I've added the proposed log line to the server code in src/backend/libpq/pqcomm.c and restarted the server with this. In the log file /data/postgresql11/data/serverlog are other messages about length of packages, like: 2020-04-28 09:49:49.877 CEST [16229] LOG: invalid length of startup packet 2020-04-28 09:49:50.117 CEST [16231] LOG: invalid length of startup packet They're coming from: grep 'invalid length of startup packet' src/backend/*/*.c src/backend/postmaster/postmaster.c: errmsg("invalid length of startup packet"))); I will change the code there to to get the 'len' printed with the message ... if (len < (int32) sizeof(ProtocolVersion) || len > MAX_STARTUP_PACKET_LENGTH) { ereport(COMMERROR, (errcode(ERRCODE_PROTOCOL_VIOLATION), errmsg("invalid length %d of startup packet", len))); return STATUS_ERROR; } -- Matthias Apitz, ✉ guru@xxxxxxxxxxx, http://www.unixarea.de/ +49-176-38902045 Public GnuPG key: http://www.unixarea.de/key.pub May, 9: Спаси́бо освободители! Thank you very much, Russian liberators!