Use UuidProvider based on UUIDv7

[valery-shinkevich]

Right now, Jmix uses a UuidProvider that generates randomly based UUIDs. This is sufficient for small applications, but for applications where there is a lot of data and UUID is used as primary keys, this causes poor index locality.

Various modifications of UUID generator have been used for a long time to solve this problem. They are all somewhat similar and use time-based UUID generation.

Not so long ago, new UUID formats were introduced, in particular UUIDv7. New UUID Formats - draft This is one of the solutions of poor index locality and already has many implementations for databases and programming languages. You can also read a lot of articles on this topic, for example: Goodbye integers. Hello UUIDv7! Спецификация уникальных идентификаторов UUIDv7 для ключей баз данных и распределенных систем по новому стандарту RFC9562

However, this solution is not suitable for all databases, as far as I know at the moment (I would be glad to be mistaken), MS SQL Server uses a slightly different byte order for storing GUIDs. Therefore, it would be nice to use the ability to set the generator in the application configuration.

[valery-shinkevich]

I found a good implementation of various UUID versions and made a small test of ordering of different types of UUIDv7. Add uuid7 and test (WIP)

[knstvk]

Thank you for suggestion, we'll consider changing the default UUID provider to use UUIDv7 in the next feature release.

Currently you can use a custom provider for attributes annotated with @JmixGeneratedValue if you define an appropriate EntityInitializer bean in your project, for example:

package com.company.onboarding;

import io.jmix.core.EntityInitializer;
import io.jmix.core.JmixOrder;
import io.jmix.core.Metadata;
import io.jmix.core.UuidProvider;
import io.jmix.core.entity.EntityValues;
import io.jmix.core.entity.annotation.JmixGeneratedValue;
import io.jmix.core.metamodel.model.MetaClass;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;

import java.util.UUID;

@Component
public class MyGeneratedIdEntityInitializer implements EntityInitializer, Ordered {

    private final Metadata metadata;

    public MyGeneratedIdEntityInitializer(Metadata metadata) {
        this.metadata = metadata;
    }

    @Override
    public void initEntity(Object entity) {
        MetaClass metaClass = metadata.getClass(entity);
        metaClass.getProperties().stream()
                .filter(property -> property.getRange().isDatatype()
                        && property.getRange().asDatatype().getJavaClass().equals(UUID.class)
                        && property.getAnnotations().get(JmixGeneratedValue.class.getName()) != null)
                .forEach(property -> {
                    if (EntityValues.getValue(entity, property.getName()) == null) {
                        UUID uuid = UuidProvider.createUuid(); // use your UUID provider
                        EntityValues.setValue(entity, property.getName(), uuid);
                    }
                });
    }

    @Override
    public int getOrder() {
        return JmixOrder.HIGHEST_PRECEDENCE - 10;
    }
}

Pay attention to the order - it must be a lower number (higher precedence) than defined in the GeneratedIdEntityInitializer bean of the framework.