Re: New function pg_stat_statements_reset_query() to reset statisticsof a specific query

On Tue, Sep 25, 2018 at 01:49:09PM +1000, Haribabu Kommi wrote:
> Thanks for the review.
> Fixed in the attached patch as per your suggestion.

Hmm.  I see a problem with the tests and the stability of what
pg_stat_statements_reset() can return.  Normally installcheck is
disabled in contrib/pg_stat_statements/Makefile but if you remove this
barrier and run the tests with a server loading the module in
shared_preload_libraries then things are not stable.  We don't have this
kind of instability on HEAD.  Some call to pg_stat_statements_reset()
system-wide is visibly missing.

+   if (!pgss || !pgss_hash)
+       ereport(ERROR,
+               (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+                errmsg("pg_stat_statements must be loaded via shared_preload_libraries")));
This check can be within entry_reset().

+      the specified userid, dbid and queryid. Returns the total number of
+      statement statistics that are reset based on the specified input.
+      If any of the parameter is not specified, the default value NULL(invalid)
Missing some markups for the three field names here, as well as for NULL
which is a value.

I can buy the compatibility breakage with the return result of
pg_stat_statements_reset when specified without arguments.

Some nannyism: If all entries are removed and a new file needs to be
written, you could save a bit of indentation by returning immediately
when (num_entries != num_remove).