On Tue, 2023-01-17 at 15:22 +0000, HECTOR INGERTO wrote: > > Another case: a transaction COMMITs, and a slightly later transaction reads > > the data > > and sets a hint bit. If the snapshot of the file system with the data > > directory in it > > is slightly later than the snapshot of the file system with "pg_wal", the > > COMMIT might > > not be part of the snapshot, but the hint bit could be. > > > > Then these uncommitted data could be visible if you recover from the > > snapshot. > > Thank you all. I have it clearer now. > > As a last point. Making the snapshot to the WAL dataset first or last would > make any difference?
Imagine you run DROP TABLE. During the implicit COMMIT at the end of the statement, the files behind the table are deleted. If the snapshot of "pg_wal" is earlier than the snapshot of the data files, you end up with a table that is not yet dropped, but the files are gone. I won't try to find an example if you now ask what if no checkpoint ends between the statements, the snapshot on "pg_wal" is earlier and we don't run DROP TABLE. Why do you go to all this effort rather than performing a correct backup? Yours, Laurenz Albe
