Curt Sampson <[EMAIL PROTECTED]> writes: > Oracle9i has a new feature called a "flashback query," which uses the > information in the rollback segements to let you query the database > in a previous state. (I.e., "select such and such from this table as > of two hours ago.") Postgres could do this using the older copies of > rows as well,
Yeah, good ol' time-travel. This was built into Postgres in Berkeley days, and later ripped out for performance reasons. > though the performance often wouldn't be pretty, since > your indexes become useless, I believe. (Don't they point to only the > latest copy of a row?) No. If they did, they'd not work under MVCC. > BTW, why exactly do we pre-create log segments, anyway? Partly because the logic is designed to work in the PITR case, but mostly because we don't want to suffer an out-of-disk-space condition while we are in the midst of using a log segment. > This seems to imply to me that fdatasync will, when synchronizing the > data blocks of a file, not necessarially synchronize the indirect > blocks, which seems a little...odd. The comment is being paranoid about whether fdatasync is correctly implemented everywhere. Whether you consider this worry justified or not is academic, since the possible out-of-disk-space failure mode is reason enough to do it anyway. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])