MIME-Version: 1.0
From: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Date: Wed, 8 Apr 2026 19:03:31 -0700
Message-ID: 
 <CAHg+QDcN-n3NUqgRtj=BQb9fFQmH8-DeEROCr=PDbw_BBRKOYA@mail.gmail.com>
Subject: Bug: WAIT FOR LSN crashes with assertion failure inside PL/pgSQL DO
 blocks and procedures
To: Alexander Korotkov <aekorotkov@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Content-Type: multipart/mixed; boundary="000000000000cf2e70064efd6d31"
Archived-At: 
 <https://www.postgresql.org/message-id/CAHg%2BQDcN-n3NUqgRtj%3DBQb9fFQmH8-DeEROCr%3DPDbw_BBRKOYA%40mail.gmail.com>
Precedence: bulk

--000000000000cf2e70064efd6d31
Content-Type: multipart/alternative; boundary="000000000000cf2e6f064efd6d2f"

--000000000000cf2e6f064efd6d2f
Content-Type: text/plain; charset="UTF-8"

Hi hackers, Alexander,

An assertion failure (server crash in assert-enabled builds) occurs when
WAIT FOR LSN ... INTO is used inside PL/pgSQL DO blocks or within void
procedures.

Repro:

-- Run this on a standby

CREATE PROCEDURE test_wait()
  LANGUAGE plpgsql AS $$
  DECLARE
    result text;
  BEGIN
    WAIT FOR LSN '0/1234' INTO result;
    RAISE NOTICE '%', result;
  END;
  $$;
  CALL test_wait();


The WAIT FOR itself succeeds, but the very next PL/pgSQL statement that
requires a snapshot crashes the backend with:

  TRAP: failed Assert("portal->portalSnapshot == NULL"),
  File: "pquery.c", Line: 1776

Attached patches for both the test case and a potential fix. Please review.

Thanks,
Satya

--000000000000cf2e6f064efd6d2f
Content-Type: text/html; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Hi hackers, Alexander,<div><br></div><div>An assertion fai=
lure (server crash in assert-enabled builds) occurs when WAIT FOR LSN ... I=
NTO is used inside PL/pgSQL DO blocks or within void procedures.</div><div>=
<br></div><div>Repro:</div><div><br></div><div>-- Run this on a standby</di=
v><div><br></div><div>CREATE PROCEDURE test_wait()<br>=C2=A0 LANGUAGE plpgs=
ql AS $$<br>=C2=A0 DECLARE<br>=C2=A0 =C2=A0 result text;<br>=C2=A0 BEGIN<br=
>=C2=A0 =C2=A0 WAIT FOR LSN &#39;0/1234&#39; INTO result;<br>=C2=A0 =C2=A0 =
RAISE NOTICE &#39;%&#39;, result;<br>=C2=A0 END;<br>=C2=A0 $$;<br>=C2=A0 CA=
LL test_wait();</div><div><br></div><div><br></div><div>The WAIT FOR itself=
 succeeds, but the very next PL/pgSQL statement that requires a snapshot cr=
ashes the backend with:<br><br>=C2=A0 TRAP: failed Assert(&quot;portal-&gt;=
portalSnapshot =3D=3D NULL&quot;),<br>=C2=A0 File: &quot;pquery.c&quot;, Li=
ne: 1776<br><br></div><div>Attached patches for both the test case and a po=
tential fix. Please review.</div><div><br></div><div>Thanks,</div><div>Saty=
a</div><div><br></div></div>

--000000000000cf2e6f064efd6d2f--

--000000000000cf2e70064efd6d31
Content-Type: application/octet-stream;
	name="0002-Add-regression-tests-for-WAIT-FOR-LSN-inside-PL-pgSQ.patch"
Content-Disposition: attachment;
	filename="0002-Add-regression-tests-for-WAIT-FOR-LSN-inside-PL-pgSQ.patch"
Content-Transfer-Encoding: base64
Content-ID: <f_mnqtze761>
X-Attachment-Id: f_mnqtze761
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--000000000000cf2e70064efd6d31
Content-Type: application/octet-stream;
	name="0001-Fix-assertion-failure-in-WAIT-FOR-LSN-when-used-insi.patch"
Content-Disposition: attachment;
	filename="0001-Fix-assertion-failure-in-WAIT-FOR-LSN-when-used-insi.patch"
Content-Transfer-Encoding: base64
Content-ID: <f_mnqtze6z0>
X-Attachment-Id: f_mnqtze6z0

