Comments - Why are almost all ROWS_EXAMINED values 0 in events_statements_* tables (performance_schema) !?
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Thank you for this information ... But somehow I still do not understand, why then I still do not see ROWS_EXAMINED for most (or on some servers ALL!) queries in the events_statements_summary_by_digest view? I mean, there i should have a summary of queries which have long been finished.
As an example, on a server I have for example an entry with a simple "SELECT ...." (well, I have hundred similar ones ... but this is just as an example) in events_statements_summary_by_digest which says which has a COUNT_STAR=1901867 (so, it was fired quite often) ... And the time period over which this data was collected spans about 10 days (FIRST_SEEN to LAST_SEEN). Now, I would expect, that such a query has seen "the end of the query" quite often ... and as such, it should have yielded a valid ROWS_EXAMINED value quite often (and thus contribute tu a meaningful summary). But instead, ROWS_EXAMINED=0!
And this is my main problem, that on some servers all ROWS_EXAMINED are equal 0 in the summary tables. Which makes it quite "useless" for any type of analysis (whereas I think, that this value could be one of the most interesting one ... if it worked as expected/hoped).
So, I can understand, that in a "snapshot" view (like PROCESSLIST or event_statemnts_current) the ROWS_EXAMINED might be empty ... but in the summary (where a lot of already finished stuff should be summed up), it does not makes much sense to me.
So, can you tell me, why even in all the summaries, the ROWS_EXAMINED is almost always 0 (even for many, simple "SELECT ..." queries, which should have yielded ROWS_EXAMINED quite often at the end of their execution)?