[Info-vax] RX2800 sporadic disk I/O slowdowns

[Richard Jordan]

On 11/5/24 6:22 AM, abrsvc wrote:
> Note:  Global buffers can be an advantage, but are not used when dealing
> with duplicate secondary keys.  Those are handled in local buffers. I
> have seen drastic differences in performance when changing bucket sizes
> more with secondary keys that have many duplicates than with primary
> keyed access.  Hein has some tools that analyze the statistics of
> indexed files that report the number of I/Os per operation. High values
> here can indicate inefficient use of buckets or buckets that are too
> small forcing the use of more I/Os to retrieve buckets.  Increasing the
> bucket size can significantly reduce I/Os resulting in better overall
> stats.
> 
> This won't directly address the reported slowdown, but might be a
> trigger for it depending upon data locality.
> 
> Dan

Dan,
      Apparently the name of Hein's tools changed and I just found the 
one referred to in the presentation.  Will try it on backup copies of 
the file (on the backup server) and see what it says.

      We tested doing a plain convert on all of the files involved in 
this situation on the backup server, and that task may be doable one 
file per weekend, but if the tuning apps require changes that mean doing 
an unload/reload of the file, going to have t find out how long that 
takes; backup windows are tight and except for rare VMS upgrade days (or 
when we moved from the RX3600 to these new servers), downtime is very 
hard to get.