Suppose that we're currently planning a query and, when that same
query was previously planned and executed, we learned something about
how a certain table within that query should be planned. We want to
take note when that same table is being planned during the current
planning cycle, but this is difficult to do, because the RTI of the
table from the previous plan won't necessarily be equal to the RTI
that we see during the current planning cycle. This is because each
subquery has a separate range table during planning, but these are
flattened into one range table when constructing the final plan,
changing RTIs.
Commit 8c49a484e8 allows us to match up
subqueries seen in the previous planning cycles with the subqueries
currently being planned just by comparing textual names, but that's
not quite enough to let us deduce anything about individual tables,
because we don't know where each subquery's range table appears in
the final, flattened range table.
To fix that, store a list of SubPlanRTInfo objects in the final
planned statement, each including the name of the subplan, the offset
at which it begins in the flattened range table, and whether or not
it was a dummy subplan -- if it was, some RTIs may have been dropped
from the final range table, but also there's no need to control how
a dummy subquery gets planned. The toplevel subquery has no name and
always begins at rtoffset 0, so we make no entry for it.
This commit teaches pg_overexplain's RANGE_TABLE option to make use
of this new data to display the subquery name for each range table
entry.
Reviewed-by: Lukas Fittl <lukas@fittl.com>
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Greg Burd <greg@burd.me>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Amit Langote <amitlangote09@gmail.com>
Reviewed-by: Haibo Yan <tristan.yim@gmail.com>
Reviewed-by: Alexandra Wang <alexandra.wang.oss@gmail.com>
Discussion: http://postgr.es/m/CA+TgmoZ-Jh1T6QyWoCODMVQdhTUPYkaZjWztzP1En4=ZHoKPzw@mail.gmail.com
It added bogus whitespace at the end of a line in the documentation.
It should not have done that.
The pg_overexplain tests must SET debug_parallel_query = false,
not just RESET debug_parallel_query, or we get failures on test
machines that make debug_parallel_query = true the defualt.
There's a fair amount of information in the Plan and PlanState trees
that isn't printed by any existing EXPLAIN option. This means that,
when working on the planner, it's often necessary to rely on facilities
such as debug_print_plan, which produce excessively voluminous
output. Hence, use the new EXPLAIN extension facilities to implement
EXPLAIN (DEBUG) and EXPLAIN (RANGE_TABLE) as extensions to the core
EXPLAIN facility.
A great deal more could be done here, and the specific choices about
what to print and how are definitely arguable, but this is at least
a starting point for discussion and a jumping-off point for possible
future improvements.
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviweed-by: Andrei Lepikhov <lepihov@gmail.com> (who didn't like it)
Discussion: http://postgr.es/m/CA+TgmoZfvQUBWQ2P8iO30jywhfEAKyNzMZSR+uc2xr9PZBw6eQ@mail.gmail.com
