On Thu, Apr 30, 2020 at 4:07 PM 邱宇航 <iam...@gmail.com> wrote: > > I noticed that in hot standby, XLOG_STANDBY_LOCK redo is sometimes block by > another query, and all the rest redo is blocked by this lock getting > operation, which is not good and often happed in my database, so the hot > standby will be left behind and master will store a lot of WAL which can’t be > purged. > > So here is the idea: > We can do XLOG_STANDBY_LOCK redo asynchronously, and the rest redo will > continue. >
Hmm, I don't think we can do this. The XLOG_STANDBY_LOCK WAL is used for AccessExclusiveLock on a Relation which means it is a lock for a DDL operation. If you skip processing the WAL for this lock, the behavior of queries running on standby will be unpredictable. Consider a case where on the master, the user has dropped the table <t1> and when it will replay such an operation on standby the concurrent queries on t1 will be blocked due to replay of XLOG_STANDBY_LOCK WAL and if you skip that WAL, the drop of table and query on the same table can happen simultaneously leading to unpredictable behavior. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
