Alvaro Herrera <alvherre@xxxxxxxxxxxxxxxxx> writes: > Now 40 mins walking those pages to figure out that they need to be > truncated, I concede that it's too much. Maybe we shouldn't be doing a > backwards scan; perhaps this breaks the OS readahead and make it even > slower. That's very possible, since a backwards scan is guaranteed to destroy any rotational positioning the OS has done --- you'll have to wait at least one disk rotation for each page, whereas a forward scan could hope to do better than that. Maybe we could do this along with my idea of incremental truncation. Scan the last K pages of the relation *forwards*, truncate as appropriate, repeat, until finding a nonempty page. Choosing the max value of K might be a bit tricky. 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
