gfphoenix78 commented on PR #1890:
URL: https://github.com/apache/cloudberry/pull/1890#issuecomment-5288714509
The problem is:
```
gpadmin=# create temp table ttmp(a int);
ERROR: global xmin (1076) is higher than transaction xmin (1075)
(procarray.c:3298) (seg0 127.0.0.1:7002 pid=2466718) (procarray.c:3298)
LINE 1: create temp table ttmp(a int);
^
```
repro:
```sql
-- prepare
drop table if exists t1;
create table t1(a int);
-- T1
1: begin;
1: insert into t1 select i from generate_series(1,10)i;
-- to see the local xid on segments
1: select gp_segment_id, xmin, * from t1;
-- T2, will trigger the error
2: set optimizer=off; -- invoke the QE backend on segments
-- gdb attach to one of the QEs and break after release the ProcArrayLock
-- gdb -p xxxx
-- > b procarray.c:3303
-- > c
-- the following sql will be break when running GetSnapshotData
2: create temp table ttmp(a int);
-- rollback T1
1: rollback;
-- running SQL that advance DistributedLogShared.oldestXmin
1: insert into t1 select i from generate_series(1,10)i;
-- gdb: the QE of T2 should be still hanged in GetSnapshotData
-- quit the gdb now
-- > quit
-- now, the above SQL to create temp table will fail
```
gdb break the function GetSnapshotData at:
```c
/*
* GP: In computing Globals, also take distributed snapshots into
* account.
*/
if (TransactionIdPrecedes(xmin, globalxmin))
globalxmin = xmin;
if (!IS_QUERY_DISPATCHER())
```
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