What is the difference in storage between a blank string and null?

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I'm doing some testing on how to decrease our database size as I work on a
partitioning scheme.

I have found that if I have the database store all empty strings as nulls,
I
get a significant savings over saving them as blank strings (i.e. '').
Below is an example of savings I am seeing for the same table:

In my test case, storing empty strings  give me a table size of 20,635,648
Storing empty strings as nulls gives me a table size of: 5,742,592.

As you can see, storing empty strings as nulls is saving me approximately
72% on this table.  So, I am wanting to understand what Postgres is doing
differently with the nulls.  Would someone kindly enlighten me on this.

(P.S. I am using a nullif(trim(column),'') in my partition and view rules
to
store the nulls, and coalesce(column,'') to give my application the data
back without nulls.)

Thanks,

Chris

PG 8.1

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I'm doing some testing on how to decrease our database size as I work
on a partitioning scheme.&nbsp; <br><br>I have found that if I have the
database store all empty strings as nulls, I get a significant savings
over saving them as blank strings (i.e. &#39;&#39;).&nbsp; Below is an
example of savings I am seeing for the same table:<br>
<br>In my test case, storing empty strings&nbsp; give me a table size of
20,635,648<br><meta http-equiv="CONTENT-TYPE" content="text/html;
charset=utf-8"><title></title><meta name="GENERATOR"
content="OpenOffice.org 2.4  (Linux)">Storing empty strings as nulls gives
me a table size of: 5,742,592.<br>
<br>As you can see, storing empty strings as nulls is saving me
approximately 72% on this table.&nbsp; So, I am wanting to understand what
Postgres is doing differently with the nulls.&nbsp; Would someone kindly
enlighten me on this.<br>
<br>(P.S. I am using a nullif(trim(column),&#39;&#39;) in my partition and
view rules to store the nulls, and coalesce(column,&#39;&#39;) to give my
application the data back without nulls.)<br><br>Thanks,<br><br>Chris<br>
<br>PG 8.1<br clear="all"><br>-- <br>Tired of HIGH Gas prices?&nbsp; Visit
<a href="http://colafuelguy.mybpi.com">http://colafuelguy.mybpi.com</a>
to
start saving at the pump no matter where you live!<br>

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