Resource Grant Manager

The Resource Grant Manager (RGM) is a database server component that coordinates the use of resources, where parallel branches are executed, and which queries to run if more than one query is in the queue.

The RGM dynamically allocates the following resources for PDQ queries and other parallel database operations:

• The amount of memory in the virtual portion of database server shared memory that the query can reserve

  The RGM uses configuration parameters, environment variables, and SQL statements to determine how to grant memory to a decision-support query.

• The number of parallel threads that can be started for each query

  The RGM uses the SQL operators that make up the query plan to determine the number of threads to start for a query.

  For join, group, and sort SQL operators, the RGM uses the following factors to determine the number of threads to start:

  • The values of configuration parameters (NUMCPUVPS, DS_TOTAL_MEMORY, DBSPACETEMP and so forth) that the database server administrator sets

    For more information on the parameters that you can set to affect parallelism, refer to your IBM Informix: Performance Guide.

  • The number of CPU VPs available
  • The availability of computer-system resources (CPUs, memory, and disk I/O)

  For scan and insert SQL operators, the RGM also uses the following factor to determine the number of scan and insert threads (disk I/O operators):

  • The number of fragments that the database operation accesses

For information about RGM, SQL operators, and fragmentation strategy guidelines to improve performance, refer to your IBM Informix: Performance Guide.