Having the time of first occurence of a statement is very usefull for
it permits for exemple to retrieve the order of operations in some complex
cases (and thoses informations aren't taken by any third party collecting
tool, that will only be able to provide a time range of occurence).
I thougth that pgss rows where removed randomly when max rows was reached,
wouldn't having last_executed information permit a kind of LRU removal ?
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