如何在多个 Spring Boot 应用程序之间共享 H2 内存数据库？

Question

This is a different scenario than the other answered questions. I have one Spring boot application (app #1) that uses embedded H2 in-memory database and exposes it as a server. My second Spring boot application (app #2) connects to the H2 server from app #1 and that works correctly. I can store and retrieve data from H2. Now here is the problem. I have a third Spring boot (app #3) and it connects to the H2 server from app #1. The connection works but it (Issue #1) clears all the data that had been stored previously by app #2. After this, now both app #2 and #3 can store and retrieve its data and also each other's data. Now I terminate either app #2 or app #3 and (Issue #2) the remaining app cannot continue using the H2 in-memory database. Are issues #1 and #2 normal behavior? If not, how can I fix them? I want my H2 data to stay as long as app #1 (the H2 server) is running, even if other apps have been disconnected and I don't want my data cleared when new apps connect to the H2 server.

Answer 1

Found this in the docs here: https://h2database.com/html/features.html

By default, closing the last connection to a database closes the database. For an in-memory database, this means the content is lost. To keep the database open, add ;DB_CLOSE_DELAY=-1 to the database URL. To keep the content of an in-memory database as long as the virtual machine is alive, use jdbc:h2:mem:test;DB_CLOSE_DELAY=-1.

So I think your problem might be solved if you just set the db line in your application.properties file for app #1 to:

spring.datasource.url=jdbc:h2:mem:mydb;DB_CLOSE_DELAY=-1

Please let me know if this fixes your problem, as I'm very curious. Your description seems to suggest it's a bit more complicated than this...overlapping access from the two apps involved...but this sure sounds like the kind of parameter you're missing.

Answer 2

i did it this way , register multiple H2 servers in you spring configuration

@Bean(initMethod = "start", destroyMethod = "stop")
public Server h2Server1() throws SQLException {
    return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9080");
}

// Second App
@Bean(initMethod = "start", destroyMethod = "stop")
public Server h2Server2() throws SQLException {
    return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9081");
}

then while connecting to H2 used below config

for file based H2

url=jdbc:h2:tcp://localhost:9081/<path to H2>
username=sa
password=sa

for in-memory H2 database

url=jdbc:h2:tcp://localhost:9081/<H2 database name>
username=sa
password=sa