Fix timing issue with ALTER TABLE's validate constraint
An ALTER TABLE to validate a foreign key in which another subcommand
already caused a pending table rewrite could fail due to ALTER TABLE
attempting to validate the foreign key before the actual table rewrite
takes place. This situation could result in an error such as:
ERROR: could not read block 0 in file "base/nnnnn/nnnnn": read only 0 of 8192 bytes
The failure here was due to the SPI call which validates the foreign key
trying to access an index which is yet to be rebuilt.
Similarly, we also incorrectly tried to validate CHECK constraints before
the heap had been rewritten.
The fix for both is to delay constraint validation until phase 3, after
the table has been rewritten. For CHECK constraints this means a slight
behavioral change. Previously ALTER TABLE VALIDATE CONSTRAINT on
inheritance tables would be validated from the bottom up. This was
different from the order of evaluation when a new CHECK constraint was
added. The changes made here aligns the VALIDATE CONSTRAINT evaluation
order for inheritance tables to be the same as ADD CONSTRAINT, which is
generally top-down.
Reported-by: Nazli Ugur Koyluoglu, using SQLancer
Discussion: https://postgr.es/m/CAApHDvp%3DZXv8wiRyk_0rWr00skhGkt8vXDrHJYXRMft3TjkxCA%40mail.gmail.com
Backpatch-through: 9.5 (all supported versions)
Branch
------
REL9_5_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/e20003fa0f8d35fa03bc60273e1cee4558f19e41
Modified Files
--------------
src/backend/commands/tablecmds.c | 159 ++++++++++--------------------
src/test/regress/expected/alter_table.out | 22 ++++-
src/test/regress/sql/alter_table.sql | 22 +++++
3 files changed, 95 insertions(+), 108 deletions(-)
