How to control reindexing that results in high log send queue

Question

During reindexing using Ola's IndexOptimize stored procedure, the log send queues for remote asynchronous replicas can grow quite large if there are a lot of large index defrags, requiring gigantic transaction logs. There is an @Delay parameter in the script that can be used to insert a delay between each index operation, but it doesn't provide the ability to delay only when the log send queues are high.

A more intelligent throttling mechanism is required to control the log send queue sizes during heavy reindexing.

And yes, I know that reindexing isn't really necessary with our enterprise SSDs, but we do it to appease the third-party support organizations that will blame fragmentation for any performance issue.

Answer 1

Insert the following code into the IndexOptimize procedure to implement a wait that will allow the log send queues to flush before continuing. As written it will continue once there is less than 1 GB in the log send queues.

/* Pause until the log send queue is less than 1 GB */ 
WHILE ( (SELECT Sum(log_send_queue_size) 
         FROM   sys.dm_hadr_database_replica_states 
         WHERE  is_local = 0) > 1000000 ) 
  BEGIN 
      WAITFOR delay '00:01:00' 
  END 

This code needs to be placed immediately after the IF @Delay > 0 block in the procedure. With the current version of IndexOptimize, it would look like this:

IF @Delay > 0
BEGIN
    SET @CurrentDelay = DATEADD(ss,@Delay,'1900-01-01')
    WAITFOR DELAY @CurrentDelay
END

/* Pause until the log send queue is less than 1 GB */ 
WHILE ( (SELECT Sum(log_send_queue_size) 
         FROM   sys.dm_hadr_database_replica_states 
         WHERE  is_local = 0) > 1000000 ) 
  BEGIN 
      WAITFOR delay '00:01:00' 
  END