adding a nullable col could rewrite the whole table? - Mailing list pgsql-general

From Scara Maccai
Subject adding a nullable col could rewrite the whole table?
Date
Msg-id 850000.2913.qm@web24603.mail.ird.yahoo.com
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Responses Re: adding a nullable col could rewrite the whole table?
List pgsql-general
Hi all,

in the docs I read:

"Adding a column with a non-null default [...] will require the entire table to be rewritten"

I guess that that can't be read as "you can always assume that adding a nullable column to a table won't rewrite the
wholetable". 

I'm asking because since the page layout includes a null bitmap that
"If it is present it begins just after the fixed header and occupies enough bytes to have one bit per data column", I
guessthat when all the bits in the bitmap are used when I add a column (even a nullable one) the table gets rewritten
(toadd a new byte to the nullable bitmap); is this true? 





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