tcl.config.flush Menu/TCL


Command tcl.config.flush Menu/TCL
Applicable release versions:
Category TCL (746)
Description enters the Update processor to show the flush parameters.
The flusher is a background process ("daemon") which is in charge of copying modified memory back to disk. This process is normally sleeping, until either the number of pages requiring to be copied back to disk reaches a predetermined level, or after a fixed time.

Activity of the flusher can be monitored by the "buffers" TCL command.

"Flush period (s)"
This is the period in seconds after which the flush process wakes up to see if any pages in memory needs to be written back to disk. If the system is busy at that time, the flush process goes back to sleep almost immediately, since writing data to disk would load the disk when the application might need to do some useful reads. If the system is quiescent, the flush process starts writing data back to disk until a user process needs the disk again. The lower the flush period, the more often the memory will be copied back to disk. An absolute minimum should be a few seconds and the maximum around 30 to 60 seconds. This number can be changed dynamically by the TCL command "set-flush".

"Size of write queue"
This number determines the threshold at which the flusher wakes up to copy modified pages back to disk. For most systems, a value of 256 to 512 is suitable. If the memory is really low (less than a few megabytes), this number can be reduced to around 32, which should be a minimum.
Syntax config flush {vmname}
Related flusher