Relax overly strict assertion

Ever since its birth, ReorderBufferBuildTupleCidHash() has contained an
assertion that a catalog tuple cannot change Cmax after acquiring one.  But
that's wrong: if a subtransaction executes DDL that affects that catalog
tuple, and later aborts and another DDL affects the same tuple, it will
change Cmax.  Relax the assertion to merely verify that the Cmax remains
valid and monotonically increasing, instead.

Add a test that tickles the relevant code.

Diagnosed by, and initial patch submitted by: Arseny Sher
Co-authored-by: Arseny Sher
Discussion: https://postgr.es/m/874l9p8hyw.fsf@ars-thinkpad

diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index cb44941ede00743973c72b716994b23451bf0a10..3e6aa93187a87c78a5c91f53910e06dd4d3f8bbb 100644 (file)
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -398,6 +398,24 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
  COMMIT
 (6 rows)
 
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+                       data                       
+--------------------------------------------------
+ BEGIN
+ table public.tr_sub_ddl: INSERT: data[bigint]:43
+ COMMIT
+(3 rows)
+
 /*
  * Check whether treating a table as a catalog table works somewhat
  */

diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index 228fe33685b4f5ad6b797b12ba7b2460868fe3bf..e6e055266c598a76d44c660e0e83b0a3202e6677 100644 (file)
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -234,6 +234,19 @@ INSERT INTO tr_sub(path) VALUES ('5-top-1-#1');
 COMMIT;
 
 
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
+-- check that DDL in aborted subtransactions handled correctly
+CREATE TABLE tr_sub_ddl(data int);
+BEGIN;
+SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE text;
+INSERT INTO tr_sub_ddl VALUES ('blah-blah');
+ROLLBACK TO SAVEPOINT a;
+ALTER TABLE tr_sub_ddl ALTER COLUMN data TYPE bigint;
+INSERT INTO tr_sub_ddl VALUES(43);
+COMMIT;
+
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 

diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 9298b710c44d8a6608d55028426e1c8a6eac21d9..dc4e37b9c32eb858f758b3e84f187db53e004299 100644 (file)
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -1327,15 +1327,19 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
                }
                else
                {
+                       /*
+                        * Maybe we already saw this tuple before in this transaction,
+                        * but if so it must have the same cmin.
+                        */
                        Assert(ent->cmin == change->data.tuplecid.cmin);
-                       Assert(ent->cmax == InvalidCommandId ||
-                                  ent->cmax == change->data.tuplecid.cmax);
 
                        /*
-                        * if the tuple got valid in this transaction and now got deleted
-                        * we already have a valid cmin stored. The cmax will be
-                        * InvalidCommandId though.
+                        * cmax may be initially invalid, but once set it can only grow,
+                        * and never become invalid again.
                         */
+                       Assert((ent->cmax == InvalidCommandId) ||
+                                  ((change->data.tuplecid.cmax != InvalidCommandId) &&
+                                       (change->data.tuplecid.cmax > ent->cmax)));
                        ent->cmax = change->data.tuplecid.cmax;
                }
        }