Wednesday, March 16, 2005

An exercise in complexity....

Time for a grumble....

My plan was to take the API and expose it as an SE toolkit class. After looking at what it would take to do this I have come to the conclusion that the data structure definitions and API for reading the data are too complex.

The design is so abstract that it seems that reading meaningful data out of the log file is some obscure side effect of the code. You can read the data, but there is no guarantee that any specific item of data will be present. The accounting system has various options to send more or less data to the file, so it needs to be flexible, but the important thing is the meaning of the data being logged. I care about the semantic and informational content of the data source. What I get from exacct is "there are some tagged typed objects in this file". I can't consume the data without making assumptions about it, and the API doesn't embody those assumptions.

Some of the data being reported is useless (blocks in and blocks out are archaic measures that are always zero) and other stuff is missing - like the good microstate information on CPU wait, page-in wait etc.

I'm going to take the exdump.c code and turn it into a library that exports a sane and simple set of abstractions (like the data structures I defined in earlier posts).

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