With the ubiquity of intelligent storage, the value of readahead in the Informix server is reduced and excessive readahead can be detrimental to performance. However, since the introduction of the AUTO_READAHEAD parameter and the associated changes to the readahead algorithms in the engine that include readahead of data that was not included in earlier versions of the engine, not all readahead details are exposed for analysis making it impossible to tune the AUTO_READAHEAD setting accurately.
Also while some details are available through the onstat -g rah output, not all values are exposed there either and none of that information is available through the SMI interface. Only the even more limited details exposed by onstat -p are available in sysmaster.
Why is it useful?
|Who would benefit from this IDEA?||Database administrators on large complex systems.|
How should it work?
Expose counts of all data read-ahead as well as counts of the number of readahead pages actually used/accessed either for reading or writing. It would be a nice-to-have to have exposed these values by pagesize/bufferpool in addition to overall values for the server instance.
|Priority Justification||Many many customers are configured to either perform excessive RA or insufficient RA and have no way to judge.|
|Customer Name||B&H Photo, Equifax, Material Logic, Walmart, The Home Depot, Cisco, all clients!|
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