Fix handling of updated tuples in the MERGE statement

This branch missed the IsolationUsesXactSnapshot() check.  That led to EPQ on
repeatable read and serializable isolation levels.  This commit fixes the
issue and provides a simple isolation check for that.  Backpatch through v15
where MERGE statement was introduced.

Reported-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/CAPpHfdvzZSaNYdj5ac-tYRi6MuuZnYHiUkZ3D-AoY-ny8v%2BS%2Bw%40mail.gmail.com
Author: Tender Wang <tndrwang@gmail.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Backpatch-through: 15

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 0d8a66aa9f01bf374488a65ad67107b44c3a5605..2005674838d6295b21e60ae813f5e92b22beb347 100644 (file)
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -3077,6 +3077,11 @@ lmerge_matched:
                                                           *inputslot;
                                        LockTupleMode lockmode;
 
+                                       if (IsolationUsesXactSnapshot())
+                                               ereport(ERROR,
+                                                               (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+                                                                errmsg("could not serialize access due to concurrent update")));
+
                                        /*
                                         * The target tuple was concurrently updated by some other
                                         * transaction. Run EvalPlanQual() with the new version of

diff --git a/src/test/isolation/expected/merge-update.out b/src/test/isolation/expected/merge-update.out
index f5f7e3ba19b1cbe9b55208671771c7020cbafb3c..5170f6ee019073cf3b48c4326e976ae7aea7a37c 100644 (file)
--- a/src/test/isolation/expected/merge-update.out
+++ b/src/test/isolation/expected/merge-update.out
@@ -355,3 +355,28 @@ step c1: COMMIT;
 step pa_merge2c_dup: <... completed>
 ERROR:  MERGE command cannot affect row a second time
 step a2: ABORT;
+
+starting permutation: merge2a c1 s1beginrr merge1 c2
+step merge2a: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge2a' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+       INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+       UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+
+step c1: COMMIT;
+step s1beginrr: BEGIN ISOLATION LEVEL REPEATABLE READ;
+step merge1: 
+  MERGE INTO target t
+  USING (SELECT 1 as key, 'merge1' as val) s
+  ON s.key = t.key
+  WHEN NOT MATCHED THEN
+       INSERT VALUES (s.key, s.val)
+  WHEN MATCHED THEN
+    UPDATE set key = t.key + 1, val = t.val || ' updated by ' || s.val;
+ <waiting ...>
+step c2: COMMIT;
+step merge1: <... completed>
+ERROR:  could not serialize access due to concurrent update

diff --git a/src/test/isolation/specs/merge-update.spec b/src/test/isolation/specs/merge-update.spec
index 3ccd466449898d1ff8bcd97b5369195269164f72..293cdb46b560c6db590bd1059a1e53f136efcacd 100644 (file)
--- a/src/test/isolation/specs/merge-update.spec
+++ b/src/test/isolation/specs/merge-update.spec
@@ -78,6 +78,7 @@ step "pa_merge3"
 }
 step "c1" { COMMIT; }
 step "a1" { ABORT; }
+step "s1beginrr" { BEGIN ISOLATION LEVEL REPEATABLE READ; }
 
 session "s2"
 setup
@@ -167,3 +168,4 @@ permutation "pa_merge2" "c1" "pa_merge2a" "pa_select2" "c2" # succeeds
 permutation "pa_merge3" "pa_merge2b_when" "c1" "pa_select2" "c2" # WHEN not satisfied by updated tuple
 permutation "pa_merge1" "pa_merge2b_when" "c1" "pa_select2" "c2" # WHEN satisfied by updated tuple
 permutation "pa_merge1" "pa_merge2c_dup" "c1" "a2"
+permutation "merge2a" "c1" "s1beginrr" "merge1" "c2"