database - 是什么导致只读副本上的数据成为 old_snapshot 并导致冲突？

Question

多次遇到（在 RDS Postgres 实例上）后：

ERROR: canceling statement due to conflict with recovery
Detail: User query might have needed to see row versions that must be removed

我跑了（在热备上）：

SELECT *
FROM pg_stat_database_conflicts;

并发现所有的冲突都与confl_snapshot

这在文档中解释为：

confl_snapshot：此数据库中由于旧快照而取消的查询数

什么可能导致此冲突（作为旧快照）？

如果有帮助，以下是一些相关设置（通过SHOW ALL ;在待机状态下运行）：

hot_standby: on
hot_standby_feedback: off
max_standby_archive_delay: 30s
max_standby_streaming_delay: 1h
name,setting
old_snapshot_threshold: -1
vacuum_defer_cleanup_age: 0
vacuum_freeze_min_age: 50000000
vacuum_freeze_table_age: 150000000
vacuum_multixact_freeze_min_age: 5000000
vacuum_multixact_freeze_table_age: 150000000
wal_level: replica
wal_receiver_status_interval: 10s
wal_receiver_timeout: 30s
wal_retrieve_retry_interval: 5s
wal_segment_size: 16MB
wal_sender_timeout: 30s
wal_writer_delay: 200ms

标签： databasepostgresqlamazon-rdsreplication