From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | Leonardo F <m_lists(at)yahoo(dot)it>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: access method: are disk pages mandatory? |
Date: | 2010-06-23 18:24:02 |
Message-ID: | 25600.1277317442@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 23/06/10 18:17, Leonardo F wrote:
>> I'm not getting it: am I supposed to use the "disk page format" when
>> writing an index access method, or it's just a "good practice" because
>> it makes the handling easier? Given the docs it looks "recommended",
>> but the comment on the code sounds more "mandatory".
> It's recommened because it makes life easier. Even if you don't use the
> normal page format, I think you need to have the LSN at the beginning of
> the page. The rest is up to you.
The bufpage.h comment is ancient and might not be 100% gospel anymore.
However, I believe the buffer manager does assume that any page in
shared buffers has a standard page header including LSN. It definitely
assumes there's an LSN, and I think we have validity checks on the other
page header fields somewhere inside ReadBuffer. You don't however need
to use the item-and-item-pointer-array structure if it's not useful to
you.
regards, tom lane
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