artembilan/spring-integration — comment on commit 0858f4b7fba0e9a67c6841c95b45673cf1cb7ed6
File: spring-integration-jdbc/src/main/java/org/springframework/integration/jdbc/JdbcMessageStore.java line 416
By artembilan:

since Derby doesn't support locks we'll get '0' after DELETE_MESSAGE if we try to poll message in two transactions at the same time