SharePlex 8.6.6 - Administration Guide

Disable LOB Mapping

If you have PK/UK logging enabled on the source database (recommended to support more SharePlex features and faster processing), check the setting of the SP_OCT_ENABLE_LOBMAP parameter. This parameter controls whether or not SharePlex uses a LOB map when replicating tables that contain out-of-row LOB columns. The LOB map is used by the Capture process to map LOBIDs and rows when PK/UK logging is not enabled. LOB mapping is enabled by default. The SHAREPLEX_LOBMAP table stores these mappings.Transactions with numerous LOB operations can slow down Capture because it needs to maintain and refer to the mappings. If PK/UK logging is enabled on the database, you can disable LOB mapping by setting this parameter to 0.

To disable LOB mapping during active replication

1. Run sp_ctrl on the source system.

2. Set SP_OCT_ENABLE_LOBMAP to 0.

   sp_ctrl> set param SP_OCT_ENABLE_LOBMAP 0

3. Stop Capture.

   sp_ctrl> stop capture

4. Truncate the SHAREPLEX_LOBMAP table.

5. Restart Capture.

   sp_ctrl> start capture

Tune Capture on Exadata

The Capture process can be configured to use multiple capture threads for faster performance on an Exadata system. Capture reads directly from the logs on the Exadata ASM disks.

The SP_OCT_ASM_MULTI_OCI parameter controls the number of threads that Capture uses to read the redo logs.

The value set for this parameter must satisfy all of the following:

• greater than 1.
• an even divisor of the number of disks in the ASM disk group that stores the redo logs. For example, if there are 16 disks, the values of 2, 4, 8, and 16 are valid.
• not larger than the number of disks in the ASM disk group that stores the redo logs.

A large number of threads is not required, and performance actually diminishes with too many threads. The more threads, the more memory Capture requires.

Start with a small number of threads and monitor performance, then add threads if needed until you obtain an ideal balance between performance gain and memory usage. For example, if there are 16 disks, you could start with a value of 2.

To configure SharePlex for multi-threaded capture on Exadata

1. Run sp_ctrl.

2. Set the SP_OCT_ASM_MULTI_OCI parameter to the number of threads that you want Capture to use.

   sp_ctrl> set param SP_OCT_ASM_MULTI_OCI 3

3. Restart Capture.

Note: Capture automatically adjusts its buffer size to the value of the AU_SIZE parameter that is set for the disk group where the logs reside. This is the recommended buffer size for best performance and should not be changed. The SP_OCT_ASM_MULTI_OCI_BLOCK_SIZE parameter can override the default behavior if necessary.

Tune Checkpointing

Capture checkpoints it state to disk on a regular basis to support recovery. This information includes the log and location within that log of the most recently processes data. In a database environment where there are frequent log switches, a switch can occur before SharePlex writes its checkpoint. You can use the SP_OCT_CHECKPOINT_LOG parameter to ensure that Capture issues a checkpoint before a log switch.

The checkpoint is triggered when Capture lags a specified number of logs behind Oracle. For example, with the default of 2, Capture does a checkpoint when it falls 2 or more logs behind Oracle.

The range of permissible values for this parameter is from 2 (the default) to a value equal to the number of logs you are using. A value of 0 disables this feature.

Tune the Post process

This chapter contains instructions for improving the performance of the Post process. Because replicated data is applied through standard SQL mechanisms, the Post process provides the most potential for performance tuning.

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