Scariest patch tournament, PostgreSQL 11 edition

PostgreSQL hackers and community at large,

In the spirit of the season, the Release Management Team would like to
gather your thoughts on Fear, Risk and Data Corruption for features in
PostgreSQL 11. What patch or patches committed in this cycle do you
think have the highest probability of causing problems of any sort for
users?

The poll is not open yet; we'll give a couple of weeks for you to
collect your thoughts, reflect back on the highly active development
cycle, and go over the long list of Postgres 11 commits to define your
candidates.

The PostgreSQL 11 users-to-be will wholeheartedly thank you.

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This, of course, is a bit tongue-in-cheek. However, going back to
Peter's thoughts[1] about the previous time we did it: the main point of
this poll is to crowd-source the question of where should testing and
post-commit review efforts focus on the most. Please keep this in mind
when considering your answers.

[1] https://www.postgresql.org/message-id/CAM3SWZQi7b4JUvySrU6j_zJOZkvDyNqg7ZkDcjxWHAbc86aw-Q@mail.gmail.com

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Álvaro Herrera