Hi,
I found that the consume_xids function incorrectly advances XIDs as
shown:
postgres=# select txid_current();
txid_current
--------------
746
(1 row)
postgres=# select consume_xids('100');
consume_xids
--------------
847
(1 row)
In the example, the consume_xids function consumes 100 XIDs when XID =
746, so the desired outcome from consume_xids should be 746 + 100 = 846,
which differs from the actual outcome, 847.
Behavior inside a transaction block:
postgres=# select txid_current();
txid_current
--------------
1410
(1 row)
postgres=# begin;
BEGIN
postgres=*# select consume_xids('100');
consume_xids
--------------
1511
(1 row)
postgres=*# select consume_xids('100');
consume_xids
--------------
1521
(1 row)
Here, the first call inside the transaction block consumes 100+1 XIDs
(incorrect), while the second call consumes exactly 100 XIDs (as
expected)
Summary:
The function performs incorrectly when:
- Outside of a transaction block
- The first call inside a transaction block
But works correctly when:
- After the second call inside a transaction block
The issue arises because consume_xids does not correctly count the
consumed XIDs when it calls the GetTopTransactionId function, which
allocates a new XID when none has been assigned.
With the attached patch, the consume_xids works as expected, both inside
and outside of transaction blocks as shown below:
postgres=# select txid_current();
txid_current
--------------
1546
(1 row)
postgres=# select consume_xids('100');
consume_xids
--------------
1646
(1 row)
postgres=# begin;
BEGIN
postgres=*# select consume_xids('100');
consume_xids
--------------
1746
(1 row)
postgres=*# select consume_xids('100');
consume_xids
--------------
1846
(1 row)
Regards,
YushiFrom 59bc3f300b8447a407c8f90ebb542d1c0ef0e932 Mon Sep 17 00:00:00 2001
From: Yushi Ogiwara <yushiogiw...@keio.jp>
Date: Fri, 11 Oct 2024 14:45:26 +0900
Subject: [PATCH] fix xid
---
src/test/modules/xid_wraparound/xid_wraparound.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/src/test/modules/xid_wraparound/xid_wraparound.c b/src/test/modules/xid_wraparound/xid_wraparound.c
index dce81c0c6d..c5f3b717cf 100644
--- a/src/test/modules/xid_wraparound/xid_wraparound.c
+++ b/src/test/modules/xid_wraparound/xid_wraparound.c
@@ -89,7 +89,11 @@ consume_xids_common(FullTransactionId untilxid, uint64 nxids)
* the cache overflows, but beyond that, we don't keep track of the
* consumed XIDs.
*/
- (void) GetTopTransactionId();
+ if(!FullTransactionIdIsValid(GetTopFullTransactionIdIfAny()))
+ {
+ (void) GetTopTransactionId();
+ consumed++;
+ }
for (;;)
{
--
2.40.1
