question about relation_open

Hi,

I want to call the function ReadBufferExtended
to get the raw data of a given buffer
and I've read in some examples that I need to call relation_open
first, in order to get a Relation variable and also lock the relation.

The function relation_open returns a non NULL pointer in my extension, but
then the last line in the following snippet crashes postgres.

You mentioned that the postgres crashes. Did you mean it caused a
Segmentation fault or something else like PANIC?
If possible, can you share a core dump in that case?

Also, can you share any errors that you see in logs when postgres crashes?

Thank you,
Rahila Syed

hi Rahila, thank you for your response,
I mean Segmentation fault, this is what I see in psql

SSL SYSCALL error: EOF detected
The connection to the server was lost. Attempting reset: Failed.
!?>

this is the content of
in /var/log/postgresql/postgresql-14-main.log when a segmentation fault
happens

2025-01-14 12:30:12.092 CET [1538] LOG: server process (PID 34594) was
terminated by signal 11: Erreur de segmentation
2025-01-14 12:30:12.092 CET [1538] DETAIL: Failed process was running:
select visualize_buffers(90);
2025-01-14 12:30:12.092 CET [1538] LOG: terminating any other active
server processes
2025-01-14 12:30:12.097 CET [1538] LOG: all server processes terminated;
reinitializing
2025-01-14 12:30:12.115 CET [34608] LOG: database system was interrupted;
last known up at 2025-01-14 10:36:29 CET
2025-01-14 12:30:12.175 CET [34610] postgres@postgres FATAL: the database
system is in recovery mode
2025-01-14 12:30:12.279 CET [34608] LOG: database system was not properly
shut down; automatic recovery in progress
2025-01-14 12:30:12.281 CET [34608] LOG: redo starts at 0/1CCF820
2025-01-14 12:30:12.281 CET [34608] LOG: invalid record length at
0/1CCF858: wanted 24, got 0
2025-01-14 12:30:12.281 CET [34608] LOG: redo done at 0/1CCF820 system
usage: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
2025-01-14 12:30:12.379 CET [1538] LOG: database system is ready to accept
connections

I don't know how to collect a core dump of postgres, I tried with gdb, but
It doesn't seem to log anything interesting

Le mar. 14 janv. 2025 à 12:27, Rahila Syed <rahilasyed90@gmail.com> a
écrit :

Giampaolo Capelli <giampow@gmail.com> writes:

The function relation_open returns a non NULL pointer in my extension, but
then the last line in the following snippet crashes postgres.

Relation rel;
rel = relation_open(relid, AccessShareLock);

Assert(rel != NULL);
Assert(rel->rd_rel != NULL);
Assert(rel->rd_id != NULL);
elog(INFO, "rel->rd_id not null");
Oid rd_id = rel->rd_id;

Hmm, I'm a little bit doubting your statement that relation_open
succeeded. I wonder if maybe you built your extension without asserts
enabled ...

regards, tom lane

It seems the issue was related to some misconfiguration of my postgresql
server,
I've migrated from pg 14 to 17 and now the issue has disappeared.

Also, I replaced relation_open with table_open

Le mar. 14 janv. 2025 à 15:40, Tom Lane <tgl@sss.pgh.pa.us> a écrit :

Giampaolo Capelli <giampow@gmail.com> writes:

The function relation_open returns a non NULL pointer in my extension,

but

then the last line in the following snippet crashes postgres.

Relation rel;
rel = relation_open(relid, AccessShareLock);

Assert(rel != NULL);
Assert(rel->rd_rel != NULL);
Assert(rel->rd_id != NULL);
elog(INFO, "rel->rd_id not null");
Oid rd_id = rel->rd_id;

Hmm, I'm a little bit doubting your statement that relation_open
succeeded. I wonder if maybe you built your extension without asserts
enabled ...

regards, tom lane

--
Giampaolo Capelli