Because Oracle GoldenGate replicates only committed transactions, it stores the operations of each transaction in a managed virtual-memory pool known as a cache until it receives either a commit or a rollback for that transaction. One global cache operates as a shared resource of an Extract or Replicat process. The Oracle GoldenGate cache manager takes advantage of the memory management functions of the operating system to ensure that Oracle GoldenGate processes work in a sustained and efficient manner. The CACHEMGR parameter controls the amount of virtual memory and temporary disk space that is available for caching uncommitted transaction data that is being processed by Oracle GoldenGate.

When a process starts, the cache manager checks the availability of resources for virtual memory, as shown in the following example:

CACHEMGR virtual memory values (may have been adjusted)CACHESIZE: 32GCACHEPAGEOUTSIZE (normal): 8M PROCESS VM AVAIL FROM OS (min): 63.97GCACHESIZEMAX (strict force to disk): 48G

If the current resources are not sufficient, a message like the following may be returned:

2013-11-11 14:16:22 WARNING OGG-01842 CACHESIZE PER DYNAMIC DETERMINATION (32G) LESS THAN RECOMMENDED: 64G (64bit system)vm found: 63.97GCheck swap space. Recommended swap/extract: 128G (64bit system).

If the system exhibits excessive paging and the performance of critical processes is affected, you can reduce the CACHESIZE option of the CACHEMGR. parameter. You can also control the maximum amount of disk space that can be allocated to the swap directory with the CACHEDIRECTORY option. For more information about CACHEMGR, see Parameters and Functions Reference for Oracle GoldenGate.