Repository save killing performance CPU utilisation - multithreading

Question

In my spring boot application, I have a ThreadPoolExecutor with 100 fixed threads. I have configured datasource as:
#Bean
#Primary
public LocalContainerEntityManagerFactoryBean entityManager() throws IOException {
LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
em.setDataSource(dbDatasource());
em.setPackagesToScan(new String[]{"com.pkg"});
em.setPersistenceUnitName("dbEntityManager");
HibernatePersistenceProvider hibernatePersistenceProvider = new HibernatePersistenceProvider();
em.setPersistenceProvider( hibernatePersistenceProvider );
HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
em.setJpaVendorAdapter(vendorAdapter);
HashMap<String, Object> properties = new HashMap<>();
properties.put("hibernate.dialect", env.getProperty("hibernate.dialect"));
properties.put("hibernate.naming-strategy", env.getProperty("spring.jpa.hibernate.naming-strategy"));
properties.put("hibernate.show-sql", env.getProperty("jdbc.show-sql"));
properties.put("logging.level.org.hibernate.SQL", env.getProperty("logging.level.org.hibernate.SQL"));
properties.put("logging.level.org.hibernate.type", env.getProperty("logging.level.org.hibernate.type"));
em.setJpaPropertyMap(properties);
return em;
}
#Primary
#Bean
public DataSource dbDatasource() throws IOException {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(env.getProperty("spring.datasource.driverClassName"));
dataSource.setUrl(env.getProperty("spring.datasource.url"));
dataSource.setUsername(env.getProperty("spring.datasource.username"));
dataSource.setPassword("");
System.out.println("DATABASE:" + dataSource.getUrl() +" "+ dataSource.getUsername());
return dataSource;
}
#Primary
#Bean
public PlatformTransactionManager transactionManager() throws IOException{
JpaTransactionManager transactionManager = new JpaTransactionManager();
transactionManager.setEntityManagerFactory(entityManager().getObject());
return transactionManager;
}
repository.save(entity) (of JpaRepository) is one of the operations that happens in the thread. The first save takes about 222ms but as there is load I see time taken to save rises 50-100ms per request reaching upto 10seconds per save.
Also, my CPU utilization shoots up incredibly to about 90%.
Can someone please help understand what I am missing?