Re: Default fill factor for tables? - Mailing list pgsql-general

From Roberts, Jon
Subject Re: Default fill factor for tables?
Date
Msg-id 1A6E6D554222284AB25ABE3229A92762E9A74C@nrtexcus702.int.asurion.com
Whole thread Raw
In response to Re: Default fill factor for tables?  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: Default fill factor for tables?
List pgsql-general
> Roberts, Jon escribió:
>
> > Why would you set the fillfactor to anything other than 100 for a
> > PostgreSQL table?
>
> To favor HOT updates.
>
> --

I can find very little information on hot updates but I found this:
http://archives.postgresql.org/pgsql-patches/2006-11/msg00059.php

It states, "This design optimizies the updates when none of the index columns are modified and length of the tuple
remainsthe same after update."   

How can a row's length change?  I think it must mean the size (in bytes) of the row remains the same.

If this is the constraint, then I still don't see the benefit.  If the size can vary, I can see the benefit because the
newcolumn value may be larger than the old value thus needing the space.   

Why isn't the hot update documented in these locations?
http://www.postgresql.org/docs/8.3/interactive/sql-createtable.html
http://www.postgresql.org/docs/8.3/interactive/sql-update.html
http://www.postgresql.org/docs/8.3/interactive/sql-altertable.html



Jon


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