On Friday, November 24, 2023 7:47 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Thu, Nov 23, 2023 at 2:33 PM Amit Kapila <amit.kapil...@gmail.com> > wrote: > > > > On Thu, Nov 23, 2023 at 1:10 PM Nikhil Benesch <nikhil.bene...@gmail.com> > wrote: > > > > > > While working on Materialize's streaming logical replication from > > > Postgres [0], my colleagues Sean Loiselle and Petros Angelatos > > > (CC'd) discovered today what appears to be a correctness bug in pgoutput, > introduced in v15. > > > > > > The problem goes like this. A table with REPLICA IDENTITY FULL and > > > some data in it... > > > > > > CREATE TABLE t (a int); > > > ALTER TABLE t REPLICA IDENTITY FULL; > > > INSERT INTO t VALUES (1), (2), (3), ...; > > > > > > ...undergoes a schema change to add a new column with a default: > > > > > > ALTER TABLE t ADD COLUMN b bool DEFAULT false NOT NULL; > > > > > > PostgreSQL is smart and does not rewrite the entire table during the > > > schema change. Instead it updates the tuple description to indicate > > > to future readers of the table that if `b` is missing, it should be > > > filled in with the default value, `false`. > > > > > > Unfortunately, since v15, pgoutput mishandles missing attributes. If > > > a downstream server is subscribed to changes from t via the pgoutput > > > plugin, when a row with a missing attribute is updated, e.g.: > > > > > > UPDATE t SET a = 2 WHERE a = 1 > > > > > > pgoutput willz incorrectly report b's value as NULL in the old tuple, > > > rather than false. > > > > > > > Thanks, I could reproduce this behavior. I'll look into your patch. > > > > I verified your fix is good and made minor modifications in the comment. Note, > that the test doesn't work for PG15, needs minor modifications.
Thank you for fixing and reviewing the fix! The fix also looks good to me. I verified that it can fix the problem in HEAD ~ PG15 and the added tap test can detect the problem without the fix. I tried to rebase the patch on PG15, and combines some queries into one safe_sql block to simplify the code. Here are the patches for all branches. Best Regards, Hou zj
v3-HEAD-PG16-0001-Avoid-unconditionally-filling-in-missing-values-w.patch
Description: v3-HEAD-PG16-0001-Avoid-unconditionally-filling-in-missing-values-w.patch
v3-PG15-0001-Avoid-unconditionally-filling-in-missing-values-w.patch
Description: v3-PG15-0001-Avoid-unconditionally-filling-in-missing-values-w.patch
