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Subject: Re: UUID generators worth the effort?
Reply-To: users@openjpa.apache.org
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To: users@openjpa.apache.org
From: =?UTF-8?Q?Francesco_Chicchiricc=c3=b2?= <ilgrosso@apache.org>
Message-ID: <570B4BFC.4020601@apache.org>
Date: Mon, 11 Apr 2016 09:02:20 +0200
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Hi all,
I went further and built a sample POC [10] which mimics the essentials=20
from Syncope.

I have defined an UUIDGenerator implementing Seq (and relying on [3] for =

UUID generation), and declared it via

@SequenceGenerator(name =3D "uuid", sequenceName =3D=20
"net.tirasa.ilgrosso.uuidpoc.openjpa.UUIDGenerator()")

in the @MappedSuperclass of both JPA entities available, plus defined

     @Id
     @GeneratedValue(strategy =3D GenerationType.SEQUENCE, generator =3D =
"uuid")
     private UUID id;

in both entities.

I have also extended the H2Dictionary to support the native UUID type=20
(without such extension, the id column would have had type BLOB).

All this above seems to work - at least for the simple JUnit test case=20
provided; I have some questions, though:

1. I have experimented that UUIDGenerator is instantiated twice: would=20
it be possible to defined it as singleton - as it happens for OpenJPA's=20
UUIDType4HexSeq?

2. How would the @SequenceGenerator annotation translates to orm.xml?=20
I've attempted the bare translation but it did not work.

3. The extended logic I have put in my H2Dictionary looks quite poor for =

the general case - even though good enough for my specific use case:

     @Override
     public String getTypeName(final Column col) {
         return col.getType() =3D=3D Types.BLOB && (col.isPrimaryKey() ||=
=20
col.isForeignKey())
                 ? "UUID"
                 : super.getTypeName(col);
     }

How much difficult would be to make it proper, e.g. recognize when the=20
class field is java.util.UUID? I'll need such extension for MySQL,=20
MariaDB, PostgreSQL, MS SQL Server and Oracle dictionaries.

4. I am used to rely on openjpa-maven-plugin to generate the=20
database.sql file; how can I configure it to use my H2Dictionary, and=20
not the default?

Thanks for your support.
Regards.

On 04/04/2016 10:49, Francesco Chicchiricc=F2 wrote:
> Hi all,
> in Syncope we are currently discussing [1] the option to replace our=20
> table generators-based id strategy to something else, based on UUID,=20
> which seem to offer several advantages.
>
> I have found [2], but I would rather prefer to generated UUID values=20
> manually (via [3] which seems to offer better performance and more=20
> features than the standard JDK's).
>
> In order to do so, I would replace the current
>
>     @Id
>     private Long id;
>
>     public Long getKey() {
>         return id;
>     }
>
> in  [4], backed by [5], with something like as
>
> @Id
> private UUID id;
>
> public UUID getKey() {
>   synchronized(this) {
>     if (key =3D=3D null) {
>       key =3D ... // generate via JUG [3]
>     }
>   }
>   return key;
> }
>
> As Syncope supports several DBMSes, I would also like to empower the=20
> underlying capabilities for storing such values:
>
>  * UUID Type for PostgreSQL [6]
>  * UNIQUEIDENTIFIER for SQL Server [7]
>  * RAW(16) for Oracle [8]
>  * BINARY(16) with some optimizations for MySQL / MariaDB [9] or=20
> vanilla with H2
>
> Do you have any suggestion about:
>
>  (a) the way how I am planning to support UUID generation
>  (b) the cleanest way to support DBMS differences (extending the=20
> respective DB dictionaries?)
>
> TIA
> Regards.
>
> [1] http://markmail.org/message/fhdrwerdwdm3opdx
> [2]=20
> http://openjpa.apache.org/builds/2.4.1/apache-openjpa/docs/jpa_overview=
_meta_field.html#jpa_overview_meta_gen
> [3] https://github.com/cowtowncoder/java-uuid-generator
> [4]=20
> https://github.com/apache/syncope/blob/master/core/persistence-jpa/src/=
main/java/org/apache/syncope/core/persistence/jpa/entity/user/JPAUser.jav=
a
> [5]=20
> https://github.com/apache/syncope/blob/master/core/persistence-jpa/src/=
main/resources/META-INF/spring-orm.xml#L87-L94
> [6] http://www.postgresql.org/docs/9.3/static/datatype-uuid.html
> [7]=20
> http://wiki.ispirer.com/sqlways/sql-server/data-types/uniqueidentifier
> [8]=20
> http://docs.oracle.com/cd/B28359_01/server.111/b28286/functions175.htm#=
SQLRF51816
> [9] https://www.percona.com/blog/2014/12/19/store-uuid-optimized-way/
[10] https://github.com/ilgrosso/OpenJPAUUIDPOC

--=20
Francesco Chicchiricc=F2

Tirasa - Open Source Excellence
http://www.tirasa.net/

Involved at The Apache Software Foundation:
member, Syncope PMC chair, Cocoon PMC, Olingo PMC, CXF committer
http://home.apache.org/~ilgrosso/