Logical replication 'invalid memory alloc request size 1585837200' after upgrading to 17.5

PostgreSQL v17.5 (Ubuntu 17.5-1.pgdg24.04+1); Ubuntu 24.04.2 LTS (kernel 
6.8.0); x86-64

Good morning from DeepBlueCapital.  Soon after upgrading to 17.5 from 17.4, we 
started seeing logical replication failures with publisher errors like this:

   ERROR:  invalid memory alloc request size 1196493216

(the exact size varies).  Here is a typical log extract from the publisher:

2025-05-19 10:30:14 CEST \[1348336-465] remote\_production\_user\@blue DEBUG: 
00000: write FB03/349DEF90 flush FB03/349DEF90 apply FB03/349DEF90 reply\_time 
2025-05-19 10:30:07.467048+02
2025-05-19 10:30:14 CEST \[1348336-466] remote\_production\_user\@blue LOCATION: 
  ProcessStandbyReplyMessage, walsender.c:2431
2025-05-19 10:30:14 CEST \[1348336-467] remote\_production\_user\@blue DEBUG: 
00000: skipped replication of an empty transaction with XID: 207637565
2025-05-19 10:30:14 CEST \[1348336-468] remote\_production\_user\@blue CONTEXT: 
slot "jnb\_production", output plugin "pgoutput", in the commit callback, 
associated LSN FB03/349FF938
2025-05-19 10:30:14 CEST \[1348336-469] remote\_production\_user\@blue LOCATION: 
  pgoutput\_commit\_txn, pgoutput.c:629
2025-05-19 10:30:14 CEST \[1348336-470] remote\_production\_user\@blue DEBUG: 
00000: UpdateDecodingStats: updating stats 0x5ae1616c17a8 0 0 0 0 1 0 1 191
2025-05-19 10:30:14 CEST \[1348336-471] remote\_production\_user\@blue LOCATION: 
  UpdateDecodingStats, logical.c:1943
2025-05-19 10:30:14 CEST \[1348336-472] remote\_production\_user\@blue DEBUG: 
00000: found top level transaction 207637519, with catalog changes
2025-05-19 10:30:14 CEST \[1348336-473] remote\_production\_user\@blue LOCATION: 
  SnapBuildCommitTxn, snapbuild.c:1150
2025-05-19 10:30:14 CEST \[1348336-474] remote\_production\_user\@blue DEBUG: 
00000: adding a new snapshot and invalidations to 207616976 at FB03/34A1AAE0
2025-05-19 10:30:14 CEST \[1348336-475] remote\_production\_user\@blue LOCATION: 
  SnapBuildDistributeSnapshotAndInval, snapbuild.c:915
2025-05-19 10:30:14 CEST \[1348336-476] remote\_production\_user\@blue ERROR: 
XX000: invalid memory alloc request size 1196493216

If I'm reading it right, things go wrong on the publisher while preparing the 
message, i.e. it's not a subscriber problem.

This particular instance was triggered by a large number of catalog 
invalidations: I dumped what I think is the relevant WAL with "pg_waldump -s 
FB03/34A1AAE0 -p 17/main/ --xid=207637519" and the output was a single long line:

