Re: Free space mapping (was Re: Multi-Versions and Vacuum) - Mailing list pgsql-general

From Mark Kirkwood
Subject Re: Free space mapping (was Re: Multi-Versions and Vacuum)
Date
Msg-id 3D6C06F4.8040201@slingshot.co.nz
Whole thread Raw
In response to Re: Free space mapping (was Re: Multi-Versions and Vacuum)  (Mark Kirkwood <markir@slingshot.co.nz>)
List pgsql-general
Tom Lane wrote:

>It doesn't need a lot of examination in my mind: the cause is surely
>growth of the index on the toast table.  Since that index's first column
>is the OID assigned to the toast item, the range of indexed values tends
>to shift over time, causing the leftmost parts of the index btree to
>become sparsely populated and eventually empty.  Since we don't
>currently have code to collapse out empty pages in a btree, the index
>grows during continued update activity, even if the total amount of data
>you're storing isn't growing.  This is quite unrelated to the free space
>map --- indexes don't use the FSM.
>
>
>
hmmm, good point - I thought the toast table was growing too, but I will
check this.

regards

Mark




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