On Thu, Dec 2, 2021 at 9:35 AM Dilip Kumar <dilipbalaut@xxxxxxxxx> wrote:
> I think there is no such view or anything which tells about which
> backend or transaction has more than 64 sub transaction. But if we
> are ready to modify the code then we can LOG that information in
> GetNewTransactionId(), when first time we are marking it overflown.
> if (nxids < PGPROC_MAX_CACHED_SUBXIDS)
> {
> MyProc->subxids.xids[nxids] = xid;
> pg_write_barrier();
> MyProc->subxidStatus.count = substat->count = nxids + 1;
> }
> else
> {
> MyProc->subxidStatus.overflowed = substat->overflowed = true;
> <-- we can log or put breakpoint here and identify which statement is
> creating oeverflow-->
> }
>
> IMHO, it is good to LOG such information if we are not already logging
> this anywhere.
>
I have prepared a small patch to log this information.
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com
From 83aa6b7afbe50c1b2f4404f68c3f1a08bd16f7e8 Mon Sep 17 00:00:00 2001
From: Dilip Kumar <dilipkumar@localhost.localdomain>
Date: Fri, 3 Dec 2021 14:28:41 +0530
Subject: [PATCH] LOG subxid cache overflow message
---
src/backend/access/transam/varsup.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
index a6e98e7..4877aaa 100644
--- a/src/backend/access/transam/varsup.c
+++ b/src/backend/access/transam/varsup.c
@@ -245,8 +245,13 @@ GetNewTransactionId(bool isSubXact)
pg_write_barrier();
MyProc->subxidStatus.count = substat->count = nxids + 1;
}
- else
+ else if (!substat->overflowed)
+ {
+ ereport(LOG,
+ (errmsg("subxid cache for top transaction %u, overflowed",
+ MyProc->xid)));
MyProc->subxidStatus.overflowed = substat->overflowed = true;
+ }
}
LWLockRelease(XidGenLock);
--
1.8.3.1
