tcl.blkio Verb: Access/TCL


Command tcl.blkio Verb: Access/TCL
Applicable release versions: AP/Unix, AP 6.2
Category TCL (746)
Description displays or sets the IO blocking factor, or number of frames read in one disk access during sequential file accesses. The setting is global for the whole system, and can be changed at any time.
The "blkio" command controls how many frames are read in one disk access by processes doing sequential file accesses, like the save or Access processors.

Without any argument, the current setting is displayed. If the mechanism is active, the following message is displayed:

IO blocking factor set to n frames.
indicates that sequential access will read "n" frames at each disk access.

If the mechanism is disabled, the following message is displayed:
IO blocking disabled.
indicates that the IO blocking mechanism is not active, and that frames are read one at a time.

The argument "factor" is the number of frames to be read at each disk access. '1' or 'off' disables the grouping of reads. The maximum number of frames that can be read is 64. See the general description of "blocked IO" for a detailed discussion of the blocked IO mechanism.

The blocking factor can also be set by adding the following statement in the virtual machine configuration file:
blkio n
where 'n' is the blocking factor.

The TCL "buffers" command allows monitoring the effect of blocking IO, by the "Frame faults" counter.
Syntax blkio {[factor|off]} {(option}
Options q Quiet. Do not display anything while setting the blocking factor.
IO blocking factor set to 2 frames.

   Display the current setting.

blkio 4 (q

   Set the blocking factor to 4 frames, suppressing the message.

blkio off
IO blocking disabled.

   Disable the mechanism.