onstat -g rah command: Print read-ahead request statistics

Use the onstat -g rah command to display information about read-ahead requests.

Read syntax diagramSkip visual syntax diagram
Syntax:

>>-onstat-- -g--rah--------------------------------------------><

Example output

Figure 1. onstat -g rah command output
Read Ahead

# Qs                 1
# threads            2         
# Requests           58690
# Continued		        0    
# Memory Failures    0         
Last Thread Add      04/06/2013.14:34
Way behind           0

Partition ReadAhead Statistics
   
          Buffer   Disk   Hit    Data       Index        Idx/Dat     Log/PageList Last Committed 
Partnum   Reads    Reads  Ratio  # Reqs Eff # Reqs  Eff  # Reqs  Eff # Pages Eff  # Reqs  Eff   # Resch 
0x200003  4312677  110    99     0      0   0       0    0       0    0      0     12906  100   0
0x300002  23740584 1427   99     0      0   0       0    0       0    0      0     6681   100   7
0x400002  17818942 966    99     0      0   0       0    0       0    0      0     25849  100   57    

Output description

Qs
Number of queues for read-ahead requests
# threads
Number of read-ahead threads
# Requests
Number of read-ahead requests
# Continued
Number of times a read-ahead request continued to occur
# Memory Failures
Number of failed requests because of insufficient memory
Last Thread Add
Date and time when the last read-ahead thread was added
Way behind
How many page list requests were dropped because the read-ahead daemon is too far behind
Partnum
Partition number
Buffer reads
Number of bufferpool and disk pages that were read
Disk Reads
Number of pages that were read from disk
Hit Ratio
Cache hit ratio for the partition
# Reqs
Number of read ahead requests. (There are 5 instances of this output field: for data, the index, index data, log pages, and last committed rows.)
Eff
Efficiency of the read-ahead requests. This is the ratio been the number of pages requested by read-ahead operations to the number of pages that were already cached and for which a read-ahead operations was not needed. Values are between 0 and 100. A higher number means that read ahead is beneficial. (There are 5 instances of this output field: for data, the index, index data, log pages, and last committed rows.)
Resch
The number of requests for last committed rows that are rescheduled because the updates to a multi-piece row are not complete.

Copyright© 2019 HCL Technologies Limited