[ redirecting to pgsql-hackers as the more relevant list ]
I wrote:
> PegoraroF10 <[email protected]> writes:
>> I tried sometime ago ... but with no responses, I ask you again.
>> pg_publication_tables is a view that is used to refresh publication, but as
>> we have 15.000 tables, it takes hours and doesn't complete. If I change that
>> view I can have an immediate result. The question is: Can I change that view
>> ? There is some trouble changing those system views ?
> Hmm ... given that pg_get_publication_tables() shouldn't return any
> duplicate OIDs, it does seem unnecessarily inefficient to put it in
> an IN-subselect condition. Peter, is there a reason why this isn't
> a straight lateral join? I get a much saner-looking plan from
> FROM pg_publication P, pg_class C
> - JOIN pg_namespace N ON (N.oid = C.relnamespace)
> - WHERE C.oid IN (SELECT relid FROM pg_get_publication_tables(P.pubname));
> + JOIN pg_namespace N ON (N.oid = C.relnamespace),
> + LATERAL pg_get_publication_tables(P.pubname)
> + WHERE C.oid = pg_get_publication_tables.relid;
For the record, the attached seems like what to do here. It's easy
to show that there's a big performance gain even for normal numbers
of tables, eg if you do
CREATE PUBLICATION mypub FOR ALL TABLES;
SELECT * FROM pg_publication_tables;
in the regression database, the time for the select drops from ~360ms
to ~6ms on my machine. The existing view's performance will drop as
O(N^2) the more publishable tables you have ...
Given that this change impacts the regression test results, project
rules say that it should come with a catversion bump. Since we are
certainly going to have a catversion bump before beta2 because of
the pg_statistic_ext permissions business, that doesn't seem like
a reason not to push it into v12 --- any objections?
regards, tom lane
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 566100d..52a6c31 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -258,9 +258,10 @@ CREATE VIEW pg_publication_tables AS
P.pubname AS pubname,
N.nspname AS schemaname,
C.relname AS tablename
- FROM pg_publication P, pg_class C
- JOIN pg_namespace N ON (N.oid = C.relnamespace)
- WHERE C.oid IN (SELECT relid FROM pg_get_publication_tables(P.pubname));
+ FROM pg_publication P,
+ LATERAL pg_get_publication_tables(P.pubname) GPT,
+ pg_class C JOIN pg_namespace N ON (N.oid = C.relnamespace)
+ WHERE C.oid = GPT.relid;
CREATE VIEW pg_locks AS
SELECT * FROM pg_lock_status() AS L;
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 0c392e5..4363ca1 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1441,10 +1441,10 @@ pg_publication_tables| SELECT p.pubname,
n.nspname AS schemaname,
c.relname AS tablename
FROM pg_publication p,
+ LATERAL pg_get_publication_tables((p.pubname)::text) gpt(relid),
(pg_class c
JOIN pg_namespace n ON ((n.oid = c.relnamespace)))
- WHERE (c.oid IN ( SELECT pg_get_publication_tables.relid
- FROM pg_get_publication_tables((p.pubname)::text) pg_get_publication_tables(relid)));
+ WHERE (c.oid = gpt.relid);
pg_replication_origin_status| SELECT pg_show_replication_origin_status.local_id,
pg_show_replication_origin_status.external_id,
pg_show_replication_origin_status.remote_lsn,
