ID Generator
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contribute to the Hibernate open source.
Requirement:
1) Multiple UidGenerator streams (say a stream per table in DB)
2) High performance Requirement - Transaction spanning across public and
private network, end to end response time is 3 sec - Hence ID generation is
few m.sec
3) Unique identifier of type String / long / int
* Say for example a particular DB table may need a String as the ID
so the generator need to provide
Long.toString(long value);
* Other tables may need a long or int.
4) Supporting multiple databases
5) Handle Transaction.
* (eg)
* Not participate in Transaction (when this is running in a session
bean)
* Start new Transaction (when this is running in a session bean)
etc...
6) Use of high-low algorithm
7) Unique even in a multi-VM environment
hilo or seqhilo in Hibernate provides only a few out of the above 7
requirements. We need to have a new type that provides all the above.
Design:
Our generator will take a name as input (generatorName)
The generatorName parameter has to be a unique string, which allows
sequential blocks of unique ids to be kept within each class/DB table. This
provides the ability to have multiple UidGenerator streams.
Internally, key (long, 8bytes) generation is achieved using a so-called
high-low algorithm, obtaining the high values (also known as "blocks") from
a single persistent source (the UidBlockPool). Within a given block, IDs are
generated in memory. The persistent store is accessed only during startup
and when a block is exhausted. Depending on application requirement the
latter occurrence can be very rare, if the block size is large enough.
Table Design :
TABLE ES_UIDBLOCKPOOL
NAME VARCHAR(50) NOT NULL
BLOCK_SIZE LONGINT
CURRENT_BLOCK LONGINT
Name is the generator name. (usually the name of the class that uses it)
The block size helps us to define custom block size. If sequential numbers
are needed, we could set the size to 1
Thus this makes it configurable. For each table we can set the custom block
size.
Current Block will have the current value for the Block for that particular
generator name.
The IDs are guaranteed to be unique even in a multi-VM environment, as long
as the persistent store is shared. IDs are not guaranteed to be sequential.
The generator provides unique ID that are either String or long or int based
on the request.
This could be configured in the same way as the existing ID generator in
Hibernate.
Advantages:
* Custom block size could be set. So could be used as sequence
generator also.
* It has all the features that we have in Increment, Sequence, Hilo in
Hibernate.
* Multiple ID Streams
* High performance
Regards,
P. Mukund.
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