From: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Gregory Stark <gsstark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Variable length varlena headers redux |
Date: | 2007-02-13 15:30:08 |
Message-ID: | 45D1D980.4050109@enterprisedb.com |
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Lists: | pgsql-hackers |
Bruce Momjian wrote:
> Heikki Linnakangas wrote:
>> We would still require all datums with a 4-byte header to be 4-byte
>> aligned, right? When reading, you would first check if it's a compressed
>> or uncompressed header. If compressed, read the 1 byte header, if
>> uncompressed, read the 4-byte header and do htonl or bitshifting. No
>> need to do htonl or bitshifting on unaligned datums.
>
> I am not sure how to handle the alignment issue. If we require 1-byte
> headers to be 4-byte aligned, we lose a lot of the benefits of the
> 1-byte header.
Why would we require that?
I don't see a problem with having 4-byte header 4-byte aligned, and
1-byte headers not aligned. The first access to the header is to check
if it's a 4 or 1 byte header. That's a 1 byte wide access, requiring no
alignment. After that you know which one it is.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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