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Allows setting the cache strategy to be used for reading one file or a set of files. The notes below for a discussion of cache scanning.
Accepted Values
Value |
Effect |
Synonyms |
|---|---|---|
yes |
Enable the standard cache routines unless the read requires a cache page that is not already in cache. In that case, it limits each user to a maximum of 2 cache pages. |
y, true, on, 1 |
no |
The data cache buffer pages are managed using the default reuse scheme, which reassigns a cache page any time a read requires a page that is not already in cache. Default is no. |
n, false, off, 0 |
Example
To enable the cache scanning strategy:
<scancache>yes</scancache>
To disable cache scanning and use the default c-tree strategy:
<scancache>no</scancache>
Cache Scanning Strategy
The c-treeRTG <scancache> configuration option allows setting the cache strategy to be used for reading one file or a set of files. The <scancache> option is a boolean that is enabled with <scancache>yes</scancache>, or disabled with <scancache>no</scancache>.
If <scancache>no</scancache> is used, the data cache buffer pages are managed using c-tree's default reuse scheme, which reassigns a cache page anytime a read requires a page that is not already in cache. This strategy can allow a single user doing many reads from a single file to take over a large percentage of the total cache for that file.
If this option is enabled with <scancache>yes</scancache>, all the standard cache routines are used unless the read requires a cache page that is not already in cache. In that case, it limits each user to a maximum of 2 cache pages. The significance of this strategy is that a large set of data record read operations can be performed using only two cache pages with little or no decrease in performance compared to no restrictions on cache usage. Moreover, such restricted use may help other aspects of system performance since the bulk of data cache can be used for other files and/or other users. A large traversal of the data file by a single user will not replace other cache pages that may be useful to other users.
For more about this caching technique, see Scanner Cache in the FairCom DB Developer's Guide.
