Why write Information Schema plugins

The MySQL plugin API provides plugin developers with two ways of reporting status or statistical information to the user. Status variables were discussed in the previous chapter. They are best suited for reporting a small number of values that can be sorted into a fixed number of categories.

For example, we can use status variables to report the total number of disk syncs that our storage engine plugin has done, or the total number of different words that our full-text parser plugin has seen in the text. But we cannot use status variables to report, for example, a frequency distribution of words or word lengths—how many words of each length our full-text parser plugin has seen or (for a storage engine plugin) how many blocks each index takes and the block fill factor per index because the number of words or indexes may be very large, and because it is not known in advance, we cannot create a static array of all needed status variables.

Information Schema...