lost in system tables

I am trying to find the equivalent of these two
Sybase system columns :

check_on_commit (Y/N) - Indicates whether INSERT and
UPDATE commands should wait until the next COMMIT
command to check if foreign keys are valid. A foreign
key is valid if, for each row in the foreign table,
the values in the columns of the foreign key either
contain the NULL value or match the primary key values
in some row of the primary table.

nulls (Y/N) - Indicates whether the columns in the
foreign key are allowed to contain the NULL value.
Note that this setting is independent of the nulls
setting in the columns contained in the foreign key.

Maybe pg_constaint.condeferrable is appropriate for
check_on_commit? I'll appreciate any help

Thanks in advance,
Emil

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