IncrStManAccessor.h

The Table system has one or more storage managers underneath. One of these possible storage managers is the IncrementalStMan. This storage manager uses a cache of buckets. The default cache size is defined when the IncrementalStMan object was constructed at the time the table was created.

Sometimes it can be useful to change the cache size. E.g. when the table is accessed in a random way, the hit rate may drop when the cache is too small. The class ROIncrStManAccessor makes it possible to change the cache size in a temporary way.
Furthermore this class makes it possible to show the cache size and to show the cache statistics.

Motivation

In principle a pointer to IncrementalStMan could be used. However, that would give access to all public functions. Furthermore it could not distinguish between read/write and readonly tables.

Example

This example shows how to set the cache size for the incremental storage manager with the name "ISMExample". The cache size is not persistent, i.e. when the same table is reopened at a later time, this cache size is not remembered.

  // Open a table.
  Table table("someName.data");
  // Set the cache size of its incremental storage manager ISMExample
  // to 5 buckets.
  ROIncrementalStManAccessor accessor(table, "ISMExample");
  accessor.setCacheSize (5);

Member Description

ROIncrementalStManAccessor (const Table& table, const String& dataManagerName)

Construct the object for the data manager in the table. An exception is thrown if the data manager type does not match the type of this ROIncrementalStManAccessor object.

~ROIncrementalStManAccessor()

ROIncrementalStManAccessor (const ROIncrementalStManAccessor& that)

Copy constructor (reference semantics).

ROIncrementalStManAccessor& operator= (const ROIncrementalStManAccessor& that)

Assignment (reference semantics).

void setCacheSize (uInt nbuckets)

Set the cache size (in buckets) to be used by the storage manager. The cache size given in this way is not persistent. Only the cache size given to the constructors of the incremental storage managers, is persistent.

uInt cacheSize() const

Get the cache size (in buckets).

void clearCache()

Clear the caches used by the hypercubes in this storage manager. It will flush the caches as needed and remove all buckets from them resulting in a possibly large drop in memory used.

void showCacheStatistics (ostream& os) const

Show the statistics for each cache used by this storage manager.