From: Alexander Lakhin <exclusion@gmail.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18014: Releasing catcache entries makes schema_to_xmlschema() fail when parallel workers are used
Date: Fri, 21 Jul 2023 12:00:01 +0300
Message-ID: <1a2d5aba-df29-ab8d-65ac-6ffd54d1ac62@gmail.com> (raw)
In-Reply-To: <20230720.172924.535889842187000361.horikyota.ntt@gmail.com>
References: <b2dcd258-82f1-dfe3-498e-9f652a0c0c4b@gmail.com>
<20230720.162802.905550494964943231.horikyota.ntt@gmail.com>
<20230720.164459.2183367718473165651.horikyota.ntt@gmail.com>
<20230720.172924.535889842187000361.horikyota.ntt@gmail.com>
Hello Horiguchi-san,
20.07.2023 11:29, Kyotaro Horiguchi wrote:
> At Thu, 20 Jul 2023 16:44:59 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in
>> Stupid. What we should do here would be ensuring the funtion doesn't
>> invoke parallel workers, maybe.
> So, for testing, I didn't see the error with applying the attached patch.
> There are other SPI calls but I didn't see them at all.
>
Thank you for looking into it!
I think that we need to determine the level where the problem that should
be fixed is:
1) test xmlmap fails sporadically due to the catalog changes caused by
parallel tests activity
2) schema_to_xmlschemaX() can fail when parallel workers are used
3) has_table_privilegeX() can fail sporadically when executed within a
parallel worker
4) SearchSysCacheX(RELOID, ...) can switch to a newer catalog snapshot,
when repeated in a parallel worker
The patch proposed fixes the issue on level 2, but that error still can be
seen on level 3. For example, you can replace
SELECT schema_to_xmlschema('testxmlschema_$c', true, false, '');
in the above script with
SELECT oid FROM pg_catalog.pg_class WHERE relnamespace = 1 AND relkind IN ('r', 'm', 'v') AND
pg_catalog.has_table_privilege (oid, 'SELECT');
Probably, similar errors can also occur with
"SELECT * FROM information_schema.tables" or with other
information_schema views, that call has_table_privilege().
But if it's okey to have sporadic errors on lower levels, then may be just
fix the issue on level 1. Please look at the patch attached, that makes
schema_get_xml_visible_tables(Oid nspid) isolated from changes in other
namespaces.
Best regards,
Alexander
Attachments:isolate-schema_get_xml_visible_tables.patch (text/x-patch, 884B) downloaddiff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.cindex 866d0d649a..5b6291c6c9 100644--- a/src/backend/utils/adt/xml.c+++ b/src/backend/utils/adt/xml.c@@ -2723,12 +2723,13 @@ schema_get_xml_visible_tables(Oid nspid)
StringInfoData query;
initStringInfo(&query);
- appendStringInfo(&query, "SELECT oid FROM pg_catalog.pg_class"+ appendStringInfo(&query, "SELECT oid FROM "+ " (SELECT oid, relname FROM pg_catalog.pg_class"
" WHERE relnamespace = %u AND relkind IN ("
CppAsString2(RELKIND_RELATION) ","
CppAsString2(RELKIND_MATVIEW) ","
- CppAsString2(RELKIND_VIEW) ")"- " AND pg_catalog.has_table_privilege (oid, 'SELECT')"+ CppAsString2(RELKIND_VIEW) ") OFFSET 0) c"+ " WHERE pg_catalog.has_table_privilege (oid, 'SELECT')"
" ORDER BY relname;", nspid);
return query_to_oid_list(query.data);
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To: pgsql-bugs@postgresql.org
Cc: exclusion@gmail.com, horikyota.ntt@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18014: Releasing catcache entries makes schema_to_xmlschema() fail when parallel workers are used
In-Reply-To: <1a2d5aba-df29-ab8d-65ac-6ffd54d1ac62@gmail.com>
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