Some system parameters control memory usage in IBM InfoSphere CDC. For improved performance, if you are able to allocate more than the default value of 512 MB for the IBM InfoSphere CDC Java Virtual Machine, then you can adjust the disk resource system parameters to use the increased memory.
mirror_global_disk_quota_gb
Use this system parameter to globally set a disk quota (in GB) for all capture components including temporary files, transaction queues, and LOBs which are staged on the target before being applied. IBM InfoSphere CDC will manage disk space utilization across all components as required.
Most databases have a mechanism that allows you to roll back or undo changes to your database by storing uncommitted changes. Similarly, IBM InfoSphere CDC uses the disk quota controlled by this system parameter to store in scope change data that has not been committed in your database. Once the database transaction is committed, the disk space used by the transaction is released.
Note IBM InfoSphere CDC stores the data in memory to improve performance and will only persist the data to disk if memory is unavailable.
The default setting of this system parameter is such that the product will only stop replicating after this disk quota exhausts all available disk space on your system. If you would prefer IBM InfoSphere CDC to stop replicating after it uses a specific amount of disk space, you can set the value with this system parameter.
Applies to: Source and Target
Default setting: 9223372036854775807
Maximum setting: 9223372036854775807
Minimum setting: 1
mirror_memory_txqueue_total_mb
This system parameter controls the amount of memory used to stage data on the source. For optimal performance, this system parameter should be large enough to hold the largest amount of uncommited data that will ever exist in the source database.
Applies to: Source
Default setting: 15 Megabytes
mirror_memory_txqueue_each_mb
This system parameter controls the amount of memory used to stage data on the source. For optimal performance, this system parameter should be large enough to hold the data for the largest transactions that occur on the source.
Applies to: Source
Default setting: 3 Megabytes
global_memory_lob_cache_mb
This system parameter controls the amount of memory that will be used to stage LOB values on the target. For optimal performance, this value should be large enough to hold the entire data for the largest LOB values that will be replicated.
This system parameter controls the ability of IBM InfoSphere CDC’s log scraping to take advantage of multiple processors. The default setting is acceptable for most situations. You can increase this value for highly scalable environments.
Applies to: Source
Default setting: 100 entries
Minimum setting: 100 entries
staging_store_can_run_independently
Use this system parameter to determine if subscriptions will exclusively use the IBM InfoSphere CDC staging store to accumulate change data or if they will be allowed to use independent log readers and log parsers to receive data directly from the database logs.
Set this parameter to one of the following values:
▪true—Specifies that subscriptions can use either the staging store to accumulate change data or use independent log readers and log parsers to receive data directly from the database logs.
▪false—Specifies that subscriptions will use the IBM InfoSphere CDC staging store to accumulate change data.
Changes to this system parameter value will only take effect after the replication engine is restarted.
If you change the value from true to false, you will need to clear the staging store before starting replication.
Applies to: Source
Default setting: true
staging_store_disk_quota_gb
Use this system parameter to specify the maximum amount of disk space (in GB) that will be utilized by the IBM InfoSphere CDC staging store on your source system.