Currently, database OIDs, relfilenodes, and tablespace OIDs can all change when a cluster is upgraded using pg_upgrade. It seems better to preserve them, because (1) it makes troubleshooting pg_upgrade easier, since you don't have to do a lot of work to match up files in the old and new clusters, (2) it allows 'rsync' to save bandwidth when used to re-sync a cluster after an upgrade, and (3) if we ever encrypt or sign blocks, we would likely want to use a nonce that depends on these values.
This patch only arranges to preserve relfilenodes and tablespace OIDs. The task of preserving database OIDs is left for another patch, since it involves some complexities that don't exist in these cases.
Database OIDs have a similar issue, but there are some tricky points in that case that do not apply to these cases, so that problem is left for another patch.
Shruthi KC, based on an earlier patch from Antonin Houska, reviewed and with some adjustments by me.
9a974cbcba pg_upgrade: Preserve relfilenodes and tablespace OIDs.
src/backend/bootstrap/bootparse.y | 3 +-
src/backend/catalog/heap.c | 63 ++++++++++---
src/backend/catalog/index.c | 23 ++++-
src/backend/commands/tablespace.c | 17 +++-
src/backend/utils/adt/pg_upgrade_support.c | 44 +++++++++
src/bin/pg_dump/pg_dump.c | 104 ++++++++++++++-------
src/bin/pg_dump/pg_dumpall.c | 3 +
src/bin/pg_upgrade/info.c | 31 +-----
src/bin/pg_upgrade/pg_upgrade.c | 13 +--
src/bin/pg_upgrade/pg_upgrade.h | 10 +-
src/bin/pg_upgrade/relfilenode.c | 6 +-
src/include/catalog/binary_upgrade.h | 5 +
src/include/catalog/catversion.h | 2 +-
src/include/catalog/heap.h | 3 +-
src/include/catalog/pg_proc.dat | 16 ++++
.../spgist_name_ops/expected/spgist_name_ops.out | 12 ++-
16 files changed, 247 insertions(+), 108 deletions(-)