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Database Administrator's Guide

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Flexible I/O Channel Usage

A configuration keyword permits more flexible usage of multiple I/O channels. Without this feature, the ctDUPCHANEL file mode bit enables a file to use NUMCHANEL simultaneous I/O channels, where NUMCHANEL is set at compile time, and has traditionally been set to two. For superfile hosts with ctDUPCHANEL, 2* NUMCHANEL I/O channels are established. Two new server configuration keywords are now available for this feature:

SET_FILE_CHANNELS <file name>#<nbr of I/O channels>

DEFAULT_CHANNELS <nbr of I/O channels>

  • SET_FILE_CHANNELS: Permits the number of I/O channels to be explicitly set for the named file regardless of whether or not the file mode, at open, includes ctDUPCHANEL. A value of one for the number of I/O channels effectively disables ctDUPCHANEL for the file. A value greater than one turns on DUPCHANEL and determines the number of I/O channels used. The number of I/O channels is not limited by the compile time NUMCHANEL value. You may have as many SET_FILE_CHANNELS entries as needed.
  • DEFAULT_CHANNELS: Changes the number of I/O channels assigned to a file with ctDUPCHANEL in its file mode at open, unless the file is in the SET_FILE_CHANNELS list. The default number of channels is not limited by the NUMCHANEL value.

Note: When ctFeatCHANNELS is enabled, multiple I/O channels are disabled for newly created files. The multiple I/O channels take affect only on an open file call. Also, depending on default number of I/O channels, a superfile host not in the SET_FILE_CHANNELS will use no more than 2 * NUMCHANEL I/O channels.