Control the B-tree Scanner

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Control the B-tree Scanner

Control B-tree scanner:
 
|-- -C--+-----------------+-------------------------------------|
        +-start-----------+
        +-stop--count-----+
        +-kill--count-----+
        +-threshold--size-+
        +-high------------+
        '-low-------------'

Element	Purpose	Key Considerations
-C	Controls the B-tree scanner for cleaning indexes of deleted items	Additional Information: There is no limit to the number of threads that can run at one time. However, there is a limit of 128 threads that can be started at one time. If, for example, you wanted 150 threads to run, you could execute two commands: onmode -C 100 and onmode -C 50.
stop count kill count	Stops or kills the B-tree scanner threads	Additional Information: Either of these threads stops or kills the B-tree scanners. If a count you specify is higher than the number of threads currently running, the current number is assumed. If you do not specify a number, then a count of 1 is assumed.
threshold size	Sets the minimum number of deleted items an index must encounter before placing a priority or hot list	Additional Information: Once all indexes above the threshold are cleaned, then indexes below the threshold are added to the hot list. The default threshold is 500. onmode -C threshold -1 cleans every index in the database. onmode -C threshold 0 cleans every index that has a dirty_hit count greater than 0.
high	Sets the priority of all B-tree scanner threads that are running	Additional Information: This option sets the priority of the B-tree scanner threads to equal that of normal users.
low	Sets the priority of all B-tree scanner threads that are running	Additional Information: This option sets the priority of the B-tree scanner threads lower than that of normal users. This command allows the B-tree scanner to consume only spare system resources, ensuring that the threads will not use the CPU cycles of normal users. The default priority is low.

The B-tree scanner assigns a profile to each index, depending on the amount of extra work the index places on the server. From the index profiles, the B-tree scanner develops a hot list: btc_create_hot_list. The B-tree scanner keeps track of the number of times items in an index causes the server to do extra work and cleans that index first. The index causing the next highest amount of extra work will then be cleaned, and so on in descending order. The B-tree scanner allocates cleaning threads dynamically, which allows for configurable workloads.