On Tue, Jul 18, 2023 at 04:50:25PM +0800, Pandora wrote: > I found that starting from version 9.5, PostgreSQL will do fsync on > the entire data directory after DB crash. Here's a question: if I > have FPW = on, why is this step still necessary?
Yes, see around the call of SyncDataDirectory() in xlog.c: * - There might be data which we had written, intending to fsync it, but * which we had not actually fsync'd yet. Therefore, a power failure in * the near future might cause earlier unflushed writes to be lost, even * though more recent data written to disk from here on would be * persisted. To avoid that, fsync the entire data directory. -- Michael
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