The optimizer stats are not lost on crash or promote actually; these are stored in pg_statistic (not in the stats collector) and *are* part of regular "data". ...
I think it's pretty common misunderstanding -- it's not easy to see the boundary between pg_statistic and pg_stat_* tables.
Thanks for this. I thought I remembered being corrected on this before (probably on this very list) and just came to think of it at the end of my last message.
So what, exactly ARE the pg_stat_* tables?
Activity statistics, collected by the stats collector process.
Is that the data stored in the files in stats_temp_directory?
Yes.
How do they differ from pg_statistic?
Those in pg_statistic are data statistics. They're used by the planner, and collected by the ANALYZE SQL command.