On 8/17/20 7:49 AM, Drouvot, Bertrand wrote:
Hi,
On 8/6/20 12:24 PM, Magnus Hagander wrote:
Hi,
On 7/27/20 4:57 PM, Dave Page wrote:
Hi
Hi hackers,
I've attached a patch to display individual query in the pg_stat_activity query field when multiple SQL statements are currently displayed.
Motivation:
When multiple statements are displayed then we don’t know which one is currently running.
I'm not sure I'd want that to happen, as it could make it much harder to track the activity back to a query in the application layer or server logs.
Perhaps a separate field could be added for the current statement, or a value to indicate what the current statement number in the query is?
Thanks for he feedback.
I like the idea of adding extra information without changing the current behavior.
A value to indicate what the current statement number is, would need parsing the query field by the user to get the individual statement.
I think the separate field makes sense (though it come with an extra memory price) as it will not change the existing behavior and would just provide extra information (without any extra parsing needed for the user).
Idle though without having considered it too much -- you might reduce the memory overhead by just storing a start/end offset into the combined query string instead of a copy of the query.
Good point, thanks for the feedback.
The new attached patch is making use of stmt_len and stmt_location (instead of a copy of the query).
That way the cost would only be paid when doing the reading of pg_stat_activity (by extracting the piece of the string), which I'd argue is done orders of magnitude fewer times than the query changes at least on busy systems.
The individual query extraction (making use of stmt_len and stmt_location) has been moved to pg_stat_get_activity() in the new attached patch (as opposed to pgstat_report_activity() in the previous patch version).
Care would have to be taken for the case of the current executing query actually being entirely past the end of the query string buffer of course, but I don't think that's too hard to define a useful behaviour for. (The user interface would stay the same, showing the actual string and thus not requiring the user to do any parsing)
As a proposal the new attached patch does not display the individual query if length + location is greater than pgstat_track_activity_query_size (anyway it could not, as the query field that might contain multiple statements is already <= pgstat_track_activity_query_size in pg_stat_get_activity()).
Bertrand
Attaching a new version as the previous one was not passing the Patch Tester anymore.
Bertrand
