Re: [HACKERS] PATCH: pageinspect / add page_checksum andbt_page_items(bytea)

On 03/04/2017 02:08 PM, Peter Eisentraut wrote:
> On 3/3/17 09:03, Tomas Vondra wrote:
>> Damn. In my defense, the patch was originally created for an older
>> PostgreSQL version (to investigate issue on a production system), which
>> used that approach to building values. Should have notice it, though.
>>
>> Attached is v2, fixing both issues.
>
> Can we have a test case for page_checksum(), or is that too difficult to
> get running deterministicly?
>

I'm not sure it can be made deterministic. Certainly not on heap pages, 
because then it'd be susceptible to xmin/xmax changes, but we have other 
bits that change even on index pages (say pd_lsn).

So I'm afraid that's not going to fly.
>
> Also, perhaps page_checksum() doesn't need to be superuser-only, but
> I can see arguments for keeping it that way for consistency.
>

Yes, I'll change that.

It won't have much impact in practice, because all functions providing 
the page data (get_raw_page etc.) do require superuser. But you can 
still input the page as a bytea directly, and it's good practice not to 
add unnecessary superuser checks.

regard

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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