From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
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To: | Neto pr <netopr9(at)gmail(dot)com> |
Cc: | postgres performance list <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Pageinspect bt_metap help |
Date: | 2017-09-19 01:07:26 |
Message-ID: | CAH2-WzmvNvC4FGmixpMAFcq3GiPxMiZqw9-_4Gn_J34rAxg1NQ@mail.gmail.com |
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Lists: | pgsql-performance |
On Mon, Sep 18, 2017 at 7:31 AM, Neto pr <netopr9(at)gmail(dot)com> wrote:
> In my example, the values of fast_root, fast_root are equal to root, level,
> I believe that due to the newly created index and no delete operations
> occurred in the table.
Fast root and true root will probably never be different, even when
there are many deletions, including page deletions by VACUUM. As I
understand it, the fast root thing is for a fairly rare, though still
important edge case. It's a way of working around the fact that a
B-Tree can never become shorter due to the locking protocols not
allowing it. We can instead just pretend that it's shorter, knowing
that upper levels don't contain useful information.
--
Peter Geoghegan
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