[PATCH] Fix memory leak of primary_sysid in walreceiver
Hi, Hackers,
In WalReceiverMain(), the outer streaming loop calls
walrcv_identify_system() once per iteration to verify the primary's
system identifier:
primary_sysid = walrcv_identify_system(wrconn, &primaryTLI);
...
if (strcmp(primary_sysid, standby_sysid) != 0)
ereport(ERROR, ...);
walrcv_identify_system() (libpqrcv_identify_system() in
libpqwalreceiver.c) returns a pstrdup()'d string, but the caller
never frees it. Each streaming restart therefore leaks the string.
The error path is unaffected because the surrounding memory context
is reset on ERROR.
The attached patch adds a pfree(primary_sysid) right after the
comparison.
This dates back to commit 78c8c814390 ("Refactor libpqwalreceiver",
2016), so it should be a back-patch candidate as well.
No new tests are added; the fix only releases resources and does not
change observable behavior. `make check` and the streaming replication
TAP test (src/test/recovery/t/001_stream_rep.pl) pass with the patch
applied.
Patch attached.
Regards,
DaeMyung Kang
Attachments:
0002-Fix-memory-leak-of-primary_sysid-in-walreceiver.patchtext/x-patch; name=0002-Fix-memory-leak-of-primary_sysid-in-walreceiver.patchDownload+1-0
On Mon, Apr 27, 2026 at 02:01:30AM +0900, DaeMyung Kang wrote:
The attached patch adds a pfree(primary_sysid) right after the
comparison.
My first impression was that it does not matter because I was under
the impression that this code path is only reached once, but that's
not the case: a WAL receiver could stay around waiting for
instructions before retrying a connection.
I doubt that this is worth bothering for in the back branches, as it
just means a small leak each time we switch to a new TLI repeatedly,
something that would matter mostly for a cascading standby where we
don't want to change the connection point (a SIGHUP'd primary_conninto
enforces a WAL receiver shutdown). Let's clean up on HEAD, though.
--
Michael