On 11/23/21 05:49, Andy Fan wrote: > > > I think at this thread[1], which claimed to get this issue even after > > commit, I haven't tried it myself though. > > > > [1] > > https://www.postgresql.org/message-id/flat/ea6485e3-98d0-24a7-094c-87f9d5f9b18f%40amazon.com#4cfe7217c829419b769339465e8c2915 > > <https://www.postgresql.org/message-id/flat/ea6485e3-98d0-24a7-094c-87f9d5f9b18f%40amazon.com#4cfe7217c829419b769339465e8c2915> > > > > I did try, and I haven't been able to reproduce that behavior (on > master, at least). > > > I agree with this, the commit would flush the xlog and persist the change.
On that older thread, there were exact reproductions in the first email from Vini - two of them - available here: https://gist.github.com/vinnix/2fe148e3c42e11269bac5fcc5c78a8d1 Nathan help me realize a mistake I've made here. The second reproduction involved having psql run nextval() inside of an explicit transaction. I had assumed that the transaction would be committed when psql closed the session without error. This is because in Oracle SQLPlus (my original RDBMS background), the "exitcommit" setting has a default value giving this behavior. This was a silly mistake on my part. When PostgreSQL psql closes the connection with an open transaction, it turns out that the PostgreSQL server will abort the transaction rather than committing it. (Oracle DBAs be-aware!) Nonetheless, Vini's first reproduction did not make this same mistake. It involved 10 psql sessions in parallel using implicit transactions, suspending I/O (via the linux device mapper), and killing PG while the I/O is suspended. Given my mistake on the second repro, I want to look a little closer at this first reproduction and revisit whether it's actually demonstrating a corner case where one could claim that durability isn't being handled correctly - that "COMMIT" is returning successfully to the application, and yet the sequence numbers are being repeated. Maybe there's something involving the linux I/O path coming into play here. -Jeremy -- http://about.me/jeremy_schneider
