| From: | Dimitri Fontaine <dfontaine(at)hi-media(dot)com> |
|---|---|
| To: | cristina(dot)maier(at)yahoo(dot)com |
| Cc: | pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Problem with estimating pages for a table |
| Date: | 2009-05-14 10:35:00 |
| Message-ID: | 87octw9dm3.fsf@hi-media-techno.com |
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| Thread: | |
| Lists: | pgsql-hackers |
Hi,
Cristina M <cristina(dot)maier(at)yahoo(dot)com> writes:
> For each varchar column - I add an extra 4 bytes
> For each numeric column - I add an extra 8 bytes
> Add a 28 bytes row overhead.
>
> For example if i have a table with col1: integer, col2: varchar, col3 varchar, I will get:
> pages = (col1width + col2width + 4 + col3width + 4 + 28)* no. of rows
> / block size
You may find Greg Startk's presentation on the topic helpful:
http://wiki.postgresql.org/wiki/Image:How_Long_Is_a_String.pdf
Regards,
--
dim
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