Обсуждение: pgsql: Further harden nbtree posting split code.

Further harden nbtree posting split code.

Add more defensive checks around posting list split code.  These should
detect corruption involving duplicate table TIDs earlier and more
reliably than any existing check.

Follow up to commit 8f72bbac.

Discussion: https://postgr.es/m/CAH2-WzkrSY_kjyd1_M5xJK1uM0govJXMxPn8JUSvwcUOiHuWVw@mail.gmail.com
Backpatch: 13-, where nbtree deduplication was introduced.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/a5213adf3d351a31c5f5eae1a756a9d3555dc31c

Modified Files
--------------
src/backend/access/nbtree/nbtinsert.c | 23 +++++++++++++++++++++--
src/backend/access/nbtree/nbtsearch.c | 17 +++++++++++++++++
2 files changed, 38 insertions(+), 2 deletions(-)