From 1e421e723831bc12f4ab23aa2ede8520bb9c072d Mon Sep 17 00:00:00 2001 From: Jacob Champion Date: Mon, 23 Feb 2026 15:28:32 -0800 Subject: [PATCH v2] pg_upgrade: Use max_protocol_version=3.0 for older servers The grease patch in 4966bd3ed found its first problem: prior to the February 2018 patch releases, no server knew how to negotiate protocol versions, so pg_upgrade needs to take that into account when speaking to those older servers. This will be true even after the grease feature is reverted; we don't need anyone to trip over this again in the future. Backpatch so that all supported versions of pg_upgrade can gracefully handle an update to the default protocol version. (This is needed for any distributions that link older binaries against newer libpqs, such as Debian.) Branches prior to 18 need an additional version check, for the existence of max_protocol_version. Per buildfarm member crake. Discussion: https://postgr.es/m/CAOYmi%2B%3D4QhCjssfNEoZVK8LPtWxnfkwT5p-PAeoxtG9gpNjqOQ%40mail.gmail.com Backpatch-through: 14 --- src/bin/pg_upgrade/pg_upgrade.h | 1 + src/bin/pg_upgrade/dump.c | 6 +++++- src/bin/pg_upgrade/server.c | 2 ++ src/bin/pg_upgrade/version.c | 31 +++++++++++++++++++++++++++++++ 4 files changed, 39 insertions(+), 1 deletion(-) diff --git a/src/bin/pg_upgrade/pg_upgrade.h b/src/bin/pg_upgrade/pg_upgrade.h index e2b99b49fab..5ad693eaa70 100644 --- a/src/bin/pg_upgrade/pg_upgrade.h +++ b/src/bin/pg_upgrade/pg_upgrade.h @@ -482,6 +482,7 @@ unsigned int str2uint(const char *str); /* version.c */ bool jsonb_9_4_check_applicable(ClusterInfo *cluster); +bool protocol_negotiation_supported(const ClusterInfo *cluster); void old_9_6_invalidate_hash_indexes(ClusterInfo *cluster, bool check_mode); diff --git a/src/bin/pg_upgrade/dump.c b/src/bin/pg_upgrade/dump.c index 29fb45b9289..b14c4ce0ee2 100644 --- a/src/bin/pg_upgrade/dump.c +++ b/src/bin/pg_upgrade/dump.c @@ -21,9 +21,10 @@ generate_old_dump(void) /* run new pg_dumpall binary for globals */ exec_prog(UTILITY_LOG_FILE, NULL, true, true, - "\"%s/pg_dumpall\" %s --globals-only --quote-all-identifiers " + "\"%s/pg_dumpall\" %s%s --globals-only --quote-all-identifiers " "--binary-upgrade %s -f \"%s/%s\"", new_cluster.bindir, cluster_conn_opts(&old_cluster), + protocol_negotiation_supported(&old_cluster) ? "" : " -d \"max_protocol_version=3.0\"", log_opts.verbose ? "--verbose" : "", log_opts.dumpdir, GLOBALS_DUMP_FILE); @@ -43,6 +44,9 @@ generate_old_dump(void) initPQExpBuffer(&connstr); appendPQExpBufferStr(&connstr, "dbname="); appendConnStrVal(&connstr, old_db->db_name); + if (!protocol_negotiation_supported(&old_cluster)) + appendPQExpBufferStr(&connstr, " max_protocol_version=3.0"); + initPQExpBuffer(&escaped_connstr); appendShellString(&escaped_connstr, connstr.data); termPQExpBuffer(&connstr); diff --git a/src/bin/pg_upgrade/server.c b/src/bin/pg_upgrade/server.c index b223d5afddf..107e2676397 100644 --- a/src/bin/pg_upgrade/server.c +++ b/src/bin/pg_upgrade/server.c @@ -71,6 +71,8 @@ get_db_conn(ClusterInfo *cluster, const char *db_name) appendPQExpBufferStr(&conn_opts, " host="); appendConnStrVal(&conn_opts, cluster->sockdir); } + if (!protocol_negotiation_supported(cluster)) + appendPQExpBufferStr(&conn_opts, " max_protocol_version=3.0"); conn = PQconnectdb(conn_opts.data); termPQExpBuffer(&conn_opts); diff --git a/src/bin/pg_upgrade/version.c b/src/bin/pg_upgrade/version.c index 2de6dffccda..276ead84e3f 100644 --- a/src/bin/pg_upgrade/version.c +++ b/src/bin/pg_upgrade/version.c @@ -28,6 +28,37 @@ jsonb_9_4_check_applicable(ClusterInfo *cluster) return false; } +/* + * Older servers can't support newer protocol versions, so their connection + * strings will need to lock max_protocol_version to 3.0. + */ +bool +protocol_negotiation_supported(const ClusterInfo *cluster) +{ + /* + * Back-branch-specific complication: for libpq versions prior to PG18, + * max_protocol_version isn't supported. But we also don't need to worry + * about newer protocol versions being used in that case, so just lie and + * return true. + * + * (Checking for a libpq version that's newer than this branch looks very + * strange, but distributions are allowed to link older pg_upgrade + * binaries against the newest release of libpq.) + */ + if (PQlibVersion() < 180000) + return true; + + /* + * The February 2018 patch release (9.3.21, 9.4.16, 9.5.11, 9.6.7, and + * 10.2) added support for NegotiateProtocolVersion. But ClusterInfo only + * has information about the major version number. To ensure we can still + * upgrade older unpatched servers, just assume anything prior to PG11 + * can't negotiate. It's not possible for those servers to make use of + * newer protocols anyway, so nothing is lost. + */ + return (GET_MAJOR_VERSION(cluster->major_version) >= 1100); +} + /* * old_9_6_invalidate_hash_indexes() * 9.6 -> 10 -- 2.34.1