From 4526951d564a7eed512b4a0ac3b5893e0a115690 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 2 Dec 2019 16:31:03 -0500 Subject: Make postgres_fdw's "Relations" output agree with the rest of EXPLAIN. The relation aliases shown in the "Relations" line for a foreign scan didn't always agree with those used in the rest of EXPLAIN's output. The regression test result changes appearing here provide examples. It's really impossible for postgres_fdw to duplicate EXPLAIN's alias assignment logic during postgresGetForeignRelSize(), because of the de-duplication that EXPLAIN does on a global basis --- and anyway, trying to duplicate that would be unmaintainable. Instead, just put numeric rangetable indexes into the string, and convert those to table names/aliases in postgresExplainForeignScan, which does have access to the results of ruleutils.c's alias assignment logic. Aside from being more reliable, this shifts some work from planning to EXPLAIN, which is a good tradeoff for performance. (I also changed from using StringInfo to using psprintf, which makes the code slightly simpler and reduces its memory consumption.) A kluge required by this solution is that we have to reverse-engineer the rtoffset applied by setrefs.c. If that logic ever fails (presumably because the member tables of a join got offset by different amounts), we'll need some more cooperation with setrefs.c to keep things straight. But for now, there's no need for that. Arguably this is a back-patchable bug fix, but since this is a mostly cosmetic issue and there have been no field complaints, I'll refrain for now. Discussion: https://postgr.es/m/12424.1575168015@sss.pgh.pa.us --- contrib/postgres_fdw/postgres_fdw.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'contrib/postgres_fdw/postgres_fdw.h') diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h index bdefe0c40e2..ea052872c3e 100644 --- a/contrib/postgres_fdw/postgres_fdw.h +++ b/contrib/postgres_fdw/postgres_fdw.h @@ -87,11 +87,14 @@ typedef struct PgFdwRelationInfo int fetch_size; /* fetch size for this remote table */ /* - * Name of the relation while EXPLAINing ForeignScan. It is used for join - * relations but is set for all relations. For join relation, the name - * indicates which foreign tables are being joined and the join type used. + * Name of the relation, for use while EXPLAINing ForeignScan. It is used + * for join and upper relations but is set for all relations. For a base + * relation, this is really just the RT index as a string; we convert that + * while producing EXPLAIN output. For join and upper relations, the name + * indicates which base foreign tables are included and the join type or + * aggregation type used. */ - StringInfo relation_name; + char *relation_name; /* Join information */ RelOptInfo *outerrel; -- cgit v1.2.3