Vlad,
I guess I did not understand the full implementation you described
below. Are you proposing a new way of storing multi-segmented keys?
Is this new method still searchable and comparable byte-wise left to
right without knowledge of the key type?
Maybe you can explain this idea a little more thoroughly.
Kevin
Vladislav Vaintroub wrote:
> Anyone wants to comment on that?
> The change would be cheap and fixes at least current multisegment padding
> problem, where 0x00==0x0000==0x000000...
>
>> -----Original Message-----
>> From: Vladislav.Vaintroub@stripped [mailto:Vladislav.Vaintroub@stripped]
>> On Behalf Of Vladislav Vaintroub
>> Sent: Wednesday, February 18, 2009 12:45 AM
>> To: Kevin.Lewis@stripped; 'Lars-Erik Bjørk'
>> Cc: 'Jim Starkey'; 'FalconDev'
>> Subject: RE: Patch for bug#42208
>>
>> Guys, why we're still on alpha stage, maybe we could fix multisegments
>> too?
>>
>> Many (i.e 7 or 8) years ago we used following schema for multisegment
>> keys
>> without padding
>>
>> Suppose we have keys A and B and want to make a multisegment key out of
>> it.
>>
>> The resulting key would be
>> f(A) 0x00 f(B)
>>
>> 0x00 serves as separator and f() is a transformation that converts
>>
>> 0x00=>0x01 0x00
>> 0x01=>0x01 0x01
>>
>> Any other byte remains unchanged.0x00s at the end can be compressed, so
>> we
>> get efficient key is there are only/many NULLs.
>>
>> I do not think the schema is much more complicated than RUN length and
>> padding.
>>
>> Vlad
>>
>> And while we're on it why not to fix integer representation;) Doubles
>> are
>> strange creation by mathematician, exact longlongs would be really
>> nice,
>> not?
>>
>>
>>
>>
>>> -----Original Message-----
>>> From: Kevin.Lewis@stripped [mailto:Kevin.Lewis@stripped]
>>> Sent: Tuesday, February 17, 2009 11:55 PM
>>> To: Lars-Erik Bjørk
>>> Cc: Jim Starkey; Vladislav Vaintroub; 'FalconDev'
>>> Subject: Re: Patch for bug#42208
>>>
>>> According to the blog link forwearded by Mark, Oracle customers don
>> not
>>> like that zero length strings (which ar equal to each other) are
>>> automatically converted to NULLs. Both suggestions take care of that
>>> in
>>> Falcon. So this is the most inportant thing; make a zero length
>> string
>>> equal to 0x00 length 1.
>>>
>>> The question is whether to keep adding 0x00 to other lengths of
>> binary
>>> zero strings. Jim says it does not matter to anyone but QA that 0x00
>>> and 0x0000 sort separately. And Vlad points out that even if we did
>>> this for single field keys, it would not sort them differently for
>>> multisegment key since we always pad them to a RUN length. I think
>>> that
>>> if it does not cause any extra difficulties or comlexity in the code,
>>> why not keep QA happy for single segment keys.
>>>
>>> And I still am unclear why this little change in index order should
>>> cause us to change the ODS format while still in the alpha stage.
>> What
>>> is the downside of a new engine that starts converting zero length
>>> strings into 0x00? New entries will be added to the index after the
>>> NULLS. Older zero length strings would be mixed up with the NULLS
>> and
>>> may not be found for direct searched until the index is rebuilt. We
>>> can
>>> document that as a bug fix in the index, which it is. Nobodies
>> critical
>>> data is depending on us finding all zero length strings.
>>>
>>> Kevin
>>>
>>> Lars-Erik Bjørk wrote:
>>>> Ok, so we probably don't want to do the caching after all then?
>> Does
>>>> anyone else have an opinion on how to proceed on this? Do we agree
>> on
>>>> any best approach?
>>>>
>>>> /Lars-Erik
>>>>
>>>> Jim Starkey wrote:
>>>>> Vladislav Vaintroub wrote:
>>>>>> Hi Lars-Erik,
>>>>>> I wonder if adding 0x00 to the (binary) string values that
>> already
>>> start
>>>>>> with 0x00 would not be less works that modifying index walker
>> etc.
>>> This
>>>>>> looks like huge amount of work you have done (good) but I wonder
>> if
>>>>>> there is
>>>>>> a good reason for it. Assuming (binary) strings that start with
>>> 0x00 are
>>>>>> really seldom, prepending 0x00 to a key after a check is not
>> going
>>> to
>>>>>> be an
>>>>>> expensive operation. And that makes NULL *really* different from
>>>>>> other index
>>>>>> values. And that allows maybe in some distant future index-only
>>>>>> access, so
>>>>>> you can answer "is null/is not null" without extra accessing the
>>>>>> record and
>>>>>> this is a real performance advantage.
>>>>>>
>>>>>>
>>>>> Why do you want to do that? Is the following sufficient:
>>>>>
>>>>> 1. A null is represented as either a zero length key or a
>> missing
>>>>> segment in a multi-segment key. This collates lowest.
>>>>> 2. A zero length binary key is represented by a single byte of
>>> zero.
>>>>> 3. A binary key with a single zero byte is indistinquishable
>> from
>>> a
>>>>> zero length (but non-null) key
>>>>> 4. A binary key with a leading zero byte and a subsequent non-
>> zero
>>>>> byte will collate about #2 and #3.
>>>>>
>>>>> I don't think we really care about the ordering of a non-null,
>> zero
>>>>> length key and and all zero binary key. I don't think anyone else
>>>>> should, either.
>>>>>
>>>>
>>
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>
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