RnJvbSAxNmFjZTYwZjgyMDYyZjBmMTNmYzE4MTQwODViMDQ1YWVkZDZmMjAyIE1vbiBTZXAgMTcg
MDA6MDA6MDAgMjAwMQpGcm9tOiBTYXR5YSBOYXJsYXB1cmFtIDxzYXR5YW5hcmxhcHVyYW1AZ21h
aWwuY29tPgpEYXRlOiBUaHUsIDkgQXByIDIwMjYgMDA6NTA6MjAgKzAwMDAKU3ViamVjdDogW1BB
VENIIHYxIDEvMl0gRml4IGFzc2VydGlvbiBmYWlsdXJlIGluIFdBSVQgRk9SIExTTiB3aGVuIHVz
ZWQgaW5zaWRlCiBQTC9wZ1NRTAoKV0FJVCBGT1IgTFNOIC4uLiBJTlRPIGluc2lkZSBhIERPIGJs
b2NrIGNyYXNoZWQgd2l0aCBhbiBhc3NlcnRpb24gZmFpbHVyZSBpbiAKRW5zdXJlUG9ydGFsU25h
cHNob3RFeGlzdHMoKToKCiAgVFJBUDogZmFpbGVkIEFzc2VydCgicG9ydGFsLT5wb3J0YWxTbmFw
c2hvdCA9PSBOVUxMIiksCiAgRmlsZTogInBxdWVyeS5jIiwgTGluZTogMTc3NgoKVGhlIHJvb3Qg
Y2F1c2Ugd2FzIHRoYXQgRXhlY1dhaXRTdG10KCkgY2FsbGVkIFBvcEFjdGl2ZVNuYXBzaG90KCkg
dG8KcmVsZWFzZSB0aGUgc25hcHNob3QgYmVmb3JlIHdhaXRpbmcsIGJ1dCBkaWQgbm90IGNsZWFy
IHRoZSBhY3RpdmUKcG9ydGFsJ3MgcG9ydGFsU25hcHNob3QgcG9pbnRlci4gIFdoZW4gdGhlIG5l
eHQgUEwvcGdTUUwgc3RhdGVtZW50CnJlcXVpcmluZyBhIHNuYXBzaG90IGNhbGxlZCBFbnN1cmVQ
b3J0YWxTbmFwc2hvdEV4aXN0cygpLCBpdCBmb3VuZAphIHN0YWxlIG5vbi1OVUxMIHBvcnRhbFNu
YXBzaG90IGFuZCBoaXQgdGhlIGFzc2VydGlvbi4KClBvcnRhbFJ1blV0aWxpdHkoKSBub3JtYWxs
eSBoYW5kbGVzIHRoaXMgY2xlYW51cCBpbiB0aGUgdG9wLWxldmVsCmV4ZWN1dGlvbiBwYXRoLCBi
dXQgd2hlbiBXQUlUIEZPUiBydW5zIHRocm91Z2ggU1BJIChQTC9wZ1NRTCksClByb2Nlc3NVdGls
aXR5IGlzIGNhbGxlZCBkaXJlY3RseSB3aXRob3V0IHRoZSBQb3J0YWxSdW5VdGlsaXR5CndyYXBw
ZXIsIHNvIHRoZSBwb3J0YWxTbmFwc2hvdCB3YXMgbmV2ZXIgY2xlYXJlZC4KCkZpeCBieSBjbGVh
cmluZyBBY3RpdmVQb3J0YWwtPnBvcnRhbFNuYXBzaG90IGFmdGVyIFBvcEFjdGl2ZVNuYXBzaG90
KCkKaW4gRXhlY1dhaXRTdG10KCksIG1hdGNoaW5nIHdoYXQgUG9ydGFsUnVuVXRpbGl0eSgpIGRv
ZXMuCgotLS0KIHNyYy9iYWNrZW5kL2NvbW1hbmRzL3dhaXQuYyB8IDExICsrKysrKysrKysrCiAx
IGZpbGUgY2hhbmdlZCwgMTEgaW5zZXJ0aW9ucygrKQoKZGlmZiAtLWdpdCBhL3NyYy9iYWNrZW5k
