Database Management - Cache Parameters: Zope database cache.

Description

This view allows you to view Zope database cache statistics and set cache parameters. The Zope database cache operates by keeping recently used objects in memory to improve performance. A large cache improves object access speed, but increases memory usage. A small cache reduces memory usage but may slow down object access speed.

Information

Total number of objects in the database

Indicates the number of persistent objects in the Zope database. All of these objects are stored on disk, some of them are in memory too.

Total number of objects in memory from all caches

Indicates the number of objects which are currently cached in memory. This is a good indication of the amount of memory used by Zope.

Target number of objects in memory per cache

Indicates the target number of objects to have in each cache at any given time. Zope will allow the number of objects to grow above this number while processing a request, but will always reduce the level to this number at the end of each request.

This parameter is one factor affecting the amount of memory use by Zope. It controls the amount of memory used per cache, the other factor is the number of caches. In general, Zope uses one cache per worker thread (specified by the -t switch on the command line)

Total number of objects in each cache

This table displays one row for each object cache.

Number of objects in memory

This value should not stay larger than the configured target size for longer than one transaction.

Note that the total number at the bottom of this column should be the same as the figure in the top half of the page. It may be slightly different because there is a small time interval between the calculation of the two totals.

Number of ghost objects

Ghost objects are those which only have a tiny memory footprint because their full state has not been loaded. You generally do not need to worry about the number of ghost objects because they are so small.