rmgr: Transaction len (rec/tot):  10665/ 10665, tx:  207637519, lsn: 
FB03/34A1AAE0, prev FB03/34A1A8C8, desc: COMMIT 2025-05-19 08:10:12.880599 CEST; 
dropped stats: 2/17426/661557718 2/17426/661557717 2/17426/661557714 
2/17426/661557678 2/17426/661557677 2/17426/661557674 2/17426/661557673 
2/17426/661557672 2/17426/661557669 2/17426/661557618 2/17426/661557617 
2/17426/661557614; inval msgs: catcache 80 catcache 79 catcache 80 catcache 79 
catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 
catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 catcache 32 catcache 55 
catcache 54 catcache 55 catcache 54 catcache 55 catcache 54 catcache 80 catcache 
79 catcache 80 catcache 79 catcache 55 catcache 54 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 32 catcache 55 catcache 54 catcache 55 catcache 54 catcache 
55 catcache 54 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 
catcache 63 catcache 63 catcache 55 catcache 54 catcache 80 catcache 79 catcache 
80 catcache 79 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 catcache 
6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 32 catcache 55 catcache 54 catcache 55 catcache 54 catcache 55 catcache 
54 catcache 80 catcache 79 catcache 80 catcache 79 catcache 55 catcache 54 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 
catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 32 catcache 55 catcache 54 
catcache 55 catcache 54 catcache 55 catcache 54 catcache 63 catcache 63 catcache 
63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 
catcache 63 catcache 63 catcache 55 catcache 54 catcache 32 catcache 7 catcache 
6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 55 catcache 54 catcache 80 catcache 79 catcache 80 catcache 
79 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 
catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 7 catcache 
6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 32 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 80 catcache 79 
catcache 80 catcache 79 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 55 catcache 54 catcache 32 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 55 catcache 54 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 55 catcache 54 catcache 80 catcache 79 catcache 80 catcache 79 catcache 
63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 catcache 63 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 
catcache 32 catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 55 catcache 54 catcache 80 
catcache 79 catcache 80 catcache 79 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 
catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 catcache 6 catcache 7 
catcache 6 catcache 55 catcache 54 snapshot 2608 relcache 661557614 snapshot 
1214 relcache 661557617 relcache 661557618 relcache 661557617 snapshot 2608 
relcache 661557617 relcache 661557618 relcache 661557614 snapshot 2608 snapshot 
2608 relcache 661557669 snapshot 1214 relcache 661557672 relcache 661557673 
relcache 661557672 snapshot 2608 relcache 661557672 relcache 661557673 relcache 
661557669 snapshot 2608 relcache 661557669 snapshot 2608 relcache 661557674 
snapshot 1214 relcache 661557677 relcache 661557678 relcache 661557677 snapshot 
2608 relcache 661557677 relcache 661557678 relcache 661557674 snapshot 2608 
snapshot 2608 relcache 661557714 snapshot 1214 relcache 661557717 relcache 
661557718 relcache 661557717 snapshot 2608 relcache 661557717 relcache 661557718 
relcache 661557714 snapshot 2608 relcache 661557714 relcache 661557718 relcache 
661557717 snapshot 2608 relcache 661557717 snapshot 2608 snapshot 2608 snapshot 
2608 relcache 661557714 snapshot 2608 snapshot 1214 relcache 661557678 relcache 
661557677 snapshot 2608 relcache 661557677 snapshot 2608 snapshot 2608 snapshot 
2608 relcache 661557674 snapshot 2608 snapshot 1214 relcache 661557673 relcache 
661557672 snapshot 2608 relcache 661557672 snapshot 2608 snapshot 2608 snapshot 
2608 relcache 661557669 snapshot 2608 snapshot 1214 relcache 661557618 relcache 
661557617 snapshot 2608 relcache 661557617 snapshot 2608 snapshot 2608 snapshot 
2608 relcache 661557614 snapshot 2608 snapshot 1214

While it is long, it doesn't seem to merit allocating anything like 1GB of 
memory.  So I'm guessing that postgres is miscalculating the required size somehow.

If I skip over this LSN, for example by dropping the subscription and recreating 
it anew, then things go fine for a while before hitting another "invalid memory 
alloc request", i.e. it wasn't just a one-off.  On the other hand, after 
downgrading to 17.4, subscribers spontaneously recovered and the issue has gone 
way.  Since I didn't skip over the last LSN of this kind, presumably 17.4 
successfully serialized a message for the same problematic bit of WAL that 
caused 17.5 to blow up, which suggests a regression between 17.4 and 17.5.

Best wishes, Duncan.