Daniel Westermann <daniel.westermann@xxxxxxxxxxxxxxxx> writes: > - if the above is correct why does PostgreSQL only write a partial file back to disk/wal? For me this still seems dangerous as potentially nobody will notice it In quiescent circumstances, Postgres wouldn't have written anything at all, and the file would have disappeared completely at server shutdown, and you would have gotten some sort of file-not-found error when you tried the "count(*)" after restarting. I hypothesize that you did an unclean shutdown leading to replaying some amount of WAL at restart, and that WAL included writing at least one block of the file (perhaps as a result of a hint-bit update, or some other not-user-visible maintenance operation, rather than anything you did explicitly). The WAL replay code will recreate the file if it doesn't exist on-disk --- this is important for robustness. Then you'd have a file that exists on-disk but is partially filled with empty pages, which matches the observed behavior. Depending on various details you haven't provided, this might be indistinguishable from a valid database state. > - PostgreSQL assumes that someone with write access to the files knows what she/he is doing. ok, but still, in the real world cases like this happen (for whatever reason) [ shrug... ] There's also an implied contract that you don't do "rm -rf /", or shoot the disk drive full of holes with a .45, or various other unrecoverable actions. We're not really prepared to expend large amounts of developer effort, or large amounts of runtime overhead, to detect such cases. (In particular, the fact that all-zero pages are a valid state is unfortunate from this perspective, but it's more or less forced by robustness concerns associated with table-extension behavior. Most users would not thank us for making table extension slower in order to issue a more intelligible error for examples like this one.) regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
