PSORT_NPROCS

The PSORT_NPROCS environment variable enables the database server to improve the performance of the parallel-process sorting package by allocating more threads for sorting.

PSORT_NPROCS does not necessarily improve sorting speed for Extended Parallel Server, because the database server sorts in parallel whether this environment variable is set or not.

Before the sorting package performs a parallel sort, make sure that the database server has enough memory for the sort.

It is recommended that you initially set PSORT_NPROCS to 2 when your computer has multiple CPUs. If subsequent CPU activity is lower than I/O activity, you can increase the value of PSORT_NPROCS.

If the PDQPRIORITY environment variable is not set, the database server allocates the minimum amount of memory to sorting. This minimum memory is insufficient to start even two sort threads. If you have not set PDQPRIORITY, check the available memory before you perform a large-scale sort (such as an index build) to make sure that you have enough memory.

Default Values for Detached Indexes

If the PSORT_NPROCS environment variable is set, the database server uses the specified number of sort threads as an upper limit for ordinary sorts. If PSORT_NPROCS is not set, parallel sorting does not take place. The database server uses one thread for the sort. If PSORT_NPROCS is set to 0, the database server uses three threads for the sort.

Default Values for Attached Indexes

If the PSORT_NPROCS environment variable is set, you get the specified number of sort threads for each fragment of the index that is being built.

If PSORT_NPROCS is not set, or if it is set to 0, you get two sort threads for each fragment of the index unless you have a single-CPU virtual processor. If you have a single-CPU virtual processor, you get one sort thread for each fragment of the index.

For additional information about the PSORT_NPROCS environment variable, see your IBM Informix: Administrator's Guide and your IBM Informix: Performance Guide.