Re: SQL Property Graph Queries (SQL/PGQ)

Hi Ashutosh, Junwang,

On Tue, Mar 11, 2025 at 4:22 PM Ashutosh Bapat
<ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> wrote:
> On Wed, Feb 26, 2025 at 8:04 PM Junwang Zhao <zhjwpku(at)gmail(dot)com> wrote:
> > I added a trivial fix(v12-0014) that called table_open/table_close in
> > rewriteGraphTable, it now passed the regression test and cirrus ci test,
> > but I'm not sure it's the correct fix.
> >
> > I hope Ashutosh can chime in and take a look at this problem.
>
> 2. Following Assertion is failing, the assertion was added recently.
> TRAP: failed Assert("IsParallelWorker() ||
> CheckRelationOidLockedByMe(rte->relid, AccessShareLock, true)"), File:
> "../../coderoot/pg/src/backend/executor/execMain.c", Line: 695, PID:
> 303994
> postgres: ashutosh regression [local]
> SELECT(ExceptionalCondition+0xbe)[0x5c838c5d7114]
> postgres: ashutosh regression [local]
> SELECT(ExecCheckPermissions+0xf8)[0x5c838c11fb9c]
> postgres: ashutosh regression [local] SELECT(+0x38223f)[0x5c838c12023f]
> postgres: ashutosh regression [local]
> SELECT(standard_ExecutorStart+0x2f8)[0x5c838c11f223]
> postgres: ashutosh regression [local] SELECT(ExecutorStart+0x69)[0x5c838c11ef22]
> postgres: ashutosh regression [local] SELECT(PortalStart+0x368)[0x5c838c3d991a]
> postgres: ashutosh regression [local] SELECT(+0x63458e)[0x5c838c3d258e]
> postgres: ashutosh regression [local] SELECT(PostgresMain+0x9eb)[0x5c838c3d7cf0]
> postgres: ashutosh regression [local] SELECT(+0x630178)[0x5c838c3ce178]
> postgres: ashutosh regression [local]
> SELECT(postmaster_child_launch+0x137)[0x5c838c2da677]
> postgres: ashutosh regression [local] SELECT(+0x5431b4)[0x5c838c2e11b4]
> postgres: ashutosh regression [local] SELECT(+0x54076a)[0x5c838c2de76a]
> postgres: ashutosh regression [local]
> SELECT(PostmasterMain+0x15f8)[0x5c838c2de04d]
> postgres: ashutosh regression [local] SELECT(main+0x3a1)[0x5c838c1b12be]
> /lib/x86_64-linux-gnu/libc.so.6(+0x29d90)[0x7eda9ea29d90]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80)[0x7eda9ea29e40]
> postgres: ashutosh regression [local] SELECT(_start+0x25)[0x5c838be7c025]
> 2025-03-11 11:40:01.696 IST postmaster[303081] LOG: client backend
> (PID 303994) was terminated by signal 6: Aborted
> 2025-03-11 11:40:01.696 IST postmaster[303081] DETAIL: Failed process
> was running: select * from atpgv1;
> I tried to investigate the Assertion, it's failing for property graph
> RTE which is turned into subquery RTE. It has the right lock mode set,
> but I haven't been able to figure out where the lock is supposed to be
> taken or where it's released. If we just prepare the failing query and
> execute the prepared statement, it does not trip the assertion. Will
> investigate it more.

I reproduced the crash using the example Junwang gave.

The problem seems to be that RTEs of rtekind RTE_GRAPH_TABLE are not
handled in AcquireRewriteLocks(). You'll need to add a case for
RTE_GRAPH_TABLE similar to RTE_RELATION in the following switch of
that function:

/*
* First, process RTEs of the current query level.
*/
rt_index = 0;
foreach(l, parsetree->rtable)
{
RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
Relation rel;
LOCKMODE lockmode;
List *newaliasvars;
Index curinputvarno;
RangeTblEntry *curinputrte;
ListCell *ll;

++rt_index;
switch (rte->rtekind)
{
case RTE_RELATION:

which could be as simple as the following (fixes the crash!) or
something that's specific to RTE_GRAPH_TABLE:

diff --git a/src/backend/rewrite/rewriteHandler.c
b/src/backend/rewrite/rewriteHandler.c
index c51dd3d2ee4..8fa6edb90eb 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -174,6 +174,7 @@ AcquireRewriteLocks(Query *parsetree,
switch (rte->rtekind)
{
case RTE_RELATION:
+ case RTE_GRAPH_TABLE:

--
Thanks, Amit Langote