1 files changed, 79 insertions, 0 deletions
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcafb..e98286d768b 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,82 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res, int szgid)
+{
+	Assert(OidIsValid(subid));
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid_res, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_from_gid;
+	TransactionId xid_from_gid;
+	char		gid_tmp[GIDSIZE];
+
+	/* Extract the subid and xid from the given GID */
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
+
+	/*
+	 * Check that the given GID has expected format, and at least the subid
+	 * matches.
+	 */
+	if (ret != 2 || subid != subid_from_gid)
+		return false;
+
+	/*
+	 * Reconstruct a temporary GID based on the subid and xid extracted from
+	 * the given GID and check whether the temporary GID and the given GID
+	 * match.
+	 */
+	TwoPhaseTransactionGid(subid, xid_from_gid, gid_tmp, sizeof(gid_tmp));
+
+	return strcmp(gid, gid_tmp) == 0;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+
+	return found;
+}