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 1e22c1eefc16a1b666626178261cadbe4073cb43..a5292c358aa3e5e542a0d74e543d12914d3e9c41 100644 (file)
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -405,6 +405,24 @@ 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 057dae056be759ebf2b94caadfae73d47c4e0397..6a3e33e08102877e299aaf6b51025368f8f52790 100644 (file)
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -235,6 +235,19 @@ 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 518703141fa6e95afc632bad1b98622520d56ae4..392757001f9b634d3888301ff20676025a31d2d9 100644 (file)
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -1334,15 +1334,19 @@ 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;
        }
    }