L2NvbW1hbmRzL3dhaXQuYyBiL3NyYy9iYWNrZW5kL2NvbW1hbmRzL3dhaXQuYwppbmRleCA4NWZj
ZDQ2My4uOGQyNDVkYmQgMTAwNjQ0Ci0tLSBhL3NyYy9iYWNrZW5kL2NvbW1hbmRzL3dhaXQuYwor
KysgYi9zcmMvYmFja2VuZC9jb21tYW5kcy93YWl0LmMKQEAgLTI0LDYgKzI0LDcgQEAKICNpbmNs
dWRlICJleGVjdXRvci9leGVjdXRvci5oIgogI2luY2x1ZGUgInBhcnNlci9wYXJzZV9ub2RlLmgi
CiAjaW5jbHVkZSAic3RvcmFnZS9wcm9jLmgiCisjaW5jbHVkZSAidGNvcC9wcXVlcnkuaCIKICNp
bmNsdWRlICJ1dGlscy9idWlsdGlucy5oIgogI2luY2x1ZGUgInV0aWxzL2d1Yy5oIgogI2luY2x1
ZGUgInV0aWxzL3BnX2xzbi5oIgpAQCAtMTQ2LDEwICsxNDcsMjAgQEAgRXhlY1dhaXRTdG10KFBh
cnNlU3RhdGUgKnBzdGF0ZSwgV2FpdFN0bXQgKnN0bXQsIERlc3RSZWNlaXZlciAqZGVzdCkKIAkg
KiBQbGFubmVkU3RtdFJlcXVpcmVzU25hcHNob3QoKSwgZXZlbiBpbiBhbiBhdG9taWMgY29udGV4
dCwgQ2FsbFN0bXQgaXMKIAkgKiBwcm9jZXNzZWQgd2l0aCBhIHNuYXBzaG90LiAgVGhhbmtmdWxs
eSwgd2UgY2FuIHBvcCB0aGlzIHNuYXBzaG90LAogCSAqIGJlY2F1c2UgUG9ydGFsUnVuVXRpbGl0
eSgpIGNhbiB0b2xlcmF0ZSB0aGlzLgorCSAqCisJICogV2hlbiBydW5uaW5nIGluc2lkZSBQTC9w
Z1NRTCwgdGhlIGFjdGl2ZQorCSAqIHBvcnRhbCBtYXkgaG9sZCBhIHBvaW50ZXIgdG8gdGhpcyBz
bmFwc2hvdCBpbiBwb3J0YWxTbmFwc2hvdC4gIFdlIG11c3QKKwkgKiBjbGVhciBpdCBzbyB0aGF0
IEVuc3VyZVBvcnRhbFNuYXBzaG90RXhpc3RzKCkgZG9lc24ndCB0cmlwIGFuIGFzc2VydGlvbgor
CSAqIHdoZW4gdGhlIG5leHQgUEwvcGdTUUwgc3RhdGVtZW50IHRyaWVzIHRvIHJlLWVzdGFibGlz
aCBhIHNuYXBzaG90LgogCSAqLwogCWlmIChBY3RpdmVTbmFwc2hvdFNldCgpKQorCXsKIAkJUG9w
QWN0aXZlU25hcHNob3QoKTsKIAorCQlpZiAoQWN0aXZlUG9ydGFsICYmIEFjdGl2ZVBvcnRhbC0+
cG9ydGFsU25hcHNob3QgIT0gTlVMTCkKKwkJCUFjdGl2ZVBvcnRhbC0+cG9ydGFsU25hcHNob3Qg
PSBOVUxMOworCX0KKwogCS8qCiAJICogQXQgc2Vjb25kLCBpbnZhbGlkYXRlIGEgY2F0YWxvZyBz
bmFwc2hvdCBpZiBhbnkuICBBbmQgd2Ugc2hvdWxkIGJlIGRvbmUKIAkgKiB3aXRoIHRoZSBwcmVw
YXJhdGlvbi4KLS0gCjIuNDMuMAoK
--000000000000cf2e70064efd6d31--