its table name (search recursive the first none null table name - that's the reason for the note in the docs). The result for sequence name maybe SEQ_IMPL1_TABLE. Thus all real classes should get the same unique sequence name SEQ_IMPL1_TABLE.
Why not use name of the top level class as sequence name? Assume you
map the classes Fish and Mammal (no collective interface or base class) to one table. Then top level class name is equivalent to class names and you will end up with two different sequence names for the same table --> duplicate sequence keys.
I will be happy if you find a better solution :-)
By the way, if you don't trust the auto-generated sequence name for
such complex mappings, declare a sequence name in the field-descriptor of your classes.
regards, Armin
Regards,
Mark Rowell -----Original Message----- From: Armin Waibel [mailto:[EMAIL PROTECTED] Sent: 27 October 2003 12:50 To: OJB Users List Subject: Re: Auto incremented primary key and extents
Hi Mark,
Mark Rowell wrote:
Sorry
After looking at SequenceManaherHelper I know that the max id of sequence for extent is not...
More on the batch mode stuff -- I onlt just turned it on and got
these problems. RC4 has been working Prior to setting batch-mode="true" in the configuration.
hmm, AFAIK Oleg has fixed some bugs in conjunction with batch mode (since rc4). So your problems maybe a side-effect of the bugs in batch-mode.
regards, Armin
-----Original Message----- From: Mark Rowell [mailto:[EMAIL PROTECTED] Sent: 27 October 2003 12:25 To: 'OJB Users List' Subject: RE: Auto incremented primary key and extents
Armin
No the only thing I changed was OJB.properties.
One thing is that this problem happened during a run of my
application where some batch mode=true stuff Was used. Would this have an impact?
Is the sequence max id still stored in OJB_HL_SEQ?
Regards
Mark
-----Original Message----- From: Armin Waibel [mailto:[EMAIL PROTECTED] Sent: 27 October 2003 12:21 To: OJB Users List Subject: Re: Auto incremented primary key and extents
Hi Mark,
But as a follow on the extents are more than one level deep --
would > this > have an impact? No should not. Have a look in SequenceManagerHelper#getMaxForExtent
unique Over all tables in the extent? Have I misconfigured OJB on
upgrading
to RC4?
Did you change metadata on upgrading? Add new extents, change order of declaration?
regards, Armin
Mark Rowell wrote:
Sorry
But as a follow on the extents are more than one level deep -- would this have an impact?
Regards,
Mark Rowell
-----Original Message----- From: Mark Rowell [mailto:[EMAIL PROTECTED] Sent: 27 October 2003 11:30 To: '[EMAIL PROTECTED]' Subject: Auto incremented primary key and extents
Hi
I have an extent over 8 classes (and 8 corresponding tables) and I
have noticed that primary keys are now not unique over all tables -- e.g. when I store and instances of 2 different classes In different "leaves" of the extent I get the same ID in both tables. In RC1 I the autogenerated IDs were unique Over all tables in the extent? Have I misconfigured OJB on upgrading to RC4?
Regards,
Mark Rowell
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