卡夫卡-连接错误:无法获得有效的复制槽。

Question

我的应用程序中的Kafka debezium-postgres连接器抛出了以下错误：

org.apache.kafka.connect.errors.ConnectException: Unable to obtain valid replication slot. Make sure there are no long-running transactions running in parallel as they may hinder the allocation of the replication slot when starting this connector
    at io.debezium.connector.postgresql.connection.PostgresConnection.readReplicationSlotInfo(PostgresConnection.java:226)
    at io.debezium.connector.postgresql.connection.PostgresConnection.getReplicationSlotState(PostgresConnection.java:150)
    at io.debezium.connector.postgresql.PostgresConnectorTask.start(PostgresConnectorTask.java:98)
    at io.debezium.connector.common.BaseSourceTask.start(BaseSourceTask.java:49)
    at org.apache.kafka.connect.runtime.WorkerSourceTask.execute(WorkerSourceTask.java:198)
    at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:175)
    at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:219)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:834)

应用程序使用PostgreSQLVersion9.6.11，max_replication_slots的值为10。我可以看到数据库中的活动逻辑replication_slot为confirmed_flush_lsn = null，restart_lsn = 3/93043310，catalog_xmin = 202656，active = t，datoid = 16407，slot_type = logical，active_pid = 32183，plugin = wal2json，slot_name = slot1，数据库= db1 (我用虚拟值替换了槽名和db名称)。

根据我的理解，因为这里的逻辑复制槽的confirmed_flush_lsn = null会导致这个错误，因为它会阻止连接器找到这个插槽。

我如何解决这个问题，为什么confirmed_flush_lsn值将为空？

Answer 1

我通过重新启动由连接器引用的aws中的rds DB实例来修复它，之后，confirmed_flush_lsn的值被重置为类似于(restart_lsn = 3/93043310)的非空值。卡夫卡-连接能够找到replication_slot "slot1“的预期。连接器也被打开了。这暂时解决了我的问题，但首先我还是想了解如何将confirmed_flush_lsn =null设置为逻辑replication_slot。