Benchmarks from a 1-entity JPA (not Spring Data) app:

class          method  profile sample  beans   classes    heap  memory  median  mean  range
CompileBenchmark  main  demo   auto  139.000  7692.000  12.116  73.349  1.932  1.985  0.071
CompileBenchmark  main  first  auto  139.000  8521.000  13.259  82.449  2.218  2.261  0.057
SimpleBenchmark   main  demo   auto  139.000  8097.000  11.590  75.015  2.024  2.068  0.053
SimpleBenchmark   main  first  auto  139.000  8925.000  12.647  83.957  2.314  2.344  0.033

"Compile" uses compile-time entity code generation (via the Maven plugin). It’s about 100ms faster.

100 entities:

class          method  profile sample  beans  classes     heap  memory  median  mean  range
CompileBenchmark  main  demo   auto  139.000  7800.000  13.826  77.519  2.300  2.405  0.216
CompileBenchmark  main  first  auto  139.000  8628.000  17.058  88.630  2.595  2.676  0.106
SimpleBenchmark   main  demo   auto  139.000  8317.000  13.757  80.497  2.745  2.830  0.201
SimpleBenchmark   main  first  auto  139.000  9144.000  15.220  89.918  3.005  3.079  0.106

I.e. about 400ms faster. So wildly extrapolating from 2 data points, that’s about 3ms per entity.

Interestingly, you get another 100ms from setting hibernate.bytecode.provider=none explicitly:

class           method profile sample  beans  classes     heap  memory  median  mean  range
CompileBenchmark  main  demo   auto  139.000  7374.000  11.224  71.084  1.833  1.865  0.032
CompileBenchmark  main  first  auto  139.000  8237.000  12.898  80.952  2.147  2.201  0.055

Native Image

$ mvn clean install
$ CP=`java -jar $HOME/.m2/repository/org/springframework/boot/experimental/spring-boot-thin-launcher/1.0.22.RELEASE/spring-boot-thin-launcher-1.0.22.RELEASE-exec.jar --thin.archive=target/orm-0.0.1.BUILD-SNAPSHOT.jar --thin.classpath`
$ native-image --no-server -DremoveUnusedAutoconfig=true -Dio.netty.noUnsafe=true -H:+ReportExceptionStackTraces --no-fallback --allow-incomplete-classpath --report-unsupported-elements-at-runtime -H:Name=target/demo -cp target/classes/:$HOME/.m2/repository/org/springframework/spring-boot-graal-feature/0.5.0.BUILD-SNAPSHOT/spring-boot-graal-feature-0.5.0.BUILD-SNAPSHOT.jar:$CP app.main.SampleApplication
$ ./target/demo
Jun 28, 2019 7:35:28 AM com.fasterxml.jackson.databind.ext.Java7Support <clinit>
WARNING: Unable to load JDK7 types (annotations, java.nio.file.Path): no Java7 support added

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::

Jun 28, 2019 7:35:28 AM org.springframework.boot.StartupInfoLogger logStarting
INFO: Starting SampleApplication on tower with PID 20108 (started by dsyer in /home/dsyer/dev/demo/workspace/vanilla-orm)
Jun 28, 2019 7:35:28 AM org.springframework.boot.SpringApplication logStartupProfileInfo
...
Jun 28, 2019 7:35:28 AM org.springframework.boot.web.embedded.netty.NettyWebServer start
INFO: Netty started on port(s): 8080
Jun 28, 2019 7:35:28 AM org.springframework.boot.StartupInfoLogger logStarted
INFO: Started SampleApplication in 0.087 seconds (JVM running for 0.091)