onstat -R command: Print LRU, FLRU, and MLRU queue information

Use the onstat -R command to display detailed information about the LRU queues, FLRU queues, and MLRU queues. For each queue, the onstat -R command displays the number of buffers in the queue and the number and percentage of buffers that have been modified.

For an in-depth discussion of the three types of queues, see LRU queues in the shared-memory chapter of the HCL OneDB™ Administrator's Guide.

Syntax:

onstat -R

Example output

Figure 2: onstat -R command output


        Buffer pool page size: 2048
        8 buffer LRU queue pairs              priority levels
    # f/m   pair total     % of    length       LOW      HIGH
     0 f        375     100.0%      375        375          0
     1 m                  0.0%        0          0          0
     2 f        375     100.0%      375        375          0
     3 m                  0.0%        0          0          0
     4 f        375     100.0%      375        375          0
     5 m                  0.0%        0          0          0
     6 F        375     100.0%      375        375          0
     7 m                  0.0%        0          0          0
     8 f        375     100.0%      375        375          0
     9 m                  0.0%        0          0          0
    10 f        375     100.0%      375        375          0
    11 m                  0.0%        0          0          0
    12 f        375     100.0%      375        375          0
    13 m                  0.0%        0          0          0
    14 f        375     100.0%      375        375          0
    15 m                  0.0%        0          0          0
    0 dirty, 3000 queued, 3000 total, 4096 hash buckets, 2048 buffer size
    start clean at  60.000% (of pair total) dirty, or 226 buffs dirty, stop at
      50.000%
    Buffer pool page size: 8192
        4 buffer LRU queue pairs              priority levels
    # f/m   pair total     % of    length       LOW      HIGH
     0 F        250     100.0%      250        250          0
     1 m                  0.0%        0          0          0
     2 f        250     100.0%      250        250          0
     3 m                  0.0%        0          0          0
     4 f        250     100.0%      250        250          0
     5 m                  0.0%        0          0          0
     6 f        250     100.0%      250        250          0
     7 m                  0.0%        0          0          0
    0 dirty, 1000 queued, 1000 total, 1024 hash buckets, 8192 buffer size
    start clean at  60.000% (of pair total) dirty, or 150 buffs dirty, stop at
      50.000%

Output description

Buffer pool page size

Is the page size of the buffer pool in bytes

#

Shows the queue number

Each LRU queue is composed of two subqueues: an FLRU queue and a MLRU queue. (For a definition of FLRU and MLRU queues, see LRU queues in the shared-memory chapter of the HCL OneDB Administrator's Guide.) Thus, queues 0 and 1 belong to the first LRU queue, queues 2 and 3 belong to the second LRU queue, and so on.

f/m

Identifies queue type

This field has four possible values:

f: Free LRU queue
In this context, free means not modified. Although nearly all the buffers in an LRU queue are available for use, the database server attempts to use buffers from the FLRU queue rather than the MLRU queue. (A modified buffer must be written to disk before the database server can use the buffer.)
F: Free LRU with fewest elements
The database server uses this estimate to determine where to put unmodified (free) buffers next.
m: MLRU queue
M: MLRU queue that a flusher is cleaning

length

Tracks the length of the queue measured in buffers

% of

Shows the percent of LRU queue that this subqueue composes

For example, suppose that an LRU queue has 50 buffers, with 30 of those buffers in the MLRU queue and 20 in the FLRU queue. The % of column would list percents of 60.00 and 40.00, respectively.

pair total

Provides the total number of buffers in this LRU queue

priority levels

Displays the priority levels:

LOW, MED_LOW, MED_HIGH,
HIGH

The onstat -R command also lists the priority levels.

Summary information follows the individual LRU queue information. You can interpret the summary information as follows:

dirty: Is the total number of buffers that have been modified in all LRU queues
queued: Is the total number of buffers in LRU queues
total: Is the total number of buffers
hash buckets: Is the number of hash buckets
buffer size: Is the size of each buffer
start clean: Is the value specified in the lru_max_dirty field of the BUFFERPOOL configuration parameter
stop at: Is the value specified in the lru_min_dirty field of the BUFFERPOOL configuration parameter
priority downgrades: Is the number of LRU queues downgraded to a lower priority.
priority upgrades: Is the number of LRU queues upgraded to a higher priority.