On Mon, Mar 19, 2018 at 8:45 AM, Kyotaro HORIGUCHI < horiguchi.kyot...@lab.ntt.co.jp> wrote:
> At Mon, 19 Mar 2018 11:12:58 +0900, Masahiko Sawada <sawada.m...@gmail.com> > wrote in <CAD21AoAB8tQg9xwojupUJjKD=fmhtx6thdependdhftvlwc...@mail.gm > ail.com> > > require the bulk-delete method of scanning whole index and of logging > > WAL. But it leads some extra overhead. With this patch we no longer > > need to depend on the full scan on b-tree index. This might be useful > > for a future when we make the bulk-delete of b-tree index not scan > > whole index. > > Perhaps I'm taking something incorrectly, but is it just the > result of skipping 'maybe needed' scans without condiering the > actual necessity? > > I also don't like extra WAL logging, but it happens once (or > twice?) per vaccum cycle (for every index). In my version of patch WAL logging doesn't happen every vacuum cycle. WAL-logging of meta-page happens only in two cases: 1) After first vacuum which didn't delete any heap tuples. I.e. after we switch from update workload to append-only workload. 2) During append-only workload when cleanup is triggered (either deleted pages become recyclable or statistics considered as stalled). Typically in both update and append-only workloads, WAL logging isn't happening during vacuum cycle. Masahiko Sawada has proposed to update meta-information during btbulkdelete [1]. That would lead to WAL logging in almost very vacuum cycle. I was slightly opposed to that saying that this overhead need to be tested [2]. However this concern is not related to current shape of my version of patch. > On the other hand I > want to put the on-the-fly upgrade path out of the ordinary > path. (Reviving the pg_upgrade's custom module?) > I don't know. Previously, we successfully did on-fly upgrade of GIN posting lists. Our pg_upgrade machinery is probably already very complicated and overloaded. Should we burden it with upgrade of every meta-page of every B-tree index assuming that we can handle it very well inside B-tree itself on the fly? 1. https://www.postgresql.org/message-id/CAD21AoBpD1zZ8%2BkmN-6sCb0WkVe7X4ON31Oy-JsgafOC5DOYxA%40mail.gmail.com 2. https://www.postgresql.org/message-id/CAPpHfdsiDUXKXzfc%2BNHrAvjv3nekR-4WfwgSNBBXJYxuhBcCFA%40mail.gmail.com ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
