Try this for both FK tables:

create table tmp2(idx2 int4, col2 int4, constraint
tmpcon2 foreign key(col2) references tmp1(idx) INITIALLY DEFERRED);

This will defer constraint checks till transaction commit...
though constraint triggers should use SnapshotDirty instead of
SELECT FOR UPDATE anyway.

Did you consider this, Jan?

Vadim

> When two tables (table2 and table3) have foreign keys
> referring to a common table(table1), I am unable to
> have 2 concurrent transactions - one performing insert
> on table1 and the other on table2, when the records
> being inserted have the same foreign key. 
> 
> If I use JDBC, one of the transactions aborts.
> If I open 2 psql sessions and try the same, one just
> waits and does not show the prompt until the other
> transaction has been committed or aborted.
> 
> For example,
> create table tmp1(idx int4, data int4);
> create table tmp2(idx2 int4, col2 int4, constraint
> tmpcon2 foreign key(col2) references tmp1(idx));
> create table tmp3(idx3 int4, col3 int4, constraint
> tmpcon3 foreign key(col3) references tmp1(idx));
> insert into tmp1 values(1, 1);
> 
> Transaction 1 :
> begin work;
> insert into tmp2 values(2, 1);
> 
> Transaction2 :
> begin work;
> insert into tmp3 values(3,1);
> 
> Since such transactions are common for me, for the
> time-being I have dropped the foreign key constraint.
> Any ideas ?
> 
> Rini
> 
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> 

Mon, 9 Oct 2000 16:11:04 -0700 
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
RE: foreign key introduces unnecessary locking ?
Mikheev, Vadim wrote:
> Try this for both FK tables:
>
> create table tmp2(idx2 int4, col2 int4, constraint
> tmpcon2 foreign key(col2) references tmp1(idx) INITIALLY DEFERRED);
>
> This will defer constraint checks till transaction commit...
> though constraint triggers should use SnapshotDirty instead of
> SELECT FOR UPDATE anyway.
>
> Did you consider this, Jan?
>
> Vadim

    Whenever the checks are done, the transaction inserting a new
    reference to the key must ensure that  this  key  cannot  get
    deleted until it is done and it's newly inserted reference is
    visible  to  others.    Otherwise   a   referential   action,
    preventing referenced key deletion (or other action) wouldn't
    see those and it would be possible to violate the constraint.

    I  don't  see  any  other way doing it than obtaining a lock.
    Using SnapshotDirty would mean, that  one  transaction  could
    DELETE  a  reference,  then  another  transaction removes the
    primary key  (because  using  Dirty  the  DELETE  is  already
    visible),  but  now the first transaction rolls back.  Voila,
    constraint violated.


Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#================================================== JanWieck@Yahoo.com #



Sun, 22 Oct 2000 07:26:12 -0500 (EST)
Jan Wieck <janwieck@yahoo.com>
Re: foreign key introduces unnecessary locking ?
> > though constraint triggers should use SnapshotDirty instead of
> > SELECT FOR UPDATE anyway.
> >
> > Did you consider this, Jan?
>
>     Whenever the checks are done, the transaction inserting a new
>     reference to the key must ensure that  this  key  cannot  get
>     deleted until it is done and it's newly inserted reference is
>     visible  to  others.    Otherwise   a   referential   action,
>     preventing referenced key deletion (or other action) wouldn't
>     see those and it would be possible to violate the constraint.
>
>     I  don't  see  any  other way doing it than obtaining a lock.
>     Using SnapshotDirty would mean, that  one  transaction  could
>     DELETE  a  reference,  then  another  transaction removes the
>     primary key  (because  using  Dirty  the  DELETE  is  already
>     visible),  but  now the first transaction rolls back.  Voila,
>     constraint violated.

Using Dirty transaction removing/updating PK could see that concurrent
xaction attempts to update/insert FK and so would wait for its commit/abort.
Just like now same row writers wait for each other.

Having this, we could insert FK without holding locks over PK. At the moment
of constarint check we would see and wait concurrent PK deletion.

If two xactons will wait for each other then one of them will be aborted.

This behaviour is more natural for MVCC system postulated that
only same-row-writers wait for each other. Why two same FK inserters
should wait for each other if we can avoid this?

Also, is there any way to get deferrable PK/UK constraints? I wonder
why unique index is used for them.

Vadim



Mon, 23 Oct 2000 11:22:28 -0700
"Vadim Mikheev" <vmikheev@sectorbase.com>
Re: foreign key introduces unnecessary locking ?
> Using Dirty transaction removing/updating PK could see that concurrent
> xaction attempts to update/insert FK and so would wait for its
commit/abort.

^^^^^^^^
Of course this will require some function that would take tid as one of
arguments, fetch row and check if someone is updating it.

> Just like now same row writers wait for each other.

Vadim



Mon, 23 Oct 2000 14:29:02 -0700
"Vadim Mikheev" <vmikheev@sectorbase.com>
Re: foreign key introduces unnecessary locking ?