On 9/19/18 4:53 AM, Michael Paquier wrote: > On Tue, Sep 18, 2018 at 12:32:54PM +0200, Adrien NAYRAT wrote: >> A few days ago I was surprised a CREATE TABLE containing FK constraint was >> stuck due to an automatic vacuum freeze (which took ShareUpdateExclusiveLock >> if I remember) on referenced table. > > Right. See the top of vacuum_rel() where lmode is set. > >> After digging into the code I found theses lines in tablecmds.c : >> >> /* >> * Grab ShareRowExclusiveLock on the pk table, so that someone doesn't >> * delete rows out from under us. >> */ >> >> Maybe it should be documented in theses pages? >> >> https://www.postgresql.org/docs/current/static/sql-createtable.html >> https://www.postgresql.org/docs/current/static/sql-altertable.html >> >> If you agree I can send a patch. > > That looks like a good idea. Are you thinking about adding a comment > about that in "ADD table_constraint" for the ALTER TABLE page, and in > "FOREIGN KEY" for the CREATE TABLE page?
Yes, here is the patch Thanks -- Adrien
diff --combined doc/src/sgml/ref/alter_table.sgml
index 1e4a327327,ec6b4c3311..0000000000
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@@ -377,11 -377,6 +377,11 @@@ WITH ( MODULUS <replaceable class="para
are added to partitioned tables; see <xref linkend="sql-createtable" />.
</para>
+ <para>
+ Adding a foreign key requires taking a <literal>SHARE ROW EXCLUSIVE<literal>
+ lock on the referenced table.
+ </para>
+
</listitem>
</varlistentry>
diff --combined doc/src/sgml/ref/create_table.sgml
index a974bea6b1,5a19f94ce9..0000000000
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@@ -993,8 -993,6 +993,8 @@@ WITH ( MODULUS <replaceable class="para
unique or primary key constraint in the referenced table. The user
must have <literal>REFERENCES</literal> permission on the referenced table
(either the whole table, or the specific referenced columns).
+ Addding a foreign key constraint requires taking a <literal>SHARE ROW
+ EXCLUSIVE <literal> lock on the referenced table.
Note that foreign key constraints cannot be defined between temporary
tables and permanent tables. Also note that while it is possible to
define a foreign key on a partitioned table, it is not possible to
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