Valid for: Currently supported for JMS
You can configure Post to split a large transaction into a series of smaller ones. This option can work around resource limits that affect large transactions, such as the number of row locks permitted per transaction.
To split a large transaction into smaller ones:
Use the target command to set the commit_frequency parameter.
target r.database [queue queuename] set resources commit_frequency=number_of_operations
This parameter specifies a maximum number of operations after which Post issues a commit. It can be any integer greater than 1.
Example:
target r.mydb queue q1 set resources commit_frequency=10000
You can tune the performance of Post by tuning the performance of the post queue.
Reduce queue contention
You can use the SharePlex queue contention reduction feature to ensure that shared memory is not swapped to disk when the post queue is becoming full. This feature is enabled by the SP_IMP_QUEUE_PAUSE parameter.
This parameter pauses the writing of data to the post queue when that queue contains the specified number of messages. Post stores queue messages in shared memory until it issues a checkpoint, after which it releases the data from memory.
If the post queue runs out of shared memory, the read and write functions will start incurring file IO to free up the memory buffers. By pausing the queue writing, this parameter helps Post maintain its performance by avoiding the need for disk storage and the resultant slowdown in IO.
Use the SP_IMP_QUEUE_RESUME parameter to set the number of messages at which Import resumes writing to the post queue. This parameter works in conjunction with SP_IMP_QUEUE_PAUSE. If the number of messages in the post queue is lower or equal to the value set with this parameter, Import resumes writing to the post queue.
To use this feature, both SP_IMP_QUEUE_PAUSE and SP_IMP_QUEUE_RESUME must be greater than zero, and SP_IMP_QUEUE_PAUSE must be greater than SP_IMP_QUEUE_RESUME.
Tune subqueue indexing
You can improve Post queue performance by enabling subqueue indexing to access the subqueue structures that represent a transaction session. A message "Subqueue index enabled queuename" is written to the Event Log for every Post queue for which this parameter is enabled.
To enable this feature, set the SP_QUE_USE_SUBQUE_INDEX parameter to 1. This parameter does not support VARRAYs. If you are replicating VARRAYs and this parameter is enabled, the parameter is ignored.
Hash-based horizontally partitioned replication uses a hash algorithm that is based on the rowid by default. You may be able to improve the processing of tables that use hash-based horizontally partitioned replication by switching the hash algorithm to one that is based on the block where the row resides.
Because changing the algorithm has the same effect as a routing change (the potential to switch partitions), you must reactivate the configuration file. The activation locks the tables that are affected by this change so that the hash change is applied when there are no open transactions. The locking eliminates the potential for out-of-sync conditions by preventing data that is processed under the new hashing algorithm from being posted before in-flight data that was processed under the old algorithm.
To switch to a block-based hash:
- Set the SP_OCF_HASH_BY_BLOCK parameter to 1.
- Reactivate the configuration file.
Recover Replication after Oracle Failover
This chapter contains instructions for recovering Oracle replication along with the database and applications during a failover in a high-availability environment. To support these procedures, SharePlex must be properly configured to support high availability. See Configure Replication to Maintain High Availability.
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