Re: 8.0.0beta3 duration logging patch

Ed L. wrote:
> The attached patch forces queryless duration log statements to be turned off
> in step with the log_statement directive. Without this patch, and with
> log_statement = 'mod' and log_duration = true, there is no way to silence
> SELECT query duration logging when quieting the logging of SELECT queries.
>
> Note this patch changes the semantics of log_duration from logging the
> duration of "every completed statement" to "every completed statement that
> satisfies log_statement directive". I argue this semantic change is
> justified given 1) the docs themselves recommend turning log_statement
> sufficiently up to be able to make this mapping, and 2) I can see it being
> quite common that folks only want to log queries (and durations) that
> change the database, while I fail to see the usefulness of queryless
> durations (and I'm trying to scratch my own itch with a small effort).
> It's possible someone else feels strongly about their queryless durations
> for reasons I cannot imagine. If so, then another more conservative
> approach may be in order.
>
> Note also this patch is independent of queries and durations logged due to
> the log_min_duration_statement directive. If, for example, log_statement =
> 'all', log_min_duration_statement = 1 (ms), and a SELECT query takes longer
> than 1ms, it's duration will be logged twice, with the 2nd log entry
> including the statement with the duration.

Let me tell you how log_duration used to work. You would turn on
log_pid, log_statement, and log_duration, and you would use pid to link
together the query and the duration. That was kind of hard so we added
log_min_duration_statement that when set to zero prints all statements
and their durations, but it does it _after_ the query has run. Now that
log_statement is not a boolean but rather has four possible values, it
isn't as clear that you turn on log_statement and log_duration at the
same time and have them synchronized.

Your issue brings up that the boolean API doesn't really work well, and
in fact highlights the fact that printing the duration as an independent
capability really made no sense at all. Perhaps your approach is the
proper solution --- to link them together.

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