On 20 February 2017 at 10:27, Amit Kapila <amit.kapil...@gmail.com> wrote: > On Mon, Feb 20, 2017 at 3:01 PM, Simon Riggs <si...@2ndquadrant.com> wrote: >> On 20 February 2017 at 09:15, Amit Kapila <amit.kapil...@gmail.com> wrote: >>> On Mon, Feb 20, 2017 at 7:26 AM, Masahiko Sawada <sawada.m...@gmail.com> >>> wrote: >>>> On Fri, Feb 17, 2017 at 3:41 AM, Robert Haas <robertmh...@gmail.com> wrote: >>>>> On Thu, Feb 16, 2017 at 6:17 AM, Simon Riggs <si...@2ndquadrant.com> >>>>> wrote: >>>>>> On 15 February 2017 at 08:07, Masahiko Sawada <sawada.m...@gmail.com> >>>>>> wrote: >>>>>>> It's a bug. Attached latest version patch, which passed make check. >> >>>>>> 2. The current btree vacuum code requires 2 vacuums to fully reuse >>>>>> half-dead pages. So skipping an index vacuum might mean that second >>>>>> index scan never happens at all, which would be bad. >>>>> >>>>> Maybe. If there are a tiny number of those half-dead pages in a huge >>>>> index, it probably doesn't matter. Also, I don't think it would never >>>>> happen, unless the table just never gets any more updates or deletes - >>>>> but that case could also happen today. It's just a matter of >>>>> happening less frequently. >>>> >>> >>> Yeah thats right and I am not sure if it is worth to perform a >>> complete pass to reclaim dead/deleted pages unless we know someway >>> that there are many such pages. >> >> Agreed.... which is why >> On 16 February 2017 at 11:17, Simon Riggs <si...@2ndquadrant.com> wrote: >>> I suggest that we store the number of half-dead pages in the metapage >>> after each VACUUM, so we can decide whether to skip the scan or not. >> >> >>> Also, I think we do reclaim the >>> complete page while allocating a new page in btree. >> >> That's not how it works according to the README at least. >> > > I am referring to code (_bt_getbuf()->if (_bt_page_recyclable(page))), > won't that help us in reclaiming the space?
Not unless the README is incorrect, no. That section of code is just a retest of pages retrieved from FSM; they aren't even added there until two scans have occurred and even then it may not be possible to recycle. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers