Fix COMMIT/ROLLBACK AND CHAIN in the presence of subtransactions.

In older branches, COMMIT/ROLLBACK AND CHAIN failed to propagate
the current transaction's properties to the new transaction if
there was any open subtransaction (unreleased savepoint).
Instead, some previous transaction's properties would be restored.
This is because the "if (s->chain)" check in CommitTransactionCommand
examined the wrong instance of the "chain" flag and falsely
concluded that it didn't need to save transaction properties.

Our regression tests would have noticed this, except they used
identical transaction properties for multiple tests in a row,
so that the faulty behavior was not distinguishable from correct
behavior.

Commit 12d768e70 fixed the problem in v15 and later, but only rather
accidentally, because I removed the "if (s->chain)" test to avoid a
compiler warning, while not realizing that the warning was flagging a
real bug.

In v14 and before, remove the if-test and save transaction properties
unconditionally; just as in the newer branches, that's not expensive
enough to justify thinking harder.

Add the comment and extra regression test to v15 and later to
forestall any future recurrence, but there's no live bug in those
branches.

Patch by me, per bug #18118 from Liu Xiang.  Back-patch to v12 where
the AND CHAIN feature was added.

Discussion: https://postgr.es/m/18118-4b72fcbb903aace6@postgresql.org

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 9e3c6481f4415ac007fec300ae9a1c6fe3ec03e1..2a89141b5e06c5548e99faf7720a3fb7020e84d1 100644 (file)
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -2940,8 +2940,8 @@ CommitTransactionCommand(void)
 {
    TransactionState s = CurrentTransactionState;
 
-   if (s->chain)
-       SaveTransactionCharacteristics();
+   /* Must save in case we need to restore below */
+   SaveTransactionCharacteristics();
 
    switch (s->blockState)
    {

diff --git a/src/test/regress/expected/transactions.out b/src/test/regress/expected/transactions.out
index e2ee88071426840c29b770053d820eb4d8fd3d73..2a5d743c4bd316af4dca38aeecf472c8a83f381f 100644 (file)
--- a/src/test/regress/expected/transactions.out
+++ b/src/test/regress/expected/transactions.out
@@ -814,6 +814,46 @@ SHOW transaction_deferrable;
  on
 (1 row)
 
+COMMIT;
+START TRANSACTION ISOLATION LEVEL READ COMMITTED, READ WRITE, DEFERRABLE;
+SHOW transaction_isolation;
+ transaction_isolation 
+-----------------------
+ read committed
+(1 row)
+
+SHOW transaction_read_only;
+ transaction_read_only 
+-----------------------
+ off
+(1 row)
+
+SHOW transaction_deferrable;
+ transaction_deferrable 
+------------------------
+ on
+(1 row)
+
+SAVEPOINT x;
+COMMIT AND CHAIN;  -- TBLOCK_SUBCOMMIT
+SHOW transaction_isolation;
+ transaction_isolation 
+-----------------------
+ read committed
+(1 row)
+
+SHOW transaction_read_only;
+ transaction_read_only 
+-----------------------
+ off
+(1 row)
+
+SHOW transaction_deferrable;
+ transaction_deferrable 
+------------------------
+ on
+(1 row)
+
 COMMIT;
 -- different mix of options just for fun
 START TRANSACTION ISOLATION LEVEL SERIALIZABLE, READ WRITE, NOT DEFERRABLE;

diff --git a/src/test/regress/sql/transactions.sql b/src/test/regress/sql/transactions.sql
index acb7cc1c8dd356360f2b573324b92d78edcdbb76..50ea1ded9b80f1673998209fa54e46691401bf11 100644 (file)
--- a/src/test/regress/sql/transactions.sql
+++ b/src/test/regress/sql/transactions.sql
@@ -469,6 +469,17 @@ SHOW transaction_read_only;
 SHOW transaction_deferrable;
 COMMIT;
 
+START TRANSACTION ISOLATION LEVEL READ COMMITTED, READ WRITE, DEFERRABLE;
+SHOW transaction_isolation;
+SHOW transaction_read_only;
+SHOW transaction_deferrable;
+SAVEPOINT x;
+COMMIT AND CHAIN;  -- TBLOCK_SUBCOMMIT
+SHOW transaction_isolation;
+SHOW transaction_read_only;
+SHOW transaction_deferrable;
+COMMIT;
+
 -- different mix of options just for fun
 START TRANSACTION ISOLATION LEVEL SERIALIZABLE, READ WRITE, NOT DEFERRABLE;
 SHOW transaction_isolation;