Ensure that vacuum will always clean up the pending-insertions list of a GIN index (Masahiko Sawada)
This is necessary to ensure that dead index entries get removed. The old code got it backwards, allowing vacuum to skip the cleanup if some other process were running cleanup concurrently, thus risking invalid entries being left behind in the index.
Fix mishandling of empty uncompressed posting list pages in GIN indexes (Sivasubramanian Ramasubramanian, Alexander Korotkov)
This could result in an assertion failure after pg_upgrade of a pre-9.4 GIN index (9.4 and later will not create such pages).
Add predicate locking for hash, GiST and GIN indexes (Shubham Barai)
This reduces the likelihood of serialization conflicts in serializable-mode transactions.
Avoid deadlock between GIN vacuuming and concurrent index insertions (Alexander Korotkov, Andrey Borodin, Peter Geoghegan)
This change partially reverts a performance improvement, introduced in version 10.0, that attempted to reduce the number of index pages locked during deletion of a GIN posting tree page. That's now been found to lead to deadlocks, so we've removed it pending closer analysis.
Avoid deadlock between hot-standby queries and replay of GIN index page deletion (Alexander Korotkov)
Prevent empty GIN index pages from being reclaimed too quickly, causing failures of concurrent searches (Andrey Borodin, Alexander Korotkov)