[ZODB-Dev] Some interesting (to some:) numbers

[Adam GROSZER]

Hello Jim,



Tuesday, May 11, 2010, 4:46:46 PM, you wrote:

JF> On Tue, May 11, 2010 at 7:47 AM, Adam GROSZER <agroszer at gmail.com> wrote:
>> Hello Jim,
>>
>> Tuesday, May 11, 2010, 1:37:19 PM, you wrote:
>>
>> JF> On Tue, May 11, 2010 at 7:13 AM, Adam GROSZER <agroszer at gmail.com> wrote:
>>>> Hello Jim,
>>>>
>>>> Tuesday, May 11, 2010, 12:33:04 PM, you wrote:
>>>>
>>>> JF> On Tue, May 11, 2010 at 3:16 AM, Adam GROSZER <agroszer at gmail.com> wrote:
>>>>>> Hello Jim,
>>>>>>
>>>>>> Monday, May 10, 2010, 1:27:00 PM, you wrote:
>>>>>>
>>>>>> JF> On Sun, May 9, 2010 at 4:59 PM, Roel Bruggink <roel at fourdigits.nl> wrote:
>>>>>>>> That's really interesting! Did you notice any issues performance wise, or
>>>>>>>> didn't you check that yet?
>>>>>>
>>>>>> JF> I didn't check performance. I just iterated over a file storage file,
>>>>>> JF> checking compressed and uncompressed pickle sizes.
>>>>>>
>>>>>> I'd say some checksum is then also needed to detect bit failures that
>>>>>> mess up the compressed data.
>>>>
>>>> JF> Why?
>>>>
>>>> I think the gzip algo compresses to a bit-stream, where even one bit
>>>> has an error the rest of the uncompressed data might be a total mess.
>>>> If that one bit is relatively early in the stream it's fatal.
>>>> Salvaging the data is not a joy either.
>>>> I know at this level we should expect that the OS and any underlying
>>>> infrastructure should provide error-free data or fail.
>>>> Tho I've seen some magic situations where the file copied without
>>>> error through a network, but at the end CRC check failed on it :-O
>>
>> JF> How would a checksum help?  All it would do is tell you your hosed.
>> JF> It wouldn't make you any less hosed.
>>
>> Yes, but I would know why it's hosed.

JF> How so?  How would you know why it is hosed.

Because of data corruption in the compressed stream.

JF> Note BTW that the zlib format already includes a checksum.

JF>   http://www.faqs.org/rfcs/rfc1950.html

I missed that. Case closed then ;-) Sorry for the noise.


-- 
Best regards,
 Adam GROSZER                            mailto:agroszer at gmail.com
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