Most importantly, remove optimization in LogicalRepSyncTableStart that skips the normal walrcv_startstreaming/endstreaming dance. The optimization is not critically important for production uses anyway, since it only fires in cases with no activity, and saves an uninteresting amount of work even then. Critically, it obscures bugs by hiding the interesting code path from test cases.
Also: in GetSubscriptionRelState, remove pointless relation open; access pg_subscription_rel->srsubstate with GETSTRUCT as is typical rather than SysCacheGetAttr; remove unused 'missing_ok' argument. In wait_for_relation_state_change, use explicit catalog snapshot invalidation rather than obscurely (and expensively) through GetLatestSnapshot. In various places: sprinkle comments more liberally and rewrite a number of them. Other cosmetic code improvements.
No backpatch, since no bug is being fixed here.
Author: Álvaro Herrera
b05fe7b442 Review logical replication tablesync code
src/backend/catalog/pg_subscription.c | 27 +--
src/backend/replication/logical/relation.c | 3 +-
src/backend/replication/logical/tablesync.c | 261 +++++++++++++---------------
src/backend/replication/logical/worker.c | 15 +-
src/include/catalog/pg_subscription_rel.h | 3 +-
5 files changed, 131 insertions(+), 178 deletions(-)