Re: proposal - queryid can be used as filter for auto_explain

Thanks, the changes look good to me, I only have some minor comments
about naming/grammar:

+
+static auto_explain_queryids *queryId_filter = NULL;
+

That queryId_filter mixed case name seems strange, maybe
queryid_filter would be better?

+ /*
+ * We expect small number of watched queryids, and then
+ * a linear seaching is the fastest. As an alternative
+ * we can sort the array of queryId, and we can search
+ * there by bisection.
+ */

The patch should do either of those, but I don't think this comment
should stay in it after that decision? Linear search seems to be the
simpler/better choice to me, unless the goal is to handle 32-64-or
more ids.

+ /* Try to allocate an auto_explain_extension_options object. */
+ allocsize = offsetof(auto_explain_queryids, queryId) +
+ sizeof(int64) * list_length(elemlist);

The type is auto_explain_queryids, auto_explain_extension_options
isn't mentioned anywhere else?

"allows to specify list of queryid" - maybe query IDs?
"Only plan of query with queryid" - same
"Only queries with queryId from list will be logged." - same issue,
maybe "Only queries with the listed IDs will be logged?"
"works together" - work together