[YSQL] Failed txn restarts with UPDATE ... RETURNING queries

[pao214]

Jira Link: DB-10929

Description

Issue

Consider the following diff

diff --git a/java/yb-pgsql/src/test/java/org/yb/pgsql/TestPgTransparentRestarts.java b/java/yb-pgsql/src/test/java/org/yb/pgsql/TestPgTransparentRestarts.java
index 43ab3c8f5a..f1b5211126 100644
--- a/java/yb-pgsql/src/test/java/org/yb/pgsql/TestPgTransparentRestarts.java
+++ b/java/yb-pgsql/src/test/java/org/yb/pgsql/TestPgTransparentRestarts.java
@@ -510,6 +510,19 @@ public class TestPgTransparentRestarts extends BasePgSQLTest {
     }
   }
 
+  /*
+   * Long strings shouldn't leak read restarts even when retuning.
+   */
+  @Test
+  public void testUpdateLong() throws Exception {
+    new RegularDmlStatementTester(
+        getConnectionBuilder(),
+        "UPDATE test_rr set i=1 RETURNING *",
+        getLongString(),
+        false /* is_deadlock_possible */
+    ).runTest();
+  }
+
   //
   // Helpers methods
   //

This is an update returning operation that has txn restarts because of txn conflicts with concurrent inserts.

Here is the log

ts1|pid96746|:29457|http://127.0.0.32:21406 	Query: UPDATE test_rr set i=1 RETURNING *
ts1|pid96746|:29457|http://127.0.0.32:21406 	Error: Restart read required at: { read: { days: 19829 time: 20:04:00.296831 } local_limit: { days: 19829 time: 20:04:00.296831 } global_limit: <min> in_txn_limit: <max> serial_no: 0 }
ts1|pid96746|:29457|http://127.0.0.32:21406 	Attempt No: 0
ts1|pid96746|:29457|http://127.0.0.32:21406 2024-04-16 20:04:00.302 PDT [96851] STATEMENT:  UPDATE test_rr set i=1 RETURNING *
ts1|pid96746|:29457|http://127.0.0.32:21406 TRAP: FailedAssertion("!(portal->holdContext == ((void*)0))", File: "../../../../../../../src/postgres/src/backend/utils/mmgr/portalmem.c", Line: 343)
ts1|pid96746|:29457|http://127.0.0.32:21406 2024-04-16 20:04:00.316 PDT [96852] LOG:  Restart is possible

Root Cause

When restarting a txn, we also restart the portal.

Below is an excerpt from yb_restart_portal

	/* delete tuplestore storage, if any */
	if (portal->holdContext)
		MemoryContextDelete(portal->holdContext);

portal->holdContext is not assigned to NULL, making it a dangling reference.

Simply assign it to NULL.

Impact

Affects debug builds.

Issue Type

kind/bug

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