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onstat -g rah Read-ahead Request Statistics

The onstat -g rah command displays the read-ahead request statistics. For more details about the Read Ahead changes read this PDF 

Read Ahead

# threads            4
# Requests           34679
# Continued          2048
# Memory Failures    0
Q depth              0
Last Thread Add      05/17/2013.14:50

Partition ReadAhead Statistics

           Buffer    Disk     Hit   Data          Index         Idx/Dat
Partnum    Reads     Reads    Ratio # Reqs  Eff   # Reqs  Eff   # Reqs  Eff
0x200003  2412176 587381  75     0       0     150499  67    0       0
Option Description
# 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
Q Depth Depth of request queue
Last Thread Add Date and time when the last read-ahead thread was added
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 data page read ahead requests.
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.

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